Add base types for path ops

Paths contain lines, quads, and cubics, which are
collectively curves.

To work with path intersections, intermediary curves
are constructed. For now, those intermediates use
doubles to guarantee sufficient precision.

The DVector, DPoint, DLine, DQuad, and DCubic
structs encapsulate these intermediate curves.

The DRect and DTriangle structs are created to
describe intersectable areas of interest.

The Bounds struct inherits from SkRect to create
a SkScalar-based rectangle that intersects shared
edges.

This also includes common math equalities and
debugging that the remainder of path ops builds on,
as well as a temporary top-level interface in
include/pathops/SkPathOps.h.
Review URL: https://codereview.chromium.org/12827020

git-svn-id: http://skia.googlecode.com/svn/trunk@8551 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/pathops/SkOpSegment.cpp b/src/pathops/SkOpSegment.cpp
new file mode 100644
index 0000000..627b0af
--- /dev/null
+++ b/src/pathops/SkOpSegment.cpp
@@ -0,0 +1,2795 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "SkIntersections.h"
+#include "SkOpSegment.h"
+#include "SkPathWriter.h"
+#include "TSearch.h"
+
+#define F (false)      // discard the edge
+#define T (true)       // keep the edge
+
+static const bool gUnaryActiveEdge[2][2] = {
+//  from=0  from=1
+//  to=0,1  to=0,1
+    {F, T}, {T, F},
+};
+
+// FIXME: add support for kReverseDifference_Op
+static const bool gActiveEdge[kXOR_PathOp + 1][2][2][2][2] = {
+//                 miFrom=0                              miFrom=1
+//         miTo=0            miTo=1              miTo=0             miTo=1
+//    suFrom=0    1     suFrom=0     1      suFrom=0    1      suFrom=0    1
+//   suTo=0,1 suTo=0,1  suTo=0,1 suTo=0,1  suTo=0,1 suTo=0,1  suTo=0,1 suTo=0,1
+    {{{{F, F}, {F, F}}, {{T, F}, {T, F}}}, {{{T, T}, {F, F}}, {{F, T}, {T, F}}}},  // mi - su
+    {{{{F, F}, {F, F}}, {{F, T}, {F, T}}}, {{{F, F}, {T, T}}, {{F, T}, {T, F}}}},  // mi & su
+    {{{{F, T}, {T, F}}, {{T, T}, {F, F}}}, {{{T, F}, {T, F}}, {{F, F}, {F, F}}}},  // mi | su
+    {{{{F, T}, {T, F}}, {{T, F}, {F, T}}}, {{{T, F}, {F, T}}, {{F, T}, {T, F}}}},  // mi ^ su
+};
+
+#undef F
+#undef T
+
+// OPTIMIZATION: does the following also work, and is it any faster?
+// return outerWinding * innerWinding > 0
+//      || ((outerWinding + innerWinding < 0) ^ ((outerWinding - innerWinding) < 0)))
+bool SkOpSegment::UseInnerWinding(int outerWinding, int innerWinding) {
+    SkASSERT(outerWinding != SK_MaxS32);
+    SkASSERT(innerWinding != SK_MaxS32);
+    int absOut = abs(outerWinding);
+    int absIn = abs(innerWinding);
+    bool result = absOut == absIn ? outerWinding < 0 : absOut < absIn;
+    return result;
+}
+
+bool SkOpSegment::activeAngle(int index, int* done, SkTDArray<SkOpAngle>* angles) {
+    if (activeAngleInner(index, done, angles)) {
+        return true;
+    }
+    int lesser = index;
+    while (--lesser >= 0 && equalPoints(index, lesser)) {
+        if (activeAngleOther(lesser, done, angles)) {
+            return true;
+        }
+    }
+    lesser = index;
+    do {
+        if (activeAngleOther(index, done, angles)) {
+            return true;
+        }
+    } while (++index < fTs.count() && equalPoints(index, lesser));
+    return false;
+}
+
+bool SkOpSegment::activeAngleOther(int index, int* done, SkTDArray<SkOpAngle>* angles) {
+    SkOpSpan* span = &fTs[index];
+    SkOpSegment* other = span->fOther;
+    int oIndex = span->fOtherIndex;
+    return other->activeAngleInner(oIndex, done, angles);
+}
+
+bool SkOpSegment::activeAngleInner(int index, int* done, SkTDArray<SkOpAngle>* angles) {
+    int next = nextExactSpan(index, 1);
+    if (next > 0) {
+        SkOpSpan& upSpan = fTs[index];
+        if (upSpan.fWindValue || upSpan.fOppValue) {
+            addAngle(angles, index, next);
+            if (upSpan.fDone || upSpan.fUnsortableEnd) {
+                (*done)++;
+            } else if (upSpan.fWindSum != SK_MinS32) {
+                return true;
+            }
+        } else if (!upSpan.fDone) {
+            upSpan.fDone = true;
+            fDoneSpans++;
+        }
+    }
+    int prev = nextExactSpan(index, -1);
+    // edge leading into junction
+    if (prev >= 0) {
+        SkOpSpan& downSpan = fTs[prev];
+        if (downSpan.fWindValue || downSpan.fOppValue) {
+            addAngle(angles, index, prev);
+            if (downSpan.fDone) {
+                (*done)++;
+             } else if (downSpan.fWindSum != SK_MinS32) {
+                return true;
+            }
+        } else if (!downSpan.fDone) {
+            downSpan.fDone = true;
+            fDoneSpans++;
+        }
+    }
+    return false;
+}
+
+SkPoint SkOpSegment::activeLeftTop(bool onlySortable, int* firstT) const {
+    SkASSERT(!done());
+    SkPoint topPt = {SK_ScalarMax, SK_ScalarMax};
+    int count = fTs.count();
+    // see if either end is not done since we want smaller Y of the pair
+    bool lastDone = true;
+    bool lastUnsortable = false;
+    double lastT = -1;
+    for (int index = 0; index < count; ++index) {
+        const SkOpSpan& span = fTs[index];
+        if (onlySortable && (span.fUnsortableStart || lastUnsortable)) {
+            goto next;
+        }
+        if (span.fDone && lastDone) {
+            goto next;
+        }
+        if (approximately_negative(span.fT - lastT)) {
+            goto next;
+        }
+        {
+            const SkPoint& xy = xyAtT(&span);
+            if (topPt.fY > xy.fY || (topPt.fY == xy.fY && topPt.fX > xy.fX)) {
+                topPt = xy;
+                if (firstT) {
+                    *firstT = index;
+                }
+            }
+            if (fVerb != SkPath::kLine_Verb && !lastDone) {
+                SkPoint curveTop = (*CurveTop[fVerb])(fPts, lastT, span.fT);
+                if (topPt.fY > curveTop.fY || (topPt.fY == curveTop.fY
+                        && topPt.fX > curveTop.fX)) {
+                    topPt = curveTop;
+                    if (firstT) {
+                        *firstT = index;
+                    }
+                }
+            }
+            lastT = span.fT;
+        }
+next:
+        lastDone = span.fDone;
+        lastUnsortable = span.fUnsortableEnd;
+    }
+    return topPt;
+}
+
+bool SkOpSegment::activeOp(int index, int endIndex, int xorMiMask, int xorSuMask, SkPathOp op) {
+    int sumMiWinding = updateWinding(endIndex, index);
+    int sumSuWinding = updateOppWinding(endIndex, index);
+    if (fOperand) {
+        SkTSwap<int>(sumMiWinding, sumSuWinding);
+    }
+    int maxWinding, sumWinding, oppMaxWinding, oppSumWinding;
+    return activeOp(xorMiMask, xorSuMask, index, endIndex, op, &sumMiWinding, &sumSuWinding,
+            &maxWinding, &sumWinding, &oppMaxWinding, &oppSumWinding);
+}
+
+bool SkOpSegment::activeOp(int xorMiMask, int xorSuMask, int index, int endIndex, SkPathOp op,
+        int* sumMiWinding, int* sumSuWinding,
+        int* maxWinding, int* sumWinding, int* oppMaxWinding, int* oppSumWinding) {
+    setUpWindings(index, endIndex, sumMiWinding, sumSuWinding,
+            maxWinding, sumWinding, oppMaxWinding, oppSumWinding);
+    bool miFrom;
+    bool miTo;
+    bool suFrom;
+    bool suTo;
+    if (operand()) {
+        miFrom = (*oppMaxWinding & xorMiMask) != 0;
+        miTo = (*oppSumWinding & xorMiMask) != 0;
+        suFrom = (*maxWinding & xorSuMask) != 0;
+        suTo = (*sumWinding & xorSuMask) != 0;
+    } else {
+        miFrom = (*maxWinding & xorMiMask) != 0;
+        miTo = (*sumWinding & xorMiMask) != 0;
+        suFrom = (*oppMaxWinding & xorSuMask) != 0;
+        suTo = (*oppSumWinding & xorSuMask) != 0;
+    }
+    bool result = gActiveEdge[op][miFrom][miTo][suFrom][suTo];
+#if DEBUG_ACTIVE_OP
+    SkDebugf("%s op=%s miFrom=%d miTo=%d suFrom=%d suTo=%d result=%d\n", __FUNCTION__,
+            kPathOpStr[op], miFrom, miTo, suFrom, suTo, result);
+#endif
+    return result;
+}
+
+bool SkOpSegment::activeWinding(int index, int endIndex) {
+    int sumWinding = updateWinding(endIndex, index);
+    int maxWinding;
+    return activeWinding(index, endIndex, &maxWinding, &sumWinding);
+}
+
+bool SkOpSegment::activeWinding(int index, int endIndex, int* maxWinding, int* sumWinding) {
+    setUpWinding(index, endIndex, maxWinding, sumWinding);
+    bool from = *maxWinding != 0;
+    bool to = *sumWinding  != 0;
+    bool result = gUnaryActiveEdge[from][to];
+    return result;
+}
+
+void SkOpSegment::addAngle(SkTDArray<SkOpAngle>* anglesPtr, int start, int end) const {
+    SkASSERT(start != end);
+    SkOpAngle* angle = anglesPtr->append();
+#if DEBUG_ANGLE
+    SkTDArray<SkOpAngle>& angles = *anglesPtr;
+    if (angles.count() > 1 && !fTs[start].fTiny) {
+        SkPoint angle0Pt = (*CurvePointAtT[angles[0].verb()])(angles[0].pts(),
+                (*angles[0].spans())[angles[0].start()].fT);
+        SkPoint newPt = (*CurvePointAtT[fVerb])(fPts, fTs[start].fT);
+        SkASSERT(AlmostEqualUlps(angle0Pt.fX, newPt.fX));
+        SkASSERT(AlmostEqualUlps(angle0Pt.fY, newPt.fY));
+    }
+#endif
+    angle->set(fPts, fVerb, this, start, end, fTs);
+}
+
+void SkOpSegment::addCancelOutsides(double tStart, double oStart, SkOpSegment* other, double oEnd) {
+    int tIndex = -1;
+    int tCount = fTs.count();
+    int oIndex = -1;
+    int oCount = other->fTs.count();
+    do {
+        ++tIndex;
+    } while (!approximately_negative(tStart - fTs[tIndex].fT) && tIndex < tCount);
+    int tIndexStart = tIndex;
+    do {
+        ++oIndex;
+    } while (!approximately_negative(oStart - other->fTs[oIndex].fT) && oIndex < oCount);
+    int oIndexStart = oIndex;
+    double nextT;
+    do {
+        nextT = fTs[++tIndex].fT;
+    } while (nextT < 1 && approximately_negative(nextT - tStart));
+    double oNextT;
+    do {
+        oNextT = other->fTs[++oIndex].fT;
+    } while (oNextT < 1 && approximately_negative(oNextT - oStart));
+    // at this point, spans before and after are at:
+    //  fTs[tIndexStart - 1], fTs[tIndexStart], fTs[tIndex]
+    // if tIndexStart == 0, no prior span
+    // if nextT == 1, no following span
+
+    // advance the span with zero winding
+    // if the following span exists (not past the end, non-zero winding)
+    // connect the two edges
+    if (!fTs[tIndexStart].fWindValue) {
+        if (tIndexStart > 0 && fTs[tIndexStart - 1].fWindValue) {
+#if DEBUG_CONCIDENT
+            SkDebugf("%s 1 this=%d other=%d t [%d] %1.9g (%1.9g,%1.9g)\n",
+                    __FUNCTION__, fID, other->fID, tIndexStart - 1,
+                    fTs[tIndexStart].fT, xyAtT(tIndexStart).fX,
+                    xyAtT(tIndexStart).fY);
+#endif
+            addTPair(fTs[tIndexStart].fT, other, other->fTs[oIndex].fT, false,
+                    fTs[tIndexStart].fPt);
+        }
+        if (nextT < 1 && fTs[tIndex].fWindValue) {
+#if DEBUG_CONCIDENT
+            SkDebugf("%s 2 this=%d other=%d t [%d] %1.9g (%1.9g,%1.9g)\n",
+                    __FUNCTION__, fID, other->fID, tIndex,
+                    fTs[tIndex].fT, xyAtT(tIndex).fX,
+                    xyAtT(tIndex).fY);
+#endif
+            addTPair(fTs[tIndex].fT, other, other->fTs[oIndexStart].fT, false, fTs[tIndex].fPt);
+        }
+    } else {
+        SkASSERT(!other->fTs[oIndexStart].fWindValue);
+        if (oIndexStart > 0 && other->fTs[oIndexStart - 1].fWindValue) {
+#if DEBUG_CONCIDENT
+            SkDebugf("%s 3 this=%d other=%d t [%d] %1.9g (%1.9g,%1.9g)\n",
+                    __FUNCTION__, fID, other->fID, oIndexStart - 1,
+                    other->fTs[oIndexStart].fT, other->xyAtT(oIndexStart).fX,
+                    other->xyAtT(oIndexStart).fY);
+            other->debugAddTPair(other->fTs[oIndexStart].fT, *this, fTs[tIndex].fT);
+#endif
+        }
+        if (oNextT < 1 && other->fTs[oIndex].fWindValue) {
+#if DEBUG_CONCIDENT
+            SkDebugf("%s 4 this=%d other=%d t [%d] %1.9g (%1.9g,%1.9g)\n",
+                    __FUNCTION__, fID, other->fID, oIndex,
+                    other->fTs[oIndex].fT, other->xyAtT(oIndex).fX,
+                    other->xyAtT(oIndex).fY);
+            other->debugAddTPair(other->fTs[oIndex].fT, *this, fTs[tIndexStart].fT);
+#endif
+        }
+    }
+}
+
+void SkOpSegment::addCoinOutsides(const SkTDArray<double>& outsideTs, SkOpSegment* other,
+                                  double oEnd) {
+    // walk this to outsideTs[0]
+    // walk other to outsideTs[1]
+    // if either is > 0, add a pointer to the other, copying adjacent winding
+    int tIndex = -1;
+    int oIndex = -1;
+    double tStart = outsideTs[0];
+    double oStart = outsideTs[1];
+    do {
+        ++tIndex;
+    } while (!approximately_negative(tStart - fTs[tIndex].fT));
+    SkPoint ptStart = fTs[tIndex].fPt;
+    do {
+        ++oIndex;
+    } while (!approximately_negative(oStart - other->fTs[oIndex].fT));
+    if (tIndex > 0 || oIndex > 0 || fOperand != other->fOperand) {
+        addTPair(tStart, other, oStart, false, ptStart);
+    }
+    tStart = fTs[tIndex].fT;
+    oStart = other->fTs[oIndex].fT;
+    do {
+        double nextT;
+        do {
+            nextT = fTs[++tIndex].fT;
+        } while (approximately_negative(nextT - tStart));
+        tStart = nextT;
+        ptStart = fTs[tIndex].fPt;
