Add some new PolyUtils tests.
Also:
* clean up PolyUtils checks to be correct and consistent.
* fix some bugs discovered by the unit tests.
Bug: skia:
Change-Id: I1a8e07d13cb44fecc67344154dc1002f3f910f5d
Reviewed-on: https://skia-review.googlesource.com/138592
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
diff --git a/src/utils/SkPolyUtils.cpp b/src/utils/SkPolyUtils.cpp
index ea9d649..e323f21 100755
--- a/src/utils/SkPolyUtils.cpp
+++ b/src/utils/SkPolyUtils.cpp
@@ -35,13 +35,20 @@
return 0;
}
-// returns 1 for ccw, -1 for cw and 0 if degenerate
-static int get_winding(const SkPoint* polygonVerts, int polygonSize) {
+// Returns 1 for cw, -1 for ccw and 0 if zero signed area (either degenerate or self-intersecting)
+int SkGetPolygonWinding(const SkPoint* polygonVerts, int polygonSize) {
+ if (polygonSize < 3) {
+ return 0;
+ }
+
// compute area and use sign to determine winding
SkScalar quadArea = 0;
- for (int curr = 0; curr < polygonSize; ++curr) {
+ SkVector v0 = polygonVerts[1] - polygonVerts[0];
+ for (int curr = 1; curr < polygonSize - 1; ++curr) {
int next = (curr + 1) % polygonSize;
- quadArea += polygonVerts[curr].cross(polygonVerts[next]);
+ SkVector v1 = polygonVerts[next] - polygonVerts[0];
+ quadArea += v0.cross(v1);
+ v0 = v1;
}
if (SkScalarNearlyZero(quadArea)) {
return 0;
@@ -111,6 +118,15 @@
return true;
}
+// compute fraction of d along v
+static inline SkScalar compute_param(const SkVector& v, const SkVector& d) {
+ if (SkScalarNearlyZero(v.fX)) {
+ return d.fY / v.fY;
+ } else {
+ return d.fX / v.fX;
+ }
+}
+
// Compute the intersection 'p' between segments s0 and s1, if any.
// 's' is the parametric value for the intersection along 's0' & 't' is the same for 's1'.
// Returns false if there is no intersection.
@@ -132,36 +148,60 @@
SkVector v0 = s0.fP1 - s0.fP0;
SkVector v1 = s1.fP1 - s1.fP0;
- // We should have culled coincident points before this
- SkASSERT(!SkPointPriv::EqualsWithinTolerance(s0.fP0, s0.fP1));
- SkASSERT(!SkPointPriv::EqualsWithinTolerance(s1.fP0, s1.fP1));
-
SkVector d = s1.fP0 - s0.fP0;
SkScalar perpDot = v0.cross(v1);
SkScalar localS, localT;
if (SkScalarNearlyZero(perpDot)) {
// segments are parallel, but not collinear
- if (!SkScalarNearlyZero(d.dot(d), SK_ScalarNearlyZero*SK_ScalarNearlyZero)) {
+ if (!SkScalarNearlyZero(d.cross(v0)) || !SkScalarNearlyZero(d.cross(v1))) {
return false;
}
- // project segment1's endpoints onto segment0
- localS = d.fX / v0.fX;
- localT = 0;
- if (localS < 0 || localS > SK_Scalar1) {
- // the first endpoint doesn't lie on segment0, try the other one
- SkScalar oldLocalS = localS;
- localS = (s1.fP1.fX - s0.fP0.fX) / v0.fX;
- localT = SK_Scalar1;
- if (localS < 0 || localS > SK_Scalar1) {
- // it's possible that segment1's interval surrounds segment0
- // this is false if the params have the same signs, and in that case no collision
- if (localS*oldLocalS > 0) {
+ // Check for degenerate segments
+ if (!SkPointPriv::CanNormalize(v0.fX, v0.fY)) {
+ // Both are degenerate
+ if (!SkPointPriv::CanNormalize(v1.fX, v1.fY)) {
+ // Check if they're the same point
+ if (!SkPointPriv::CanNormalize(d.fX, d.fY)) {
+ *p = s0.fP0;
+ *s = 0;
+ *t = 0;
+ return true;
+ } else {
return false;
}
- // otherwise project segment0's endpoint onto segment1 instead
- localS = 0;
- localT = -d.fX / v1.fX;
+ }
+ // Otherwise project onto segment1
+ localT = compute_param(v1, -d);
+ if (localT < 0 || localT > SK_Scalar1) {
+ return false;
+ }
+ localS = 0;
+ } else {
+ // Project segment1's endpoints onto segment0
+ localS = compute_param(v0, d);
+ localT = 0;
+ if (localS < 0 || localS > SK_Scalar1) {
+ // The first endpoint doesn't lie on segment0
+ // If segment1 is degenerate, then there's no collision
+ if (!SkPointPriv::CanNormalize(v1.fX, v1.fY)) {