+        do {
+            nextT = other->fTs[++oIndex].fT;
+        } while (approximately_negative(nextT - oStart));
+        oStart = nextT;
+        if (tStart == 1 && oStart == 1 && fOperand == other->fOperand) {
+            break;
+        }
+        addTPair(tStart, other, oStart, false, ptStart);
+    } while (tStart < 1 && oStart < 1 && !approximately_negative(oEnd - oStart));
+}
+
+void SkOpSegment::addCubic(const SkPoint pts[4], bool operand, bool evenOdd) {
+    init(pts, SkPath::kCubic_Verb, operand, evenOdd);
+    fBounds.setCubicBounds(pts);
+}
+
+void SkOpSegment::addCurveTo(int start, int end, SkPathWriter* path, bool active) const {
+    SkPoint edge[4];
+    const SkPoint* ePtr;
+    int lastT = fTs.count() - 1;
+    if (lastT < 0 || (start == 0 && end == lastT) || (start == lastT && end == 0)) {
+        ePtr = fPts;
+    } else {
+    // OPTIMIZE? if not active, skip remainder and return xyAtT(end)
+        subDivide(start, end, edge);
+        ePtr = edge;
+    }
+    if (active) {
+        bool reverse = ePtr == fPts && start != 0;
+        if (reverse) {
+            path->deferredMoveLine(ePtr[fVerb]);
+            switch (fVerb) {
+                case SkPath::kLine_Verb:
+                    path->deferredLine(ePtr[0]);
+                    break;
+                case SkPath::kQuad_Verb:
+                    path->quadTo(ePtr[1], ePtr[0]);
+                    break;
+                case SkPath::kCubic_Verb:
+                    path->cubicTo(ePtr[2], ePtr[1], ePtr[0]);
+                    break;
+                default:
+                    SkASSERT(0);
+            }
+   //         return ePtr[0];
+       } else {
+            path->deferredMoveLine(ePtr[0]);
+            switch (fVerb) {
+                case SkPath::kLine_Verb:
+                    path->deferredLine(ePtr[1]);
+                    break;
+                case SkPath::kQuad_Verb:
+                    path->quadTo(ePtr[1], ePtr[2]);
+                    break;
+                case SkPath::kCubic_Verb:
+                    path->cubicTo(ePtr[1], ePtr[2], ePtr[3]);
+                    break;
+                default:
+                    SkASSERT(0);
+            }
+        }
+    }
+  //  return ePtr[fVerb];
+}
+
+void SkOpSegment::addLine(const SkPoint pts[2], bool operand, bool evenOdd) {
+    init(pts, SkPath::kLine_Verb, operand, evenOdd);
+    fBounds.set(pts, 2);
+}
+
+// add 2 to edge or out of range values to get T extremes
+void SkOpSegment::addOtherT(int index, double otherT, int otherIndex) {
+    SkOpSpan& span = fTs[index];
+#if PIN_ADD_T
+    if (precisely_less_than_zero(otherT)) {
+        otherT = 0;
+    } else if (precisely_greater_than_one(otherT)) {
+        otherT = 1;
+    }
+#endif
+    span.fOtherT = otherT;
+    span.fOtherIndex = otherIndex;
+}
+
+void SkOpSegment::addQuad(const SkPoint pts[3], bool operand, bool evenOdd) {
+    init(pts, SkPath::kQuad_Verb, operand, evenOdd);
+    fBounds.setQuadBounds(pts);
+}
+
+    // Defer all coincident edge processing until
+    // after normal intersections have been computed
+
+// no need to be tricky; insert in normal T order
+// resolve overlapping ts when considering coincidence later
+
+    // add non-coincident intersection. Resulting edges are sorted in T.
+int SkOpSegment::addT(SkOpSegment* other, const SkPoint& pt, double newT) {
+    // FIXME: in the pathological case where there is a ton of intercepts,
+    //  binary search?
+    int insertedAt = -1;
+    size_t tCount = fTs.count();
+    for (size_t index = 0; index < tCount; ++index) {
+        // OPTIMIZATION: if there are three or more identical Ts, then
+        // the fourth and following could be further insertion-sorted so
+        // that all the edges are clockwise or counterclockwise.
+        // This could later limit segment tests to the two adjacent
+        // neighbors, although it doesn't help with determining which
+        // circular direction to go in.
+        if (newT < fTs[index].fT) {
+            insertedAt = index;
+            break;
+        }
+    }
+    SkOpSpan* span;
+    if (insertedAt >= 0) {
+        span = fTs.insert(insertedAt);
+    } else {
+        insertedAt = tCount;
+        span = fTs.append();
+    }
+    span->fT = newT;
+    span->fOther = other;
+    span->fPt = pt;
+    span->fWindSum = SK_MinS32;
+    span->fOppSum = SK_MinS32;
+    span->fWindValue = 1;
+    span->fOppValue = 0;
+    span->fTiny = false;
+    span->fLoop = false;
+    if ((span->fDone = newT == 1)) {
+        ++fDoneSpans;
+    }
+    span->fUnsortableStart = false;
+    span->fUnsortableEnd = false;
+    int less = -1;
+    while (&span[less + 1] - fTs.begin() > 0 && xyAtT(&span[less]) == xyAtT(span)) {
+        if (span[less].fDone) {
+            break;
+        }
+        double tInterval = newT - span[less].fT;
+        if (precisely_negative(tInterval)) {
+            break;
+        }
+        if (fVerb == SkPath::kCubic_Verb) {
+            double tMid = newT - tInterval / 2;
+            SkDPoint midPt = dcubic_xy_at_t(fPts, tMid);
+            if (!midPt.approximatelyEqual(xyAtT(span))) {
+                break;
+            }
+        }
+        span[less].fTiny = true;
+        span[less].fDone = true;
+        if (approximately_negative(newT - span[less].fT)) {
+            if (approximately_greater_than_one(newT)) {
+                SkASSERT(&span[less] - fTs.begin() < fTs.count());
+                span[less].fUnsortableStart = true;
+                if (&span[less - 1] - fTs.begin() >= 0) {
+                    span[less - 1].fUnsortableEnd = true;
+                }
+            }
+            if (approximately_less_than_zero(span[less].fT)) {
+                SkASSERT(&span[less + 1] - fTs.begin() < fTs.count());
+                SkASSERT(&span[less] - fTs.begin() >= 0);
+                span[less + 1].fUnsortableStart = true;
+                span[less].fUnsortableEnd = true;
+            }
+        }
+        ++fDoneSpans;
+        --less;
+    }
+    int more = 1;
+    while (fTs.end() - &span[more - 1] > 1 && xyAtT(&span[more]) == xyAtT(span)) {
+        if (span[more - 1].fDone) {
+            break;
+        }
+        double tEndInterval = span[more].fT - newT;
+        if (precisely_negative(tEndInterval)) {
+            break;
+        }
+        if (fVerb == SkPath::kCubic_Verb) {
+            double tMid = newT - tEndInterval / 2;
+            SkDPoint midEndPt = dcubic_xy_at_t(fPts, tMid);
+            if (!midEndPt.approximatelyEqual(xyAtT(span))) {
+                break;
+            }
+        }
+        span[more - 1].fTiny = true;
+        span[more - 1].fDone = true;
+        if (approximately_negative(span[more].fT - newT)) {
+            if (approximately_greater_than_one(span[more].fT)) {
+                span[more + 1].fUnsortableStart = true;
+                span[more].fUnsortableEnd = true;
+            }
+            if (approximately_less_than_zero(newT)) {
+                span[more].fUnsortableStart = true;
+                span[more - 1].fUnsortableEnd = true;
+            }
+        }
+        ++fDoneSpans;
+        ++more;
+    }
+    return insertedAt;
+}
+
+// set spans from start to end to decrement by one
+// note this walks other backwards
+// FIMXE: there's probably an edge case that can be constructed where
+// two span in one segment are separated by float epsilon on one span but
+// not the other, if one segment is very small. For this
+// case the counts asserted below may or may not be enough to separate the
+// spans. Even if the counts work out, what if the spans aren't correctly
+// sorted? It feels better in such a case to match the span's other span
+// pointer since both coincident segments must contain the same spans.
+void SkOpSegment::addTCancel(double startT, double endT, SkOpSegment* other,
+        double oStartT, double oEndT) {
+    SkASSERT(!approximately_negative(endT - startT));
+    SkASSERT(!approximately_negative(oEndT - oStartT));
+    bool binary = fOperand != other->fOperand;
+    int index = 0;
+    while (!approximately_negative(startT - fTs[index].fT)) {
+        ++index;
+    }
+    int oIndex = other->fTs.count();
+    while (approximately_positive(other->fTs[--oIndex].fT - oEndT))
+        ;
+    double tRatio = (oEndT - oStartT) / (endT - startT);
+    SkOpSpan* test = &fTs[index];
+    SkOpSpan* oTest = &other->fTs[oIndex];
+    SkTDArray<double> outsideTs;
+    SkTDArray<double> oOutsideTs;
+    do {
+        bool decrement = test->fWindValue && oTest->fWindValue && !binary;
+        bool track = test->fWindValue || oTest->fWindValue;
+        double testT = test->fT;
+        double oTestT = oTest->fT;
+        SkOpSpan* span = test;
+        do {
+            if (decrement) {
+                decrementSpan(span);
+            } else if (track && span->fT < 1 && oTestT < 1) {
+                TrackOutside(&outsideTs, span->fT, oTestT);
+            }
+            span = &fTs[++index];
+        } while (approximately_negative(span->fT - testT));
+        SkOpSpan* oSpan = oTest;
+        double otherTMatchStart = oEndT - (span->fT - startT) * tRatio;
+        double otherTMatchEnd = oEndT - (test->fT - startT) * tRatio;
+        SkDEBUGCODE(int originalWindValue = oSpan->fWindValue);
+        while (approximately_negative(otherTMatchStart - oSpan->fT)
+                && !approximately_negative(otherTMatchEnd - oSpan->fT)) {
+    #ifdef SK_DEBUG
+            SkASSERT(originalWindValue == oSpan->fWindValue);
+    #endif
+            if (decrement) {
+                other->decrementSpan(oSpan);
+            } else if (track && oSpan->fT < 1 && testT < 1) {
+                TrackOutside(&oOutsideTs, oSpan->fT, testT);
+            }
+            if (!oIndex) {
+                break;
+            }
+            oSpan = &other->fTs[--oIndex];
+        }
+        test = span;
+        oTest = oSpan;
+    } while (!approximately_negative(endT - test->fT));
+    SkASSERT(!oIndex || approximately_negative(oTest->fT - oStartT));
+    // FIXME: determine if canceled edges need outside ts added
+    if (!done() && outsideTs.count()) {
+        double tStart = outsideTs[0];
+        double oStart = outsideTs[1];
+        addCancelOutsides(tStart, oStart, other, oEndT);
+        int count = outsideTs.count();
+        if (count > 2) {
+            double tStart = outsideTs[count - 2];
+            double oStart = outsideTs[count - 1];
+            addCancelOutsides(tStart, oStart, other, oEndT);
+        }
+    }
+    if (!other->done() && oOutsideTs.count()) {
+        double tStart = oOutsideTs[0];
+        double oStart = oOutsideTs[1];
+        other->addCancelOutsides(tStart, oStart, this, endT);
+    }
+}
+
+int SkOpSegment::addSelfT(SkOpSegment* other, const SkPoint& pt, double newT) {
+    int result = addT(other, pt, newT);
+    SkOpSpan* span = &fTs[result];
+    span->fLoop = true;
+    return result;
+}
+
+int SkOpSegment::addUnsortableT(SkOpSegment* other, bool start, const SkPoint& pt, double newT) {
+    int result = addT(other, pt, newT);
+    SkOpSpan* span = &fTs[result];
+    if (start) {
+        if (result > 0) {
+            span[result - 1].fUnsortableEnd = true;
+        }
+        span[result].fUnsortableStart = true;
+    } else {
+        span[result].fUnsortableEnd = true;
+        if (result + 1 < fTs.count()) {
+            span[result + 1].fUnsortableStart = true;
+        }
+    }
+    return result;
+}
+
+int SkOpSegment::bumpCoincidentThis(const SkOpSpan& oTest, bool opp, int index,
+        SkTDArray<double>* outsideTs) {
+    int oWindValue = oTest.fWindValue;
+    int oOppValue = oTest.fOppValue;
+    if (opp) {
+        SkTSwap<int>(oWindValue, oOppValue);
+    }
+    SkOpSpan* const test = &fTs[index];
+    SkOpSpan* end = test;
+    const double oStartT = oTest.fT;
+    do {
+        if (bumpSpan(end, oWindValue, oOppValue)) {
+            TrackOutside(outsideTs, end->fT, oStartT);
+        }
+        end = &fTs[++index];
+    } while (approximately_negative(end->fT - test->fT));
+    return index;
+}
+
+// because of the order in which coincidences are resolved, this and other
+// may not have the same intermediate points. Compute the corresponding
+// intermediate T values (using this as the master, other as the follower)
+// and walk other conditionally -- hoping that it catches up in the end
+int SkOpSegment::bumpCoincidentOther(const SkOpSpan& test, double oEndT, int& oIndex,
+        SkTDArray<double>* oOutsideTs) {
+    SkOpSpan* const oTest = &fTs[oIndex];
+    SkOpSpan* oEnd = oTest;
+    const double startT = test.fT;
+    const double oStartT = oTest->fT;
+    while (!approximately_negative(oEndT - oEnd->fT)
+            && approximately_negative(oEnd->fT - oStartT)) {
+        zeroSpan(oEnd);
+        TrackOutside(oOutsideTs, oEnd->fT, startT);
+        oEnd = &fTs[++oIndex];
+    }
+    return oIndex;
+}
+
+// FIXME: need to test this case:
+// contourA has two segments that are coincident
+// contourB has two segments that are coincident in the same place
+// each ends up with +2/0 pairs for winding count
+// since logic below doesn't transfer count (only increments/decrements) can this be
+// resolved to +4/0 ?
+
+// set spans from start to end to increment the greater by one and decrement
+// the lesser
+void SkOpSegment::addTCoincident(double startT, double endT, SkOpSegment* other, double oStartT,
+                                 double oEndT) {
+    SkASSERT(!approximately_negative(endT - startT));
+    SkASSERT(!approximately_negative(oEndT - oStartT));
+    bool opp = fOperand ^ other->fOperand;
+    int index = 0;
+    while (!approximately_negative(startT - fTs[index].fT)) {
+        ++index;
+    }
+    int oIndex = 0;
+    while (!approximately_negative(oStartT - other->fTs[oIndex].fT)) {
+        ++oIndex;
+    }
+    SkOpSpan* test = &fTs[index];
+    SkOpSpan* oTest = &other->fTs[oIndex];
+    SkTDArray<double> outsideTs;
+    SkTDArray<double> oOutsideTs;
+    do {
+        // if either span has an opposite value and the operands don't match, resolve first
+ //       SkASSERT(!test->fDone || !oTest->fDone);
+        if (test->fDone || oTest->fDone) {
+            index = advanceCoincidentThis(oTest, opp, index);
+            oIndex = other->advanceCoincidentOther(test, oEndT, oIndex);
+        } else {
+            index = bumpCoincidentThis(*oTest, opp, index, &outsideTs);
+            oIndex = other->bumpCoincidentOther(*test, oEndT, oIndex, &oOutsideTs);
+        }
+        test = &fTs[index];
+        oTest = &other->fTs[oIndex];
+    } while (!approximately_negative(endT - test->fT));
+    SkASSERT(approximately_negative(oTest->fT - oEndT));
+    SkASSERT(approximately_negative(oEndT - oTest->fT));
+    if (!done() && outsideTs.count()) {
+        addCoinOutsides(outsideTs, other, oEndT);
+    }
+    if (!other->done() && oOutsideTs.count()) {
+        other->addCoinOutsides(oOutsideTs, this, endT);
+    }
+}
+
+// FIXME: this doesn't prevent the same span from being added twice
+// fix in caller, SkASSERT here?
+void SkOpSegment::addTPair(double t, SkOpSegment* other, double otherT, bool borrowWind,
+                           const SkPoint& pt) {
+    int tCount = fTs.count();
+    for (int tIndex = 0; tIndex < tCount; ++tIndex) {
+        const SkOpSpan& span = fTs[tIndex];
+        if (!approximately_negative(span.fT - t)) {
+            break;
+        }
+        if (approximately_negative(span.fT - t) && span.fOther == other
+                && approximately_equal(span.fOtherT, otherT)) {
+#if DEBUG_ADD_T_PAIR
+            SkDebugf("%s addTPair duplicate this=%d %1.9g other=%d %1.9g\n",
+                    __FUNCTION__, fID, t, other->fID, otherT);
+#endif
+            return;
+        }
+    }
+#if DEBUG_ADD_T_PAIR
+    SkDebugf("%s addTPair this=%d %1.9g other=%d %1.9g\n",
+            __FUNCTION__, fID, t, other->fID, otherT);
+#endif
+    int insertedAt = addT(other, pt, t);
+    int otherInsertedAt = other->addT(this, pt, otherT);
+    addOtherT(insertedAt, otherT, otherInsertedAt);
+    other->addOtherT(otherInsertedAt, t, insertedAt);
+    matchWindingValue(insertedAt, t, borrowWind);
+    other->matchWindingValue(otherInsertedAt, otherT, borrowWind);
+}
+
+void SkOpSegment::addTwoAngles(int start, int end, SkTDArray<SkOpAngle>* angles) const {
+    // add edge leading into junction
+    int min = SkMin32(end, start);
+    if (fTs[min].fWindValue > 0 || fTs[min].fOppValue > 0) {
+        addAngle(angles, end, start);
+    }
+    // add edge leading away from junction
+    int step = SkSign32(end - start);
+    int tIndex = nextExactSpan(end, step);
+    min = SkMin32(end, tIndex);
+    if (tIndex >= 0 && (fTs[min].fWindValue > 0 || fTs[min].fOppValue > 0)) {
+        addAngle(angles, end, tIndex);
+    }
+}
+
+int SkOpSegment::advanceCoincidentThis(const SkOpSpan* oTest, bool opp, int index) {
+    SkOpSpan* const test = &fTs[index];
+    SkOpSpan* end;
+    do {
+        end = &fTs[++index];
+    } while (approximately_negative(end->fT - test->fT));
+    return index;
+}
+
+int SkOpSegment::advanceCoincidentOther(const SkOpSpan* test, double oEndT, int oIndex) {
+    SkOpSpan* const oTest = &fTs[oIndex];
+    SkOpSpan* oEnd = oTest;
+    const double oStartT = oTest->fT;
+    while (!approximately_negative(oEndT - oEnd->fT)
+            && approximately_negative(oEnd->fT - oStartT)) {
+        oEnd = &fTs[++oIndex];
+    }
+    return oIndex;
+}
+
+bool SkOpSegment::betweenTs(int lesser, double testT, int greater) const {
+    if (lesser > greater) {
+        SkTSwap<int>(lesser, greater);
+    }
+    return approximately_between(fTs[lesser].fT, testT, fTs[greater].fT);
+}
+
+void SkOpSegment::buildAngles(int index, SkTDArray<SkOpAngle>* angles, bool includeOpp) const {
+    double referenceT = fTs[index].fT;
+    int lesser = index;
+    while (--lesser >= 0 && (includeOpp || fTs[lesser].fOther->fOperand == fOperand)
+            && precisely_negative(referenceT - fTs[lesser].fT)) {
+        buildAnglesInner(lesser, angles);
+    }
+    do {
+        buildAnglesInner(index, angles);
+    } while (++index < fTs.count() && (includeOpp || fTs[index].fOther->fOperand == fOperand)
+            && precisely_negative(fTs[index].fT - referenceT));
+}
+
+void SkOpSegment::buildAnglesInner(int index, SkTDArray<SkOpAngle>* angles) const {
+    const SkOpSpan* span = &fTs[index];
+    SkOpSegment* other = span->fOther;
+// if there is only one live crossing, and no coincidence, continue
+// in the same direction
+// if there is coincidence, the only choice may be to reverse direction
+    // find edge on either side of intersection
+    int oIndex = span->fOtherIndex;
+    // if done == -1, prior span has already been processed
+    int step = 1;
+    int next = other->nextExactSpan(oIndex, step);
+   if (next < 0) {
+        step = -step;
+        next = other->nextExactSpan(oIndex, step);
+    }
+    // add candidate into and away from junction
+    other->addTwoAngles(next, oIndex, angles);
+}
+
+int SkOpSegment::computeSum(int startIndex, int endIndex, bool binary) {
+    SkTDArray<SkOpAngle> angles;
+    addTwoAngles(startIndex, endIndex, &angles);
+    buildAngles(endIndex, &angles, false);
+    // OPTIMIZATION: check all angles to see if any have computed wind sum
+    // before sorting (early exit if none)
+    SkTDArray<SkOpAngle*> sorted;
+    bool sortable = SortAngles(angles, &sorted);
+#if DEBUG_SORT
+    sorted[0]->segment()->debugShowSort(__FUNCTION__, sorted, 0, 0, 0);
+#endif
+    if (!sortable) {
+        return SK_MinS32;
+    }
+    int angleCount = angles.count();
+    const SkOpAngle* angle;
+    const SkOpSegment* base;
+    int winding;
+    int oWinding;
+    int firstIndex = 0;
+    do {
+        angle = sorted[firstIndex];
+        base = angle->segment();
+        winding = base->windSum(angle);
+        if (winding != SK_MinS32) {
+            oWinding = base->oppSum(angle);
+            break;
+        }
+        if (++firstIndex == angleCount) {
+            return SK_MinS32;
+        }
+    } while (true);
+    // turn winding into contourWinding
+    int spanWinding = base->spanSign(angle);
+    bool inner = UseInnerWinding(winding + spanWinding, winding);
+#if DEBUG_WINDING
+    SkDebugf("%s spanWinding=%d winding=%d sign=%d inner=%d result=%d\n", __FUNCTION__,
+        spanWinding, winding, angle->sign(), inner,
+        inner ? winding + spanWinding : winding);
+#endif
+    if (inner) {
+        winding += spanWinding;
+    }
+#if DEBUG_SORT
+    base->debugShowSort(__FUNCTION__, sorted, firstIndex, winding, oWinding);
+#endif
+    int nextIndex = firstIndex + 1;
+    int lastIndex = firstIndex != 0 ? firstIndex : angleCount;
+    winding -= base->spanSign(angle);
+    oWinding -= base->oppSign(angle);
+    do {
+        if (nextIndex == angleCount) {
+            nextIndex = 0;
+        }
+        angle = sorted[nextIndex];
+        SkOpSegment* segment = angle->segment();
+        bool opp = base->fOperand ^ segment->fOperand;
+        int maxWinding, oMaxWinding;
+        int spanSign = segment->spanSign(angle);
+        int oppoSign = segment->oppSign(angle);
+        if (opp) {
+            oMaxWinding = oWinding;
+            oWinding -= spanSign;
+            maxWinding = winding;
+            if (oppoSign) {
+                winding -= oppoSign;
+            }
+        } else {
+            maxWinding = winding;
+            winding -= spanSign;
+            oMaxWinding = oWinding;
+            if (oppoSign) {
+                oWinding -= oppoSign;
+            }
+        }
+        if (segment->windSum(angle) == SK_MinS32) {
+            if (opp) {
+                if (UseInnerWinding(oMaxWinding, oWinding)) {
+                    oMaxWinding = oWinding;
+                }
+                if (oppoSign && UseInnerWinding(maxWinding, winding)) {
+                    maxWinding = winding;
+                }
+                (void) segment->markAndChaseWinding(angle, oMaxWinding, maxWinding);
+            } else {
+                if (UseInnerWinding(maxWinding, winding)) {
+                    maxWinding = winding;
+                }
+                if (oppoSign && UseInnerWinding(oMaxWinding, oWinding)) {
+                    oMaxWinding = oWinding;
+                }
+                (void) segment->markAndChaseWinding(angle, maxWinding,
+                        binary ? oMaxWinding : 0);
+            }
+        }
+    } while (++nextIndex != lastIndex);
+    int minIndex = SkMin32(startIndex, endIndex);
+    return windSum(minIndex);
+}
+
+int SkOpSegment::crossedSpanY(const SkPoint& basePt, SkScalar* bestY, double* hitT,
+                              bool* hitSomething, double mid, bool opp, bool current) const {
+    SkScalar bottom = fBounds.fBottom;
+    int bestTIndex = -1;
+    if (bottom <= *bestY) {
+        return bestTIndex;
+    }
+    SkScalar top = fBounds.fTop;
+    if (top >= basePt.fY) {
+        return bestTIndex;
+    }
+    if (fBounds.fLeft > basePt.fX) {
+        return bestTIndex;
+    }
+    if (fBounds.fRight < basePt.fX) {
+        return bestTIndex;
+    }
+    if (fBounds.fLeft == fBounds.fRight) {
+        // if vertical, and directly above test point, wait for another one
+        return AlmostEqualUlps(basePt.fX, fBounds.fLeft) ? SK_MinS32 : bestTIndex;
+    }
+    // intersect ray starting at basePt with edge
+    SkIntersections intersections;
+    // OPTIMIZE: use specialty function that intersects ray with curve,
+    // returning t values only for curve (we don't care about t on ray)
+    int pts = (intersections.*CurveVertical[fVerb])(fPts, top, bottom, basePt.fX, false);
+    if (pts == 0 || (current && pts == 1)) {
+        return bestTIndex;
+    }
+    if (current) {
+        SkASSERT(pts > 1);
+        int closestIdx = 0;
+        double closest = fabs(intersections[0][0] - mid);
+        for (int idx = 1; idx < pts; ++idx) {
+            double test = fabs(intersections[0][idx] - mid);
+            if (closest > test) {
+                closestIdx = idx;
+                closest = test;
+            }
+        }
+        intersections.quickRemoveOne(closestIdx, --pts);
+    }
+    double bestT = -1;
+    for (int index = 0; index < pts; ++index) {
+        double foundT = intersections[0][index];
+        if (approximately_less_than_zero(foundT)
+                    || approximately_greater_than_one(foundT)) {
+            continue;
+        }
+        SkScalar testY = (*CurvePointAtT[fVerb])(fPts, foundT).fY;
+        if (approximately_negative(testY - *bestY)
+                || approximately_negative(basePt.fY - testY)) {
+            continue;
+        }
+        if (pts > 1 && fVerb == SkPath::kLine_Verb) {
+            return SK_MinS32;  // if the intersection is edge on, wait for another one
+        }
+        if (fVerb > SkPath::kLine_Verb) {
+            SkScalar dx = (*CurveSlopeAtT[fVerb])(fPts, foundT).fX;
+            if (approximately_zero(dx)) {
+                return SK_MinS32;  // hit vertical, wait for another one
+            }
+        }
+        *bestY = testY;
+        bestT = foundT;
+    }
+    if (bestT < 0) {
+        return bestTIndex;
+    }
+    SkASSERT(bestT >= 0);
+    SkASSERT(bestT <= 1);
+    int start;
+    int end = 0;
+    do {
+        start = end;
+        end = nextSpan(start, 1);
+    } while (fTs[end].fT < bestT);
+    // FIXME: see next candidate for a better pattern to find the next start/end pair
+    while (start + 1 < end && fTs[start].fDone) {
+        ++start;
+    }
+    if (!isCanceled(start)) {
+        *hitT = bestT;
+        bestTIndex = start;
+        *hitSomething = true;
+    }
+    return bestTIndex;
+}
+
+void SkOpSegment::decrementSpan(SkOpSpan* span) {
+    SkASSERT(span->fWindValue > 0);
+    if (--(span->fWindValue) == 0) {
+        if (!span->fOppValue && !span->fDone) {
+            span->fDone = true;
+            ++fDoneSpans;
+        }
+    }
+}
+
+bool SkOpSegment::bumpSpan(SkOpSpan* span, int windDelta, int oppDelta) {
+    SkASSERT(!span->fDone);
+    span->fWindValue += windDelta;
+    SkASSERT(span->fWindValue >= 0);
+    span->fOppValue += oppDelta;
+    SkASSERT(span->fOppValue >= 0);
+    if (fXor) {
+        span->fWindValue &= 1;
+    }
+    if (fOppXor) {
+        span->fOppValue &= 1;
+    }
+    if (!span->fWindValue && !span->fOppValue) {
+        span->fDone = true;
+        ++fDoneSpans;
+        return true;
+    }
+    return false;
+}
+
+bool SkOpSegment::equalPoints(int greaterTIndex, int lesserTIndex) {
+    SkASSERT(greaterTIndex >= lesserTIndex);
+    double greaterT = fTs[greaterTIndex].fT;
+    double lesserT = fTs[lesserTIndex].fT;
+    if (greaterT == lesserT) {
+        return true;
+    }
+    if (!approximately_negative(greaterT - lesserT)) {
+        return false;
+    }
+    return xyAtT(greaterTIndex) == xyAtT(lesserTIndex);
+}
+
+/*
+ The M and S variable name parts stand for the operators.
+   Mi stands for Minuend (see wiki subtraction, analogous to difference)
+   Su stands for Subtrahend
+ The Opp variable name part designates that the value is for the Opposite operator.
+ Opposite values result from combining coincident spans.
+ */
+SkOpSegment* SkOpSegment::findNextOp(SkTDArray<SkOpSpan*>* chase, int* nextStart, int* nextEnd,
+                                     bool* unsortable, SkPathOp op, const int xorMiMask,
+                                     const int xorSuMask) {
+    const int startIndex = *nextStart;
+    const int endIndex = *nextEnd;
+    SkASSERT(startIndex != endIndex);
+    SkDEBUGCODE(const int count = fTs.count());
+    SkASSERT(startIndex < endIndex ? startIndex < count - 1 : startIndex > 0);
+    const int step = SkSign32(endIndex - startIndex);
+    const int end = nextExactSpan(startIndex, step);
+    SkASSERT(end >= 0);
+    SkOpSpan* endSpan = &fTs[end];
+    SkOpSegment* other;
+    if (isSimple(end)) {
+    // mark the smaller of startIndex, endIndex done, and all adjacent
+    // spans with the same T value (but not 'other' spans)
+#if DEBUG_WINDING
+        SkDebugf("%s simple\n", __FUNCTION__);
+#endif
+        int min = SkMin32(startIndex, endIndex);
+        if (fTs[min].fDone) {
+            return NULL;
+        }
+        markDoneBinary(min);
+        other = endSpan->fOther;
+        *nextStart = endSpan->fOtherIndex;
+        double startT = other->fTs[*nextStart].fT;
+        *nextEnd = *nextStart;
+        do {
+            *nextEnd += step;
+        }
+        while (precisely_zero(startT - other->fTs[*nextEnd].fT));
+        SkASSERT(step < 0 ? *nextEnd >= 0 : *nextEnd < other->fTs.count());
+        return other;
+    }
+    // more than one viable candidate -- measure angles to find best
+    SkTDArray<SkOpAngle> angles;
+    SkASSERT(startIndex - endIndex != 0);
+    SkASSERT((startIndex - endIndex < 0) ^ (step < 0));
+    addTwoAngles(startIndex, end, &angles);
+    buildAngles(end, &angles, true);
+    SkTDArray<SkOpAngle*> sorted;
+    bool sortable = SortAngles(angles, &sorted);
+    int angleCount = angles.count();
+    int firstIndex = findStartingEdge(sorted, startIndex, end);
+    SkASSERT(firstIndex >= 0);
+#if DEBUG_SORT
+    debugShowSort(__FUNCTION__, sorted, firstIndex);
+#endif
+    if (!sortable) {
+        *unsortable = true;
+        return NULL;
+    }
+    SkASSERT(sorted[firstIndex]->segment() == this);
+#if DEBUG_WINDING
+    SkDebugf("%s firstIndex=[%d] sign=%d\n", __FUNCTION__, firstIndex,
+            sorted[firstIndex]->sign());
+#endif
+    int sumMiWinding = updateWinding(endIndex, startIndex);
+    int sumSuWinding = updateOppWinding(endIndex, startIndex);
+    if (operand()) {
+        SkTSwap<int>(sumMiWinding, sumSuWinding);
+    }
+    int nextIndex = firstIndex + 1;
+    int lastIndex = firstIndex != 0 ? firstIndex : angleCount;
+    const SkOpAngle* foundAngle = NULL;
+    bool foundDone = false;
+    // iterate through the angle, and compute everyone's winding
+    SkOpSegment* nextSegment;
+    int activeCount = 0;
+    do {
+        SkASSERT(nextIndex != firstIndex);
+        if (nextIndex == angleCount) {
+            nextIndex = 0;
+        }
+        const SkOpAngle* nextAngle = sorted[nextIndex];
+        nextSegment = nextAngle->segment();
+        int maxWinding, sumWinding, oppMaxWinding, oppSumWinding;
+        bool activeAngle = nextSegment->activeOp(xorMiMask, xorSuMask, nextAngle->start(),
+                nextAngle->end(), op, &sumMiWinding, &sumSuWinding,
+                &maxWinding, &sumWinding, &oppMaxWinding, &oppSumWinding);
+        if (activeAngle) {
+            ++activeCount;
+            if (!foundAngle || (foundDone && activeCount & 1)) {
+                if (nextSegment->tiny(nextAngle)) {
+                    *unsortable = true;
+                    return NULL;
+                }
+                foundAngle = nextAngle;
+                foundDone = nextSegment->done(nextAngle) && !nextSegment->tiny(nextAngle);
+            }
+        }
+        if (nextSegment->done()) {
+            continue;
+        }
+        if (nextSegment->windSum(nextAngle) != SK_MinS32) {
+            continue;
+        }
+        SkOpSpan* last = nextSegment->markAngle(maxWinding, sumWinding, oppMaxWinding,
+                oppSumWinding, activeAngle, nextAngle);
+        if (last) {
+            *chase->append() = last;
+#if DEBUG_WINDING
+            SkDebugf("%s chase.append id=%d\n", __FUNCTION__,
+                    last->fOther->fTs[last->fOtherIndex].fOther->debugID());
+#endif
+        }
+    } while (++nextIndex != lastIndex);
+    markDoneBinary(SkMin32(startIndex, endIndex));
+    if (!foundAngle) {
+        return NULL;
+    }
+    *nextStart = foundAngle->start();
+    *nextEnd = foundAngle->end();
+    nextSegment = foundAngle->segment();
+
+#if DEBUG_WINDING
+    SkDebugf("%s from:[%d] to:[%d] start=%d end=%d\n",
+            __FUNCTION__, debugID(), nextSegment->debugID(), *nextStart, *nextEnd);
+ #endif
+    return nextSegment;
+}
+
+SkOpSegment* SkOpSegment::findNextWinding(SkTDArray<SkOpSpan*>* chase, int* nextStart,
+                                          int* nextEnd, bool* unsortable) {
+    const int startIndex = *nextStart;
+    const int endIndex = *nextEnd;
+    SkASSERT(startIndex != endIndex);
+    SkDEBUGCODE(const int count = fTs.count());
+    SkASSERT(startIndex < endIndex ? startIndex < count - 1 : startIndex > 0);
+    const int step = SkSign32(endIndex - startIndex);
+    const int end = nextExactSpan(startIndex, step);
+    SkASSERT(end >= 0);
+    SkOpSpan* endSpan = &fTs[end];
+    SkOpSegment* other;
+    if (isSimple(end)) {
+    // mark the smaller of startIndex, endIndex done, and all adjacent
+    // spans with the same T value (but not 'other' spans)
+#if DEBUG_WINDING
+        SkDebugf("%s simple\n", __FUNCTION__);
+#endif
+        int min = SkMin32(startIndex, endIndex);
+        if (fTs[min].fDone) {
+            return NULL;
+        }
+        markDoneUnary(min);
+        other = endSpan->fOther;
+        *nextStart = endSpan->fOtherIndex;
+        double startT = other->fTs[*nextStart].fT;
+        *nextEnd = *nextStart;
+        do {
+            *nextEnd += step;
+        }
+        while (precisely_zero(startT - other->fTs[*nextEnd].fT));
+        SkASSERT(step < 0 ? *nextEnd >= 0 : *nextEnd < other->fTs.count());
+        return other;
+    }
+    // more than one viable candidate -- measure angles to find best
+    SkTDArray<SkOpAngle> angles;
+    SkASSERT(startIndex - endIndex != 0);
+    SkASSERT((startIndex - endIndex < 0) ^ (step < 0));
+    addTwoAngles(startIndex, end, &angles);
+    buildAngles(end, &angles, true);
+    SkTDArray<SkOpAngle*> sorted;
+    bool sortable = SortAngles(angles, &sorted);
+    int angleCount = angles.count();
+    int firstIndex = findStartingEdge(sorted, startIndex, end);
+    SkASSERT(firstIndex >= 0);
+#if DEBUG_SORT
+    debugShowSort(__FUNCTION__, sorted, firstIndex);
+#endif
+    if (!sortable) {
+        *unsortable = true;
+        return NULL;
+    }
+    SkASSERT(sorted[firstIndex]->segment() == this);
+#if DEBUG_WINDING
+    SkDebugf("%s firstIndex=[%d] sign=%d\n", __FUNCTION__, firstIndex,
+            sorted[firstIndex]->sign());
+#endif
+    int sumWinding = updateWinding(endIndex, startIndex);
+    int nextIndex = firstIndex + 1;
+    int lastIndex = firstIndex != 0 ? firstIndex : angleCount;
+    const SkOpAngle* foundAngle = NULL;
+    bool foundDone = false;
+    // iterate through the angle, and compute everyone's winding
+    SkOpSegment* nextSegment;
+    int activeCount = 0;
+    do {
+        SkASSERT(nextIndex != firstIndex);
+        if (nextIndex == angleCount) {
+            nextIndex = 0;
+        }
+        const SkOpAngle* nextAngle = sorted[nextIndex];
+        nextSegment = nextAngle->segment();
+        int maxWinding;
+        bool activeAngle = nextSegment->activeWinding(nextAngle->start(), nextAngle->end(),
+                &maxWinding, &sumWinding);
+        if (activeAngle) {
+            ++activeCount;
+            if (!foundAngle || (foundDone && activeCount & 1)) {
+                if (nextSegment->tiny(nextAngle)) {
+                    *unsortable = true;
+                    return NULL;
+                }
+                foundAngle = nextAngle;
+                foundDone = nextSegment->done(nextAngle);
+            }
+        }
+        if (nextSegment->done()) {
+            continue;
+        }
+        if (nextSegment->windSum(nextAngle) != SK_MinS32) {
+            continue;
+        }
+        SkOpSpan* last = nextSegment->markAngle(maxWinding, sumWinding, activeAngle, nextAngle);
+        if (last) {
+            *chase->append() = last;
+#if DEBUG_WINDING
+            SkDebugf("%s chase.append id=%d\n", __FUNCTION__,
+                    last->fOther->fTs[last->fOtherIndex].fOther->debugID());
+#endif
+        }
+    } while (++nextIndex != lastIndex);
+    markDoneUnary(SkMin32(startIndex, endIndex));
+    if (!foundAngle) {
+        return NULL;
+    }
+    *nextStart = foundAngle->start();
+    *nextEnd = foundAngle->end();
+    nextSegment = foundAngle->segment();
+#if DEBUG_WINDING
+    SkDebugf("%s from:[%d] to:[%d] start=%d end=%d\n",
+            __FUNCTION__, debugID(), nextSegment->debugID(), *nextStart, *nextEnd);
+ #endif
+    return nextSegment;
+}
+
+SkOpSegment* SkOpSegment::findNextXor(int* nextStart, int* nextEnd, bool* unsortable) {
+    const int startIndex = *nextStart;
+    const int endIndex = *nextEnd;
+    SkASSERT(startIndex != endIndex);
+    SkDEBUGCODE(int count = fTs.count());
+    SkASSERT(startIndex < endIndex ? startIndex < count - 1
+            : startIndex > 0);
+    int step = SkSign32(endIndex - startIndex);
+    int end = nextExactSpan(startIndex, step);
+    SkASSERT(end >= 0);
+    SkOpSpan* endSpan = &fTs[end];
+    SkOpSegment* other;
+    if (isSimple(end)) {
+#if DEBUG_WINDING
+        SkDebugf("%s simple\n", __FUNCTION__);
+#endif
+        int min = SkMin32(startIndex, endIndex);
+        if (fTs[min].fDone) {
+            return NULL;
+        }
+        markDone(min, 1);
+        other = endSpan->fOther;
+        *nextStart = endSpan->fOtherIndex;
+        double startT = other->fTs[*nextStart].fT;
+        // FIXME: I don't know why the logic here is difference from the winding case
+        SkDEBUGCODE(bool firstLoop = true;)
+        if ((approximately_less_than_zero(startT) && step < 0)
+                || (approximately_greater_than_one(startT) && step > 0)) {
+            step = -step;
+            SkDEBUGCODE(firstLoop = false;)
+        }
+        do {
+            *nextEnd = *nextStart;
+            do {
+                *nextEnd += step;
+            }
+             while (precisely_zero(startT - other->fTs[*nextEnd].fT));
+            if (other->fTs[SkMin32(*nextStart, *nextEnd)].fWindValue) {
+                break;
+            }
+#ifdef SK_DEBUG
+            SkASSERT(firstLoop);
+#endif
+            SkDEBUGCODE(firstLoop = false;)
+            step = -step;
+        } while (true);
+        SkASSERT(step < 0 ? *nextEnd >= 0 : *nextEnd < other->fTs.count());
+        return other;
+    }
+    SkTDArray<SkOpAngle> angles;
+    SkASSERT(startIndex - endIndex != 0);
+    SkASSERT((startIndex - endIndex < 0) ^ (step < 0));
+    addTwoAngles(startIndex, end, &angles);
+    buildAngles(end, &angles, false);
+    SkTDArray<SkOpAngle*> sorted;
+    bool sortable = SortAngles(angles, &sorted);
+    if (!sortable) {
+        *unsortable = true;
+#if DEBUG_SORT
+        debugShowSort(__FUNCTION__, sorted, findStartingEdge(sorted, startIndex, end), 0, 0);
+#endif
+        return NULL;
+    }
+    int angleCount = angles.count();
+    int firstIndex = findStartingEdge(sorted, startIndex, end);
+    SkASSERT(firstIndex >= 0);
+#if DEBUG_SORT
+    debugShowSort(__FUNCTION__, sorted, firstIndex, 0, 0);
+#endif
+    SkASSERT(sorted[firstIndex]->segment() == this);
+    int nextIndex = firstIndex + 1;
+    int lastIndex = firstIndex != 0 ? firstIndex : angleCount;
+    const SkOpAngle* foundAngle = NULL;
+    bool foundDone = false;
+    SkOpSegment* nextSegment;
+    int activeCount = 0;
+    do {
+        SkASSERT(nextIndex != firstIndex);
+        if (nextIndex == angleCount) {
+            nextIndex = 0;
+        }
+        const SkOpAngle* nextAngle = sorted[nextIndex];
+        nextSegment = nextAngle->segment();
+        ++activeCount;
+        if (!foundAngle || (foundDone && activeCount & 1)) {
+            if (nextSegment->tiny(nextAngle)) {
+                *unsortable = true;
+                return NULL;
+            }
+            foundAngle = nextAngle;
+            foundDone = nextSegment->done(nextAngle);
+        }
+        if (nextSegment->done()) {
+            continue;
+        }
+    } while (++nextIndex != lastIndex);
+    markDone(SkMin32(startIndex, endIndex), 1);
+    if (!foundAngle) {
+        return NULL;
+    }
+    *nextStart = foundAngle->start();
+    *nextEnd = foundAngle->end();
+    nextSegment = foundAngle->segment();
+#if DEBUG_WINDING
+    SkDebugf("%s from:[%d] to:[%d] start=%d end=%d\n",
+            __FUNCTION__, debugID(), nextSegment->debugID(), *nextStart, *nextEnd);
+ #endif
+    return nextSegment;
+}
+
+int SkOpSegment::findStartingEdge(const SkTDArray<SkOpAngle*>& sorted, int start, int end) {
+    int angleCount = sorted.count();
+    int firstIndex = -1;
+    for (int angleIndex = 0; angleIndex < angleCount; ++angleIndex) {
+        const SkOpAngle* angle = sorted[angleIndex];
+        if (angle->segment() == this && angle->start() == end &&
+                angle->end() == start) {
+            firstIndex = angleIndex;
+            break;
+        }
+    }
+    return firstIndex;
+}
+
+// FIXME: this is tricky code; needs its own unit test
+// note that fOtherIndex isn't computed yet, so it can't be used here
+void SkOpSegment::findTooCloseToCall() {
+    int count = fTs.count();
+    if (count < 3) {  // require t=0, x, 1 at minimum
+        return;
+    }
+    int matchIndex = 0;
+    int moCount;
+    SkOpSpan* match;
+    SkOpSegment* mOther;
+    do {
+        match = &fTs[matchIndex];
+        mOther = match->fOther;
+        // FIXME: allow quads, cubics to be near coincident?
+        if (mOther->fVerb == SkPath::kLine_Verb) {
+            moCount = mOther->fTs.count();
+            if (moCount >= 3) {
+                break;
+            }
+        }
+        if (++matchIndex >= count) {
+            return;
+        }
+    } while (true);  // require t=0, x, 1 at minimum
+    // OPTIMIZATION: defer matchPt until qualifying toCount is found?
+    const SkPoint* matchPt = &xyAtT(match);
+    // look for a pair of nearby T values that map to the same (x,y) value
+    // if found, see if the pair of other segments share a common point. If
+    // so, the span from here to there is coincident.
+    for (int index = matchIndex + 1; index < count; ++index) {
+        SkOpSpan* test = &fTs[index];
+        if (test->fDone) {
+            continue;
+        }
+        SkOpSegment* tOther = test->fOther;
+        if (tOther->fVerb != SkPath::kLine_Verb) {
+            continue;  // FIXME: allow quads, cubics to be near coincident?
+        }
+        int toCount = tOther->fTs.count();
+        if (toCount < 3) {  // require t=0, x, 1 at minimum
+            continue;
+        }
+        const SkPoint* testPt = &xyAtT(test);
+        if (*matchPt != *testPt) {
+            matchIndex = index;
+            moCount = toCount;
+            match = test;
+            mOther = tOther;
+            matchPt = testPt;
+            continue;
+        }
+        int moStart = -1;
+        int moEnd = -1;
+        double moStartT = 0;
+        double moEndT = 0;
+        for (int moIndex = 0; moIndex < moCount; ++moIndex) {
+            SkOpSpan& moSpan = mOther->fTs[moIndex];
+            if (moSpan.fDone) {
+                continue;
+            }
+            if (moSpan.fOther == this) {
+                if (moSpan.fOtherT == match->fT) {
+                    moStart = moIndex;
+                    moStartT = moSpan.fT;
+                }
+                continue;
+            }
+            if (moSpan.fOther == tOther) {
+                if (tOther->windValueAt(moSpan.fOtherT) == 0) {
+                    moStart = -1;
+                    break;
+                }
+                SkASSERT(moEnd == -1);
+                moEnd = moIndex;
+                moEndT = moSpan.fT;
+            }
+        }
+        if (moStart < 0 || moEnd < 0) {
+            continue;
+        }
+        // FIXME: if moStartT, moEndT are initialized to NaN, can skip this test
+        if (approximately_equal(moStartT, moEndT)) {
+            continue;
+        }
+        int toStart = -1;
+        int toEnd = -1;
+        double toStartT = 0;
+        double toEndT = 0;
+        for (int toIndex = 0; toIndex < toCount; ++toIndex) {
+            SkOpSpan& toSpan = tOther->fTs[toIndex];
+            if (toSpan.fDone) {
+                continue;
+            }
+            if (toSpan.fOther == this) {
+                if (toSpan.fOtherT == test->fT) {
+                    toStart = toIndex;
+                    toStartT = toSpan.fT;
+                }
+                continue;
+            }
+            if (toSpan.fOther == mOther && toSpan.fOtherT == moEndT) {
+                if (mOther->windValueAt(toSpan.fOtherT) == 0) {
+                    moStart = -1;
+                    break;
+                }
+                SkASSERT(toEnd == -1);
+                toEnd = toIndex;
+                toEndT = toSpan.fT;
+            }
+        }
+        // FIXME: if toStartT, toEndT are initialized to NaN, can skip this test
+        if (toStart <= 0 || toEnd <= 0) {
+            continue;
+        }
+        if (approximately_equal(toStartT, toEndT)) {
+            continue;
+        }
+        // test to see if the segment between there and here is linear
+        if (!mOther->isLinear(moStart, moEnd)
+                || !tOther->isLinear(toStart, toEnd)) {
+            continue;
+        }
+        bool flipped = (moStart - moEnd) * (toStart - toEnd) < 1;
+        if (flipped) {
+            mOther->addTCancel(moStartT, moEndT, tOther, toEndT, toStartT);
+        } else {
+            mOther->addTCoincident(moStartT, moEndT, tOther, toStartT, toEndT);
+        }
+    }
+}
+
+// FIXME: either:
+// a) mark spans with either end unsortable as done, or
+// b) rewrite findTop / findTopSegment / findTopContour to iterate further
+//    when encountering an unsortable span
+
+// OPTIMIZATION : for a pair of lines, can we compute points at T (cached)
+// and use more concise logic like the old edge walker code?
+// FIXME: this needs to deal with coincident edges
+SkOpSegment* SkOpSegment::findTop(int* tIndexPtr, int* endIndexPtr, bool* unsortable,
+                                  bool onlySortable) {
+    // iterate through T intersections and return topmost
+    // topmost tangent from y-min to first pt is closer to horizontal
+    SkASSERT(!done());
+    int firstT = -1;
+    /* SkPoint topPt = */ activeLeftTop(onlySortable, &firstT);
+    if (firstT < 0) {
+        *unsortable = true;
+        firstT = 0;
+        while (fTs[firstT].fDone) {
+            SkASSERT(firstT < fTs.count());
+            ++firstT;
+        }
+        *tIndexPtr = firstT;
+        *endIndexPtr = nextExactSpan(firstT, 1);
+        return this;
+    }
+    // sort the edges to find the leftmost
+    int step = 1;
+    int end = nextSpan(firstT, step);
+    if (end == -1) {
+        step = -1;
+        end = nextSpan(firstT, step);
+        SkASSERT(end != -1);
+    }
+    // if the topmost T is not on end, or is three-way or more, find left
+    // look for left-ness from tLeft to firstT (matching y of other)
+    SkTDArray<SkOpAngle> angles;
+    SkASSERT(firstT - end != 0);
+    addTwoAngles(end, firstT, &angles);
+    buildAngles(firstT, &angles, true);
+    SkTDArray<SkOpAngle*> sorted;
+    bool sortable = SortAngles(angles, &sorted);
+    int first = SK_MaxS32;
+    SkScalar top = SK_ScalarMax;
+    int count = sorted.count();
+    for (int index = 0; index < count; ++index) {
+        const SkOpAngle* angle = sorted[index];
+        SkOpSegment* next = angle->segment();
+        SkPathOpsBounds bounds;
+        next->subDivideBounds(angle->end(), angle->start(), &bounds);
+        if (approximately_greater(top, bounds.fTop)) {
+            top = bounds.fTop;
+            first = index;
+        }
+    }
+    SkASSERT(first < SK_MaxS32);
+#if DEBUG_SORT  // || DEBUG_SWAP_TOP
+    sorted[first]->segment()->debugShowSort(__FUNCTION__, sorted, first, 0, 0);
+#endif
+    if (onlySortable && !sortable) {
+        *unsortable = true;
+        return NULL;
+    }
+    // skip edges that have already been processed
+    firstT = first - 1;
+    SkOpSegment* leftSegment;
+    do {
+        if (++firstT == count) {
+            firstT = 0;
+        }
+        const SkOpAngle* angle = sorted[firstT];
+        SkASSERT(!onlySortable || !angle->unsortable());
+        leftSegment = angle->segment();
+        *tIndexPtr = angle->end();
+        *endIndexPtr = angle->start();
+    } while (leftSegment->fTs[SkMin32(*tIndexPtr, *endIndexPtr)].fDone);
+    if (leftSegment->verb() >= SkPath::kQuad_Verb) {
+        const int tIndex = *tIndexPtr;
+        const int endIndex = *endIndexPtr;
+        if (!leftSegment->clockwise(tIndex, endIndex)) {
+            bool swap = !leftSegment->monotonicInY(tIndex, endIndex)
+                    && !leftSegment->serpentine(tIndex, endIndex);
+    #if DEBUG_SWAP_TOP
+            SkDebugf("%s swap=%d serpentine=%d containedByEnds=%d monotonic=%d\n", __FUNCTION__,
+                    swap,
+                    leftSegment->serpentine(tIndex, endIndex),
+                    leftSegment->controlsContainedByEnds(tIndex, endIndex),
+                    leftSegment->monotonicInY(tIndex, endIndex));
+    #endif
+            if (swap) {
+    // FIXME: I doubt it makes sense to (necessarily) swap if the edge was not the first
+    // sorted but merely the first not already processed (i.e., not done)
+                SkTSwap(*tIndexPtr, *endIndexPtr);
+            }
+        }
+    }
+    SkASSERT(!leftSegment->fTs[SkMin32(*tIndexPtr, *endIndexPtr)].fTiny);
+    return leftSegment;
+}
+
+// FIXME: not crazy about this
+// when the intersections are performed, the other index is into an
+// incomplete array. As the array grows, the indices become incorrect
+// while the following fixes the indices up again, it isn't smart about
+// skipping segments whose indices are already correct
+// assuming we leave the code that wrote the index in the first place
+void SkOpSegment::fixOtherTIndex() {
+    int iCount = fTs.count();
+    for (int i = 0; i < iCount; ++i) {
+        SkOpSpan& iSpan = fTs[i];
+        double oT = iSpan.fOtherT;
+        SkOpSegment* other = iSpan.fOther;
+        int oCount = other->fTs.count();
+        for (int o = 0; o < oCount; ++o) {
+            SkOpSpan& oSpan = other->fTs[o];
+            if (oT == oSpan.fT && this == oSpan.fOther && oSpan.fOtherT == iSpan.fT) {
+                iSpan.fOtherIndex = o;
+                break;
+            }
+        }
+    }
+}
+
+void SkOpSegment::init(const SkPoint pts[], SkPath::Verb verb, bool operand, bool evenOdd) {
+    fDoneSpans = 0;
+    fOperand = operand;
+    fXor = evenOdd;
+    fPts = pts;
+    fVerb = verb;
+}
+
+void SkOpSegment::initWinding(int start, int end) {
+    int local = spanSign(start, end);
+    int oppLocal = oppSign(start, end);
+    (void) markAndChaseWinding(start, end, local, oppLocal);
+    // OPTIMIZATION: the reverse mark and chase could skip the first marking
+    (void) markAndChaseWinding(end, start, local, oppLocal);
+}
+
+/*
+when we start with a vertical intersect, we try to use the dx to determine if the edge is to
+the left or the right of vertical. This determines if we need to add the span's
+sign or not. However, this isn't enough.
+If the supplied sign (winding) is zero, then we didn't hit another vertical span, so dx is needed.
+If there was a winding, then it may or may not need adjusting. If the span the winding was borrowed
+from has the same x direction as this span, the winding should change. If the dx is opposite, then
+the same winding is shared by both.
+*/
+void SkOpSegment::initWinding(int start, int end, double tHit, int winding, SkScalar hitDx,
+                              int oppWind, SkScalar hitOppDx) {
+    SkASSERT(hitDx || !winding);
+    SkScalar dx = (*CurveSlopeAtT[fVerb])(fPts, tHit).fX;
+    SkASSERT(dx);
+    int windVal = windValue(SkMin32(start, end));
+#if DEBUG_WINDING_AT_T
+    SkDebugf("%s oldWinding=%d hitDx=%c dx=%c windVal=%d", __FUNCTION__, winding,
+            hitDx ? hitDx > 0 ? '+' : '-' : '0', dx > 0 ? '+' : '-', windVal);
+#endif
+    if (!winding) {
+        winding = dx < 0 ? windVal : -windVal;
+    } else if (winding * dx < 0) {
+        int sideWind = winding + (dx < 0 ? windVal : -windVal);
+        if (abs(winding) < abs(sideWind)) {
+            winding = sideWind;
+        }
+    }
+#if DEBUG_WINDING_AT_T
+    SkDebugf(" winding=%d\n", winding);
+#endif
+    SkDEBUGCODE(int oppLocal = oppSign(start, end));
+    SkASSERT(hitOppDx || !oppWind || !oppLocal);
+    int oppWindVal = oppValue(SkMin32(start, end));
+    if (!oppWind) {
+        oppWind = dx < 0 ? oppWindVal : -oppWindVal;
+    } else if (hitOppDx * dx >= 0) {
+        int oppSideWind = oppWind + (dx < 0 ? oppWindVal : -oppWindVal);
+        if (abs(oppWind) < abs(oppSideWind)) {
+            oppWind = oppSideWind;
+        }
+    }
+    (void) markAndChaseWinding(start, end, winding, oppWind);
+}
+
+bool SkOpSegment::isLinear(int start, int end) const {
+    if (fVerb == SkPath::kLine_Verb) {
+        return true;
+    }
+    if (fVerb == SkPath::kQuad_Verb) {
+        SkDQuad qPart = SkDQuad::SubDivide(fPts, fTs[start].fT, fTs[end].fT);
+        return qPart.isLinear(0, 2);
+    } else {
+        SkASSERT(fVerb == SkPath::kCubic_Verb);
+        SkDCubic cPart = SkDCubic::SubDivide(fPts, fTs[start].fT, fTs[end].fT);
+        return cPart.isLinear(0, 3);
+    }
+}
+
+// OPTIMIZE: successive calls could start were the last leaves off
+// or calls could specialize to walk forwards or backwards
+bool SkOpSegment::isMissing(double startT) const {
+    size_t tCount = fTs.count();
+    for (size_t index = 0; index < tCount; ++index) {
+        if (approximately_zero(startT - fTs[index].fT)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+bool SkOpSegment::isSimple(int end) const {
+    int count = fTs.count();
+    if (count == 2) {
+        return true;
+    }
+    double t = fTs[end].fT;
+    if (approximately_less_than_zero(t)) {
+        return !approximately_less_than_zero(fTs[1].fT);
+    }
+    if (approximately_greater_than_one(t)) {
+        return !approximately_greater_than_one(fTs[count - 2].fT);
+    }
+    return false;
+}
+
+// this span is excluded by the winding rule -- chase the ends
+// as long as they are unambiguous to mark connections as done
+// and give them the same winding value
+SkOpSpan* SkOpSegment::markAndChaseDone(int index, int endIndex, int winding) {
+    int step = SkSign32(endIndex - index);
+    int min = SkMin32(index, endIndex);
+    markDone(min, winding);
+    SkOpSpan* last;
+    SkOpSegment* other = this;
+    while ((other = other->nextChase(&index, step, &min, &last))) {
+        other->markDone(min, winding);
+    }
+    return last;
+}
+
+SkOpSpan* SkOpSegment::markAndChaseDoneBinary(const SkOpAngle* angle, int winding, int oppWinding) {
+    int index = angle->start();
+    int endIndex = angle->end();
+    int step = SkSign32(endIndex - index);
+    int min = SkMin32(index, endIndex);
+    markDoneBinary(min, winding, oppWinding);
+    SkOpSpan* last;
+    SkOpSegment* other = this;
+    while ((other = other->nextChase(&index, step, &min, &last))) {
+        other->markDoneBinary(min, winding, oppWinding);
+    }
+    return last;
+}
+
+SkOpSpan* SkOpSegment::markAndChaseDoneBinary(int index, int endIndex) {
+    int step = SkSign32(endIndex - index);
+    int min = SkMin32(index, endIndex);
+    markDoneBinary(min);
+    SkOpSpan* last;
+    SkOpSegment* other = this;
+    while ((other = other->nextChase(&index, step, &min, &last))) {
+        if (other->done()) {
+            return NULL;
+        }
+        other->markDoneBinary(min);
+    }
+    return last;
+}
+
+SkOpSpan* SkOpSegment::markAndChaseDoneUnary(int index, int endIndex) {
+    int step = SkSign32(endIndex - index);
+    int min = SkMin32(index, endIndex);
+    markDoneUnary(min);
+    SkOpSpan* last;
+    SkOpSegment* other = this;
+    while ((other = other->nextChase(&index, step, &min, &last))) {
+        if (other->done()) {
+            return NULL;
+        }
+        other->markDoneUnary(min);
+    }
+    return last;
+}
+
+SkOpSpan* SkOpSegment::markAndChaseDoneUnary(const SkOpAngle* angle, int winding) {
+    int index = angle->start();
+    int endIndex = angle->end();
+    return markAndChaseDone(index, endIndex, winding);
+}
+
+SkOpSpan* SkOpSegment::markAndChaseWinding(const SkOpAngle* angle, const int winding) {
+    int index = angle->start();
+    int endIndex = angle->end();
+    int step = SkSign32(endIndex - index);
+    int min = SkMin32(index, endIndex);
+    markWinding(min, winding);
+    SkOpSpan* last;
+    SkOpSegment* other = this;
+    while ((other = other->nextChase(&index, step, &min, &last))) {
+        if (other->fTs[min].fWindSum != SK_MinS32) {
+            SkASSERT(other->fTs[min].fWindSum == winding);
+            return NULL;
+        }
+        other->markWinding(min, winding);
+    }
+    return last;
+}
+
+SkOpSpan* SkOpSegment::markAndChaseWinding(int index, int endIndex, int winding, int oppWinding) {
+    int min = SkMin32(index, endIndex);
+    int step = SkSign32(endIndex - index);
+    markWinding(min, winding, oppWinding);
+    SkOpSpan* last;
+    SkOpSegment* other = this;
+    while ((other = other->nextChase(&index, step, &min, &last))) {
+        if (other->fTs[min].fWindSum != SK_MinS32) {
+            SkASSERT(other->fTs[min].fWindSum == winding || other->fTs[min].fLoop);
+            return NULL;
+        }
+        other->markWinding(min, winding, oppWinding);
+    }
+    return last;
+}
+
+SkOpSpan* SkOpSegment::markAndChaseWinding(const SkOpAngle* angle, int winding, int oppWinding) {
+    int start = angle->start();
+    int end = angle->end();
+    return markAndChaseWinding(start, end, winding, oppWinding);
+}
+
+SkOpSpan* SkOpSegment::markAngle(int maxWinding, int sumWinding, bool activeAngle,
+                                const SkOpAngle* angle) {
+    SkASSERT(angle->segment() == this);
+    if (UseInnerWinding(maxWinding, sumWinding)) {
+        maxWinding = sumWinding;
+    }
+    SkOpSpan* last;
+    if (activeAngle) {
+        last = markAndChaseWinding(angle, maxWinding);
+    } else {
+        last = markAndChaseDoneUnary(angle, maxWinding);
+    }
+    return last;
+}
+
+SkOpSpan* SkOpSegment::markAngle(int maxWinding, int sumWinding, int oppMaxWinding,
+                                 int oppSumWinding, bool activeAngle, const SkOpAngle* angle) {
+    SkASSERT(angle->segment() == this);
+    if (UseInnerWinding(maxWinding, sumWinding)) {
+        maxWinding = sumWinding;
+    }
+    if (oppMaxWinding != oppSumWinding && UseInnerWinding(oppMaxWinding, oppSumWinding)) {
+        oppMaxWinding = oppSumWinding;
+    }
+    SkOpSpan* last;
+    if (activeAngle) {
+        last = markAndChaseWinding(angle, maxWinding, oppMaxWinding);
+    } else {
+        last = markAndChaseDoneBinary(angle, maxWinding, oppMaxWinding);
+    }
+    return last;
+}
+
+// FIXME: this should also mark spans with equal (x,y)
+// This may be called when the segment is already marked done. While this
+// wastes time, it shouldn't do any more than spin through the T spans.
+// OPTIMIZATION: abort on first done found (assuming that this code is
+// always called to mark segments done).
+void SkOpSegment::markDone(int index, int winding) {
+  //  SkASSERT(!done());
+    SkASSERT(winding);
+    double referenceT = fTs[index].fT;
+    int lesser = index;
+    while (--lesser >= 0 && precisely_negative(referenceT - fTs[lesser].fT)) {
+        markOneDone(__FUNCTION__, lesser, winding);
+    }
+    do {
+        markOneDone(__FUNCTION__, index, winding);
+    } while (++index < fTs.count() && precisely_negative(fTs[index].fT - referenceT));
+}
+
+void SkOpSegment::markDoneBinary(int index, int winding, int oppWinding) {
+  //  SkASSERT(!done());
+    SkASSERT(winding || oppWinding);
+    double referenceT = fTs[index].fT;
+    int lesser = index;
+    while (--lesser >= 0 && precisely_negative(referenceT - fTs[lesser].fT)) {
+        markOneDoneBinary(__FUNCTION__, lesser, winding, oppWinding);
+    }
+    do {
+        markOneDoneBinary(__FUNCTION__, index, winding, oppWinding);
+    } while (++index < fTs.count() && precisely_negative(fTs[index].fT - referenceT));
+}
+
+void SkOpSegment::markDoneBinary(int index) {
+    double referenceT = fTs[index].fT;
+    int lesser = index;
+    while (--lesser >= 0 && precisely_negative(referenceT - fTs[lesser].fT)) {
+        markOneDoneBinary(__FUNCTION__, lesser);
+    }
+    do {
+        markOneDoneBinary(__FUNCTION__, index);
+    } while (++index < fTs.count() && precisely_negative(fTs[index].fT - referenceT));
+}
+
+void SkOpSegment::markDoneUnary(int index) {
+    double referenceT = fTs[index].fT;
+    int lesser = index;
+    while (--lesser >= 0 && precisely_negative(referenceT - fTs[lesser].fT)) {
+        markOneDoneUnary(__FUNCTION__, lesser);
+    }
+    do {
+        markOneDoneUnary(__FUNCTION__, index);
+    } while (++index < fTs.count() && precisely_negative(fTs[index].fT - referenceT));
+}
+
+void SkOpSegment::markOneDone(const char* funName, int tIndex, int winding) {
+    SkOpSpan* span = markOneWinding(funName, tIndex, winding);
+    if (!span) {
+        return;
+    }
+    span->fDone = true;
+    fDoneSpans++;
+}
+
+void SkOpSegment::markOneDoneBinary(const char* funName, int tIndex) {
+    SkOpSpan* span = verifyOneWinding(funName, tIndex);
+    if (!span) {
+        return;
+    }
+    span->fDone = true;
+    fDoneSpans++;
+}
+
+void SkOpSegment::markOneDoneBinary(const char* funName, int tIndex, int winding, int oppWinding) {
+    SkOpSpan* span = markOneWinding(funName, tIndex, winding, oppWinding);
+    if (!span) {
+        return;
+    }
+    span->fDone = true;
+    fDoneSpans++;
+}
+
+void SkOpSegment::markOneDoneUnary(const char* funName, int tIndex) {
+    SkOpSpan* span = verifyOneWindingU(funName, tIndex);
+    if (!span) {
+        return;
+    }
+    span->fDone = true;
+    fDoneSpans++;
+}
+
+SkOpSpan* SkOpSegment::markOneWinding(const char* funName, int tIndex, int winding) {
+    SkOpSpan& span = fTs[tIndex];
+    if (span.fDone) {
+        return NULL;
+    }
+#if DEBUG_MARK_DONE
+    debugShowNewWinding(funName, span, winding);
+#endif
+    SkASSERT(span.fWindSum == SK_MinS32 || span.fWindSum == winding);
+#ifdef SK_DEBUG
+    SkASSERT(abs(winding) <= gDebugMaxWindSum);
+#endif
+    span.fWindSum = winding;
+    return &span;
+}
+
+SkOpSpan* SkOpSegment::markOneWinding(const char* funName, int tIndex, int winding,
+                                      int oppWinding) {
+    SkOpSpan& span = fTs[tIndex];
+    if (span.fDone) {
+        return NULL;
+    }
+#if DEBUG_MARK_DONE
+    debugShowNewWinding(funName, span, winding, oppWinding);
+#endif
+    SkASSERT(span.fWindSum == SK_MinS32 || span.fWindSum == winding);
+#ifdef SK_DEBUG
+    SkASSERT(abs(winding) <= gDebugMaxWindSum);
+#endif
+    span.fWindSum = winding;
+    SkASSERT(span.fOppSum == SK_MinS32 || span.fOppSum == oppWinding);
+#ifdef SK_DEBUG
+    SkASSERT(abs(oppWinding) <= gDebugMaxWindSum);
+#endif
+    span.fOppSum = oppWinding;
+    return &span;
+}
+
+// from http://stackoverflow.com/questions/1165647/how-to-determine-if-a-list-of-polygon-points-are-in-clockwise-order
+bool SkOpSegment::clockwise(int tStart, int tEnd) const {
+    SkASSERT(fVerb != SkPath::kLine_Verb);
+    SkPoint edge[4];
+    subDivide(tStart, tEnd, edge);
+    double sum = (edge[0].fX - edge[fVerb].fX) * (edge[0].fY + edge[fVerb].fY);
+    if (fVerb == SkPath::kCubic_Verb) {
+        SkScalar lesser = SkTMin<SkScalar>(edge[0].fY, edge[3].fY);
+        if (edge[1].fY < lesser && edge[2].fY < lesser) {
+            SkDLine tangent1 = {{ {edge[0].fX, edge[0].fY}, {edge[1].fX, edge[1].fY} }};
+            SkDLine tangent2 = {{ {edge[2].fX, edge[2].fY}, {edge[3].fX, edge[3].fY} }};
+            if (SkIntersections::Test(tangent1, tangent2)) {
+                SkPoint topPt = cubic_top(fPts, fTs[tStart].fT, fTs[tEnd].fT);
+                sum += (topPt.fX - edge[0].fX) * (topPt.fY + edge[0].fY);
+                sum += (edge[3].fX - topPt.fX) * (edge[3].fY + topPt.fY);
+                return sum <= 0;
+            }
+        }
+    }
+    for (int idx = 0; idx < fVerb; ++idx){
+        sum += (edge[idx + 1].fX - edge[idx].fX) * (edge[idx + 1].fY + edge[idx].fY);
+    }
+    return sum <= 0;
+}
+
+bool SkOpSegment::monotonicInY(int tStart, int tEnd) const {
+    if (fVerb == SkPath::kLine_Verb) {
+        return false;
+    }
+    if (fVerb == SkPath::kQuad_Verb) {
+        SkDQuad dst = SkDQuad::SubDivide(fPts, fTs[tStart].fT, fTs[tEnd].fT);
+        return dst.monotonicInY();
+    }
+    SkASSERT(fVerb == SkPath::kCubic_Verb);
+    SkDCubic dst = SkDCubic::SubDivide(fPts, fTs[tStart].fT, fTs[tEnd].fT);
+    return dst.monotonicInY();
+}
+
+bool SkOpSegment::serpentine(int tStart, int tEnd) const {
+    if (fVerb != SkPath::kCubic_Verb) {
+        return false;
+    }
+    SkDCubic dst = SkDCubic::SubDivide(fPts, fTs[tStart].fT, fTs[tEnd].fT);
+    return dst.serpentine();
+}
+
+SkOpSpan* SkOpSegment::verifyOneWinding(const char* funName, int tIndex) {
+    SkOpSpan& span = fTs[tIndex];
+    if (span.fDone) {
+        return NULL;
+    }
+#if DEBUG_MARK_DONE
+    debugShowNewWinding(funName, span, span.fWindSum, span.fOppSum);
+#endif
+    SkASSERT(span.fWindSum != SK_MinS32);
+    SkASSERT(span.fOppSum != SK_MinS32);
+    return &span;
+}
+
+SkOpSpan* SkOpSegment::verifyOneWindingU(const char* funName, int tIndex) {
+    SkOpSpan& span = fTs[tIndex];
+    if (span.fDone) {
+        return NULL;
+    }
+#if DEBUG_MARK_DONE
+    debugShowNewWinding(funName, span, span.fWindSum);
+#endif
+    SkASSERT(span.fWindSum != SK_MinS32);
+    return &span;
+}
+
+// note that just because a span has one end that is unsortable, that's
+// not enough to mark it done. The other end may be sortable, allowing the
+// span to be added.
+// FIXME: if abs(start - end) > 1, mark intermediates as unsortable on both ends
+void SkOpSegment::markUnsortable(int start, int end) {
+    SkOpSpan* span = &fTs[start];
+    if (start < end) {
+#if DEBUG_UNSORTABLE
+        debugShowNewWinding(__FUNCTION__, *span, 0);
+#endif
+        span->fUnsortableStart = true;
+    } else {
+        --span;
+#if DEBUG_UNSORTABLE
+        debugShowNewWinding(__FUNCTION__, *span, 0);
+#endif
+        span->fUnsortableEnd = true;
+    }
+    if (!span->fUnsortableStart || !span->fUnsortableEnd || span->fDone) {
+        return;
+    }
+    span->fDone = true;
+    fDoneSpans++;
+}
+
+void SkOpSegment::markWinding(int index, int winding) {
+//    SkASSERT(!done());
+    SkASSERT(winding);
+    double referenceT = fTs[index].fT;
+    int lesser = index;
+    while (--lesser >= 0 && precisely_negative(referenceT - fTs[lesser].fT)) {
+        markOneWinding(__FUNCTION__, lesser, winding);
+    }
+    do {
+        markOneWinding(__FUNCTION__, index, winding);
+   } while (++index < fTs.count() && precisely_negative(fTs[index].fT - referenceT));
+}
+
+void SkOpSegment::markWinding(int index, int winding, int oppWinding) {
+//    SkASSERT(!done());
+    SkASSERT(winding || oppWinding);
+    double referenceT = fTs[index].fT;
+    int lesser = index;
+    while (--lesser >= 0 && precisely_negative(referenceT - fTs[lesser].fT)) {
+        markOneWinding(__FUNCTION__, lesser, winding, oppWinding);
+    }
+    do {
+        markOneWinding(__FUNCTION__, index, winding, oppWinding);
+   } while (++index < fTs.count() && precisely_negative(fTs[index].fT - referenceT));
+}
+
+void SkOpSegment::matchWindingValue(int tIndex, double t, bool borrowWind) {
+    int nextDoorWind = SK_MaxS32;
+    int nextOppWind = SK_MaxS32;
+    if (tIndex > 0) {
+        const SkOpSpan& below = fTs[tIndex - 1];
+        if (approximately_negative(t - below.fT)) {
+            nextDoorWind = below.fWindValue;
+            nextOppWind = below.fOppValue;
+        }
+    }
+    if (nextDoorWind == SK_MaxS32 && tIndex + 1 < fTs.count()) {
+        const SkOpSpan& above = fTs[tIndex + 1];
+        if (approximately_negative(above.fT - t)) {
+            nextDoorWind = above.fWindValue;
+            nextOppWind = above.fOppValue;
+        }
+    }
+    if (nextDoorWind == SK_MaxS32 && borrowWind && tIndex > 0 && t < 1) {
+        const SkOpSpan& below = fTs[tIndex - 1];
+        nextDoorWind = below.fWindValue;
+        nextOppWind = below.fOppValue;
+    }
+    if (nextDoorWind != SK_MaxS32) {
+        SkOpSpan& newSpan = fTs[tIndex];
+        newSpan.fWindValue = nextDoorWind;
+        newSpan.fOppValue = nextOppWind;
+        if (!nextDoorWind && !nextOppWind && !newSpan.fDone) {
+            newSpan.fDone = true;
+            ++fDoneSpans;
+        }
+    }
+}
+
+// return span if when chasing, two or more radiating spans are not done
+// OPTIMIZATION: ? multiple spans is detected when there is only one valid
+// candidate and the remaining spans have windValue == 0 (canceled by
+// coincidence). The coincident edges could either be removed altogether,
+// or this code could be more complicated in detecting this case. Worth it?
+bool SkOpSegment::multipleSpans(int end) const {
+    return end > 0 && end < fTs.count() - 1;
+}
+
+bool SkOpSegment::nextCandidate(int* start, int* end) const {
+    while (fTs[*end].fDone) {
+        if (fTs[*end].fT == 1) {
+            return false;
+        }
+        ++(*end);
+    }
+    *start = *end;
+    *end = nextExactSpan(*start, 1);
+    return true;
+}
+
+SkOpSegment* SkOpSegment::nextChase(int* index, const int step, int* min, SkOpSpan** last) {
+    int end = nextExactSpan(*index, step);
+    SkASSERT(end >= 0);
+    if (multipleSpans(end)) {
+        *last = &fTs[end];
+        return NULL;
+    }
+    const SkOpSpan& endSpan = fTs[end];
+    SkOpSegment* other = endSpan.fOther;
+    *index = endSpan.fOtherIndex;
+    SkASSERT(index >= 0);
+    int otherEnd = other->nextExactSpan(*index, step);
+    SkASSERT(otherEnd >= 0);
+    *min = SkMin32(*index, otherEnd);
+    return other;
+}
+
+// This has callers for two different situations: one establishes the end
+// of the current span, and one establishes the beginning of the next span
+// (thus the name). When this is looking for the end of the current span,
+// coincidence is found when the beginning Ts contain -step and the end
+// contains step. When it is looking for the beginning of the next, the
+// first Ts found can be ignored and the last Ts should contain -step.
+// OPTIMIZATION: probably should split into two functions
+int SkOpSegment::nextSpan(int from, int step) const {
+    const SkOpSpan& fromSpan = fTs[from];
+    int count = fTs.count();
+    int to = from;
+    while (step > 0 ? ++to < count : --to >= 0) {
+        const SkOpSpan& span = fTs[to];
+        if (approximately_zero(span.fT - fromSpan.fT)) {
+            continue;
+        }
+        return to;
+    }
+    return -1;
+}
+
+// FIXME
+// this returns at any difference in T, vs. a preset minimum. It may be
+// that all callers to nextSpan should use this instead.
+// OPTIMIZATION splitting this into separate loops for up/down steps
+// would allow using precisely_negative instead of precisely_zero
+int SkOpSegment::nextExactSpan(int from, int step) const {
+    const SkOpSpan& fromSpan = fTs[from];
+    int count = fTs.count();
+    int to = from;
+    while (step > 0 ? ++to < count : --to >= 0) {
+        const SkOpSpan& span = fTs[to];
+        if (precisely_zero(span.fT - fromSpan.fT)) {
+            continue;
+        }
+        return to;
+    }
+    return -1;
+}
+
+void SkOpSegment::setUpWindings(int index, int endIndex, int* sumMiWinding, int* sumSuWinding,
+        int* maxWinding, int* sumWinding, int* oppMaxWinding, int* oppSumWinding) {
+    int deltaSum = spanSign(index, endIndex);
+    int oppDeltaSum = oppSign(index, endIndex);
+    if (operand()) {
+        *maxWinding = *sumSuWinding;
+        *sumWinding = *sumSuWinding -= deltaSum;
+        *oppMaxWinding = *sumMiWinding;
+        *oppSumWinding = *sumMiWinding -= oppDeltaSum;
+    } else {
+        *maxWinding = *sumMiWinding;
+        *sumWinding = *sumMiWinding -= deltaSum;
+        *oppMaxWinding = *sumSuWinding;
+        *oppSumWinding = *sumSuWinding -= oppDeltaSum;
+    }
+}
+
+// This marks all spans unsortable so that this info is available for early
+// exclusion in find top and others. This could be optimized to only mark
+// adjacent spans that unsortable. However, this makes it difficult to later
+// determine starting points for edge detection in find top and the like.
+bool SkOpSegment::SortAngles(const SkTDArray<SkOpAngle>& angles,
+                             SkTDArray<SkOpAngle*>* angleList) {
+    bool sortable = true;
+    int angleCount = angles.count();
+    int angleIndex;
+    angleList->setReserve(angleCount);
+    for (angleIndex = 0; angleIndex < angleCount; ++angleIndex) {
+        const SkOpAngle& angle = angles[angleIndex];
+        *angleList->append() = const_cast<SkOpAngle*>(&angle);
+        sortable &= !angle.unsortable();
+    }
+    if (sortable) {
+        QSort<SkOpAngle>(angleList->begin(), angleList->end() - 1);
+        for (angleIndex = 0; angleIndex < angleCount; ++angleIndex) {
+            if (angles[angleIndex].unsortable()) {
+                sortable = false;
+                break;
+            }
+        }
+    }
+    if (!sortable) {
+        for (angleIndex = 0; angleIndex < angleCount; ++angleIndex) {
+            const SkOpAngle& angle = angles[angleIndex];
+            angle.segment()->markUnsortable(angle.start(), angle.end());
+        }
+    }
+    return sortable;
+}
+
+void SkOpSegment::subDivide(int start, int end, SkPoint edge[4]) const {
+    edge[0] = fTs[start].fPt;
+    edge[fVerb] = fTs[end].fPt;
+    if (fVerb == SkPath::kQuad_Verb || fVerb == SkPath::kCubic_Verb) {
+        SkDPoint sub[2] = {{ edge[0].fX, edge[0].fY}, {edge[fVerb].fX, edge[fVerb].fY }};
+        if (fVerb == SkPath::kQuad_Verb) {
+            edge[1] = SkDQuad::SubDivide(fPts, sub[0], sub[1], fTs[start].fT,
+                    fTs[end].fT).asSkPoint();
+        } else {
+            SkDCubic::SubDivide(fPts, sub[0], sub[1], fTs[start].fT, fTs[end].fT, sub);
+            edge[1] = sub[0].asSkPoint();
+            edge[2] = sub[1].asSkPoint();
+        }
+    }
+}
+
+void SkOpSegment::subDivideBounds(int start, int end, SkPathOpsBounds* bounds) const {
+    SkPoint edge[4];
+    subDivide(start, end, edge);
+    (bounds->*SetCurveBounds[fVerb])(edge);
+}
+
+bool SkOpSegment::tiny(const SkOpAngle* angle) const {
+    int start = angle->start();
+    int end = angle->end();
+    const SkOpSpan& mSpan = fTs[SkMin32(start, end)];
+    return mSpan.fTiny;
+}
+
+void SkOpSegment::TrackOutside(SkTDArray<double>* outsideTs, double end, double start) {
+    int outCount = outsideTs->count();
+    if (outCount == 0 || !approximately_negative(end - (*outsideTs)[outCount - 2])) {
+        *outsideTs->append() = end;
+        *outsideTs->append() = start;
+    }
+}
+
+void SkOpSegment::undoneSpan(int* start, int* end) {
+    size_t tCount = fTs.count();
+    size_t index;
+    for (index = 0; index < tCount; ++index) {
+        if (!fTs[index].fDone) {
+            break;
+        }
+    }
+    SkASSERT(index < tCount - 1);
+    *start = index;
+    double startT = fTs[index].fT;
+    while (approximately_negative(fTs[++index].fT - startT))
+        SkASSERT(index < tCount);
+    SkASSERT(index < tCount);
+    *end = index;
+}
+
+int SkOpSegment::updateOppWinding(int index, int endIndex) const {
+    int lesser = SkMin32(index, endIndex);
+    int oppWinding = oppSum(lesser);
+    int oppSpanWinding = oppSign(index, endIndex);
+    if (oppSpanWinding && UseInnerWinding(oppWinding - oppSpanWinding, oppWinding)
+            && oppWinding != SK_MaxS32) {
+        oppWinding -= oppSpanWinding;
+    }
+    return oppWinding;
+}
+
+int SkOpSegment::updateOppWinding(const SkOpAngle* angle) const {
+    int startIndex = angle->start();
+    int endIndex = angle->end();
+    return updateOppWinding(endIndex, startIndex);
+}
+
+int SkOpSegment::updateOppWindingReverse(const SkOpAngle* angle) const {
+    int startIndex = angle->start();
+    int endIndex = angle->end();
+    return updateOppWinding(startIndex, endIndex);
+}
+
+int SkOpSegment::updateWinding(int index, int endIndex) const {
+    int lesser = SkMin32(index, endIndex);
+    int winding = windSum(lesser);
+    int spanWinding = spanSign(index, endIndex);
+    if (winding && UseInnerWinding(winding - spanWinding, winding) && winding != SK_MaxS32) {
+        winding -= spanWinding;
+    }
+    return winding;
+}
+
+int SkOpSegment::updateWinding(const SkOpAngle* angle) const {
+    int startIndex = angle->start();
+    int endIndex = angle->end();
+    return updateWinding(endIndex, startIndex);
+}
+
+int SkOpSegment::updateWindingReverse(const SkOpAngle* angle) const {
+    int startIndex = angle->start();
+    int endIndex = angle->end();
+    return updateWinding(startIndex, endIndex);
+}
+
+int SkOpSegment::windingAtT(double tHit, int tIndex, bool crossOpp, SkScalar* dx) const {
+    if (approximately_zero(tHit - t(tIndex))) {  // if we hit the end of a span, disregard
+        return SK_MinS32;
+    }
+    int winding = crossOpp ? oppSum(tIndex) : windSum(tIndex);
+    SkASSERT(winding != SK_MinS32);
+    int windVal = crossOpp ? oppValue(tIndex) : windValue(tIndex);
+#if DEBUG_WINDING_AT_T
+    SkDebugf("%s oldWinding=%d windValue=%d", __FUNCTION__, winding, windVal);
+#endif
+    // see if a + change in T results in a +/- change in X (compute x'(T))
+    *dx = (*CurveSlopeAtT[fVerb])(fPts, tHit).fX;
+    if (fVerb > SkPath::kLine_Verb && approximately_zero(*dx)) {
+        *dx = fPts[2].fX - fPts[1].fX - *dx;
+    }
+    if (*dx == 0) {
+#if DEBUG_WINDING_AT_T
+        SkDebugf(" dx=0 winding=SK_MinS32\n");
+#endif
+        return SK_MinS32;
+    }
+    if (winding * *dx > 0) {  // if same signs, result is negative
+        winding += *dx > 0 ? -windVal : windVal;
+    }
+#if DEBUG_WINDING_AT_T
+    SkDebugf(" dx=%c winding=%d\n", *dx > 0 ? '+' : '-', winding);
+#endif
+    return winding;
+}
+
+int SkOpSegment::windSum(const SkOpAngle* angle) const {
+    int start = angle->start();
+    int end = angle->end();
+    int index = SkMin32(start, end);
+    return windSum(index);
+}
+
+int SkOpSegment::windValue(const SkOpAngle* angle) const {
+    int start = angle->start();
+    int end = angle->end();
+    int index = SkMin32(start, end);
+    return windValue(index);
+}
+
+int SkOpSegment::windValueAt(double t) const {
+    int count = fTs.count();
+    for (int index = 0; index < count; ++index) {
+        if (fTs[index].fT == t) {
+            return fTs[index].fWindValue;
+        }
+    }
+    SkASSERT(0);
+    return 0;
+}
+
+void SkOpSegment::zeroSpan(SkOpSpan* span) {
+    SkASSERT(span->fWindValue > 0 || span->fOppValue > 0);
+    span->fWindValue = 0;
+    span->fOppValue = 0;
+    SkASSERT(!span->fDone);
+    span->fDone = true;
+    ++fDoneSpans;
+}
+    
+#if DEBUG_SWAP_TOP
+bool SkOpSegment::controlsContainedByEnds(int tStart, int tEnd) const {
+    if (fVerb != SkPath::kCubic_Verb) {
+        return false;
+    }
+    SkDCubic dst = SkDCubic::SubDivide(fPts, fTs[tStart].fT, fTs[tEnd].fT);
+    return dst.controlsContainedByEnds();
+}
+#endif
+
+#if DEBUG_CONCIDENT
+// SkASSERT if pair has not already been added
+void SkOpSegment::debugAddTPair(double t, const SkOpSegment& other, double otherT) const {
+    for (int i = 0; i < fTs.count(); ++i) {
+        if (fTs[i].fT == t && fTs[i].fOther == &other && fTs[i].fOtherT == otherT) {
+            return;
+        }
+    }
+    SkASSERT(0);
+}
+#endif
+
+#if DEBUG_CONCIDENT
+void SkOpSegment::debugShowTs() const {
+    SkDebugf("%s id=%d", __FUNCTION__, fID);
+    int lastWind = -1;
+    int lastOpp = -1;
+    double lastT = -1;
+    int i;
+    for (i = 0; i < fTs.count(); ++i) {
+        bool change = lastT != fTs[i].fT || lastWind != fTs[i].fWindValue
+                || lastOpp != fTs[i].fOppValue;
+        if (change && lastWind >= 0) {
+            SkDebugf(" t=%1.3g %1.9g,%1.9g w=%d o=%d]",
+                    lastT, xyAtT(i - 1).fX, xyAtT(i - 1).fY, lastWind, lastOpp);
+        }
+        if (change) {
+            SkDebugf(" [o=%d", fTs[i].fOther->fID);
+            lastWind = fTs[i].fWindValue;
+            lastOpp = fTs[i].fOppValue;
+            lastT = fTs[i].fT;
+        } else {
+            SkDebugf(",%d", fTs[i].fOther->fID);
+        }
+    }
+    if (i <= 0) {
+        return;
+    }
+    SkDebugf(" t=%1.3g %1.9g,%1.9g w=%d o=%d]",
+            lastT, xyAtT(i - 1).fX, xyAtT(i - 1).fY, lastWind, lastOpp);
+    if (fOperand) {
+        SkDebugf(" operand");
+    }
+    if (done()) {
+        SkDebugf(" done");
+    }
+    SkDebugf("\n");
+}
+#endif
+
+#if DEBUG_ACTIVE_SPANS
+void SkOpSegment::debugShowActiveSpans() const {
+    if (done()) {
+        return;
+    }
+#if DEBUG_ACTIVE_SPANS_SHORT_FORM
+    int lastId = -1;
+    double lastT = -1;
+#endif
+    for (int i = 0; i < fTs.count(); ++i) {
+        SkASSERT(&fTs[i] == &fTs[i].fOther->fTs[fTs[i].fOtherIndex].fOther->
+                fTs[fTs[i].fOther->fTs[fTs[i].fOtherIndex].fOtherIndex]);
+        if (fTs[i].fDone) {
+            continue;
+        }
+#if DEBUG_ACTIVE_SPANS_SHORT_FORM
+        if (lastId == fID && lastT == fTs[i].fT) {
+            continue;
+        }
+        lastId = fID;
+        lastT = fTs[i].fT;
+#endif
+        SkDebugf("%s id=%d", __FUNCTION__, fID);
+        SkDebugf(" (%1.9g,%1.9g", fPts[0].fX, fPts[0].fY);
+        for (int vIndex = 1; vIndex <= fVerb; ++vIndex) {
+            SkDebugf(" %1.9g,%1.9g", fPts[vIndex].fX, fPts[vIndex].fY);
+        }
+        const SkOpSpan* span = &fTs[i];
+        SkDebugf(") t=%1.9g (%1.9g,%1.9g)", span->fT, xAtT(span), yAtT(span));
+        int iEnd = i + 1;
+        while (fTs[iEnd].fT < 1 && approximately_equal(fTs[i].fT, fTs[iEnd].fT)) {
+            ++iEnd;
+        }
+        SkDebugf(" tEnd=%1.9g", fTs[iEnd].fT);
+        const SkOpSegment* other = fTs[i].fOther;
+        SkDebugf(" other=%d otherT=%1.9g otherIndex=%d windSum=",
+                other->fID, fTs[i].fOtherT, fTs[i].fOtherIndex);
+        if (fTs[i].fWindSum == SK_MinS32) {
+            SkDebugf("?");
+        } else {
+            SkDebugf("%d", fTs[i].fWindSum);
+        }
+        SkDebugf(" windValue=%d oppValue=%d\n", fTs[i].fWindValue, fTs[i].fOppValue);
+    }
+}
+#endif
+
+
+#if DEBUG_MARK_DONE || DEBUG_UNSORTABLE
+void SkOpSegment::debugShowNewWinding(const char* fun, const SkOpSpan& span, int winding) {
+    const SkPoint& pt = xyAtT(&span);
+    SkDebugf("%s id=%d", fun, fID);
+    SkDebugf(" (%1.9g,%1.9g", fPts[0].fX, fPts[0].fY);
+    for (int vIndex = 1; vIndex <= fVerb; ++vIndex) {
+        SkDebugf(" %1.9g,%1.9g", fPts[vIndex].fX, fPts[vIndex].fY);
+    }
+    SkASSERT(&span == &span.fOther->fTs[span.fOtherIndex].fOther->
+            fTs[span.fOther->fTs[span.fOtherIndex].fOtherIndex]);
+    SkDebugf(") t=%1.9g [%d] (%1.9g,%1.9g) tEnd=%1.9g newWindSum=%d windSum=",
+            span.fT, span.fOther->fTs[span.fOtherIndex].fOtherIndex, pt.fX, pt.fY,
+            (&span)[1].fT, winding);
+    if (span.fWindSum == SK_MinS32) {
+        SkDebugf("?");
+    } else {
+        SkDebugf("%d", span.fWindSum);
+    }
+    SkDebugf(" windValue=%d\n", span.fWindValue);
+}
+
+void SkOpSegment::debugShowNewWinding(const char* fun, const SkOpSpan& span, int winding,
+                                      int oppWinding) {
+    const SkPoint& pt = xyAtT(&span);
+    SkDebugf("%s id=%d", fun, fID);
+    SkDebugf(" (%1.9g,%1.9g", fPts[0].fX, fPts[0].fY);
+    for (int vIndex = 1; vIndex <= fVerb; ++vIndex) {
+        SkDebugf(" %1.9g,%1.9g", fPts[vIndex].fX, fPts[vIndex].fY);
+    }
+    SkASSERT(&span == &span.fOther->fTs[span.fOtherIndex].fOther->
+            fTs[span.fOther->fTs[span.fOtherIndex].fOtherIndex]);
+    SkDebugf(") t=%1.9g [%d] (%1.9g,%1.9g) tEnd=%1.9g newWindSum=%d newOppSum=%d oppSum=",
+            span.fT, span.fOther->fTs[span.fOtherIndex].fOtherIndex, pt.fX, pt.fY,
+            (&span)[1].fT, winding, oppWinding);
+    if (span.fOppSum == SK_MinS32) {
+        SkDebugf("?");
+    } else {
+        SkDebugf("%d", span.fOppSum);
+    }
+    SkDebugf(" windSum=");
+    if (span.fWindSum == SK_MinS32) {
+        SkDebugf("?");
+    } else {
+        SkDebugf("%d", span.fWindSum);
+    }
+    SkDebugf(" windValue=%d\n", span.fWindValue);
+}
+#endif
+
+#if DEBUG_SORT || DEBUG_SWAP_TOP
+void SkOpSegment::debugShowSort(const char* fun, const SkTDArray<SkOpAngle*>& angles, int first,
+        const int contourWinding, const int oppContourWinding) const {
+    if (--gDebugSortCount < 0) {
+        return;
+    }
+    SkASSERT(angles[first]->segment() == this);
+    SkASSERT(angles.count() > 1);
+    int lastSum = contourWinding;
+    int oppLastSum = oppContourWinding;
+    const SkOpAngle* firstAngle = angles[first];
+    int windSum = lastSum - spanSign(firstAngle);
+    int oppoSign = oppSign(firstAngle);
+    int oppWindSum = oppLastSum - oppoSign;
+    #define WIND_AS_STRING(x) char x##Str[12]; if (!valid_wind(x)) strcpy(x##Str, "?"); \
+        else snprintf(x##Str, sizeof(x##Str), "%d", x)
+    WIND_AS_STRING(contourWinding);
+    WIND_AS_STRING(oppContourWinding);
+    SkDebugf("%s %s contourWinding=%s oppContourWinding=%s sign=%d\n", fun, __FUNCTION__,
+            contourWindingStr, oppContourWindingStr, spanSign(angles[first]));
+    int index = first;
+    bool firstTime = true;
+    do {
+        const SkOpAngle& angle = *angles[index];
+        const SkOpSegment& segment = *angle.segment();
+        int start = angle.start();
+        int end = angle.end();
+        const SkOpSpan& sSpan = segment.fTs[start];
+        const SkOpSpan& eSpan = segment.fTs[end];
+        const SkOpSpan& mSpan = segment.fTs[SkMin32(start, end)];
+        bool opp = segment.fOperand ^ fOperand;
+        if (!firstTime) {
+            oppoSign = segment.oppSign(&angle);
+            if (opp) {
+                oppLastSum = oppWindSum;
+                oppWindSum -= segment.spanSign(&angle);
+                if (oppoSign) {
+                    lastSum = windSum;
+                    windSum -= oppoSign;
+                }
+            } else {
+                lastSum = windSum;
+                windSum -= segment.spanSign(&angle);
+                if (oppoSign) {
+                    oppLastSum = oppWindSum;
+                    oppWindSum -= oppoSign;
+                }
+            }
+        }
+        SkDebugf("%s [%d] %s", __FUNCTION__, index,
+                angle.unsortable() ? "*** UNSORTABLE *** " : "");
+    #if COMPACT_DEBUG_SORT
+        SkDebugf("id=%d %s start=%d (%1.9g,%,1.9g) end=%d (%1.9g,%,1.9g)",
+                segment.fID, kLVerbStr[segment.fVerb],
+                start, segment.xAtT(&sSpan), segment.yAtT(&sSpan), end,
+                segment.xAtT(&eSpan), segment.yAtT(&eSpan));
+    #else
+        switch (segment.fVerb) {
+            case SkPath::kLine_Verb:
+                SkDebugf(LINE_DEBUG_STR, LINE_DEBUG_DATA(segment.fPts));
+                break;
+            case SkPath::kQuad_Verb:
+                SkDebugf(QUAD_DEBUG_STR, QUAD_DEBUG_DATA(segment.fPts));
+                break;
+            case SkPath::kCubic_Verb:
+                SkDebugf(CUBIC_DEBUG_STR, CUBIC_DEBUG_DATA(segment.fPts));
+                break;
+            default:
+                SkASSERT(0);
+        }
+        SkDebugf(" tStart=%1.9g tEnd=%1.9g", sSpan.fT, eSpan.fT);
+    #endif
+        SkDebugf(" sign=%d windValue=%d windSum=", angle.sign(), mSpan.fWindValue);
+        #ifdef SK_DEBUG
+            winding_printf(mSpan.fWindSum);
+        #endif
+        int last, wind;
+        if (opp) {
+            last = oppLastSum;
+            wind = oppWindSum;
+        } else {
+            last = lastSum;
+            wind = windSum;
+        }
+        bool useInner = valid_wind(last) && valid_wind(wind) && UseInnerWinding(last, wind);
+        WIND_AS_STRING(last);
+        WIND_AS_STRING(wind);
+        WIND_AS_STRING(lastSum);
+        WIND_AS_STRING(oppLastSum);
+        WIND_AS_STRING(windSum);
+        WIND_AS_STRING(oppWindSum);
+        #undef WIND_AS_STRING
+        if (!oppoSign) {
+            SkDebugf(" %s->%s (max=%s)", lastStr, windStr, useInner ? windStr : lastStr);
+        } else {
+            SkDebugf(" %s->%s (%s->%s)", lastStr, windStr, opp ? lastSumStr : oppLastSumStr,
+                    opp ? windSumStr : oppWindSumStr);
+        }
+        SkDebugf(" done=%d tiny=%d opp=%d\n", mSpan.fDone, mSpan.fTiny, opp);
+#if false && DEBUG_ANGLE
+        angle.debugShow(segment.xyAtT(&sSpan));
+#endif
+        ++index;
+        if (index == angles.count()) {
+            index = 0;
+        }
+        if (firstTime) {
+            firstTime = false;
+        }
+    } while (index != first);
+}
+
+void SkOpSegment::debugShowSort(const char* fun, const SkTDArray<SkOpAngle*>& angles, int first) {
+    const SkOpAngle* firstAngle = angles[first];
+    const SkOpSegment* segment = firstAngle->segment();
+    int winding = segment->updateWinding(firstAngle);
+    int oppWinding = segment->updateOppWinding(firstAngle);
+    debugShowSort(fun, angles, first, winding, oppWinding);
+}
+
+#endif
+
+#if DEBUG_SHOW_WINDING
+int SkOpSegment::debugShowWindingValues(int slotCount, int ofInterest) const {
+    if (!(1 << fID & ofInterest)) {
+        return 0;
+    }
+    int sum = 0;
+    SkTDArray<char> slots;
+    slots.setCount(slotCount * 2);
+    memset(slots.begin(), ' ', slotCount * 2);
+    for (int i = 0; i < fTs.count(); ++i) {
+   //     if (!(1 << fTs[i].fOther->fID & ofInterest)) {
+   //         continue;
+   //     }
+        sum += fTs[i].fWindValue;
+        slots[fTs[i].fOther->fID - 1] = as_digit(fTs[i].fWindValue);
+        sum += fTs[i].fOppValue;
+        slots[slotCount + fTs[i].fOther->fID - 1] = as_digit(fTs[i].fOppValue);
+    }
+    SkDebugf("%s id=%2d %.*s | %.*s\n", __FUNCTION__, fID, slotCount, slots.begin(), slotCount,
+            slots.begin() + slotCount);
+    return sum;
+}
+#endif