+ return false;
+ }
+
+ // Otherwise try the other one
+ SkScalar oldLocalS = localS;
+ localS = compute_param(v0, s1.fP1 - s0.fP0);
+ localT = SK_Scalar1;
+ if (localS < 0 || localS > SK_Scalar1) {
+ // it's possible that segment1's interval surrounds segment0
+ // this is false if params have the same signs, and in that case no collision
+ if (localS*oldLocalS > 0) {
+ return false;
+ }
+ // otherwise project segment0's endpoint onto segment1 instead
+ localS = 0;
+ localT = compute_param(v1, -d);
+ }
}
}
} else {
@@ -175,8 +215,7 @@
}
}
- v0 *= localS;
- *p = s0.fP0 + v0;
+ *p = s0.fP0 + v0*localS;
*s = localS;
*t = localT;
@@ -207,25 +246,49 @@
return localS;
}
-static bool is_convex(const SkTDArray<SkPoint>& poly) {
- if (poly.count() <= 3) {
- return true;
+bool SkIsConvexPolygon(const SkPoint* polygonVerts, int polygonSize) {
+ if (polygonSize < 3) {
+ return false;
}
- SkVector v0 = poly[0] - poly[poly.count() - 1];
- SkVector v1 = poly[1] - poly[poly.count() - 1];
- SkScalar winding = v0.cross(v1);
+ SkScalar lastArea = 0;
+ SkScalar lastPerpDot = 0;
- for (int i = 0; i < poly.count() - 1; ++i) {
- int j = i + 1;
- int k = (i + 2) % poly.count();
-
- SkVector v0 = poly[j] - poly[i];
- SkVector v1 = poly[k] - poly[i];
+ int prevIndex = polygonSize - 1;
+ int currIndex = 0;
+ int nextIndex = 1;
+ SkPoint origin = polygonVerts[0];
+ SkVector v0 = polygonVerts[currIndex] - polygonVerts[prevIndex];
+ SkVector v1 = polygonVerts[nextIndex] - polygonVerts[currIndex];
+ SkVector w0 = polygonVerts[currIndex] - origin;
+ SkVector w1 = polygonVerts[nextIndex] - origin;
+ for (int i = 0; i < polygonSize; ++i) {
+ // Check that winding direction is always the same (otherwise we have a reflex vertex)
SkScalar perpDot = v0.cross(v1);
- if (winding*perpDot < 0) {
+ if (lastPerpDot*perpDot < 0) {
return false;
}
+ if (0 != perpDot) {
+ lastPerpDot = perpDot;
+ }
+
+ // If the signed area ever flips it's concave
+ // TODO: see if we can verify convexity only with signed area
+ SkScalar quadArea = w0.cross(w1);
+ if (quadArea*lastArea < 0) {
+ return false;
+ }
+ if (0 != quadArea) {
+ lastArea = quadArea;
+ }
+
+ prevIndex = currIndex;
+ currIndex = nextIndex;
+ nextIndex = (currIndex + 1) % polygonSize;
+ v0 = v1;
+ v1 = polygonVerts[nextIndex] - polygonVerts[currIndex];
+ w0 = w1;
+ w1 = polygonVerts[nextIndex] - origin;
}
return true;
@@ -281,7 +344,7 @@
}
// get winding direction
- int winding = get_winding(inputPolygonVerts, inputPolygonSize);
+ int winding = SkGetPolygonWinding(inputPolygonVerts, inputPolygonSize);
if (0 == winding) {
return false;
}
@@ -395,7 +458,7 @@
insetPolygon->pop();
}
- return (insetPolygon->count() >= 3 && is_convex(*insetPolygon));
+ return SkIsConvexPolygon(insetPolygon->begin(), insetPolygon->count());
}
///////////////////////////////////////////////////////////////////////////////////////////
@@ -416,6 +479,8 @@
*n = steps;
}
+///////////////////////////////////////////////////////////////////////////////////////////
+
// tolerant less-than comparison
static inline bool nearly_lt(SkScalar a, SkScalar b, SkScalar tolerance = SK_ScalarNearlyZero) {
return a < b - tolerance;
@@ -626,7 +691,7 @@
}
// get winding direction
- int winding = get_winding(inputPolygonVerts, inputPolygonSize);
+ int winding = SkGetPolygonWinding(inputPolygonVerts, inputPolygonSize);
if (0 == winding) {
return false;
}
@@ -787,7 +852,7 @@
}
// check winding of offset polygon (it should be same as the original polygon)
- SkScalar offsetWinding = get_winding(offsetPolygon->begin(), offsetPolygon->count());
+ SkScalar offsetWinding = SkGetPolygonWinding(offsetPolygon->begin(), offsetPolygon->count());
return (winding*offsetWinding > 0 &&
SkIsSimplePolygon(offsetPolygon->begin(), offsetPolygon->count()));
@@ -891,7 +956,7 @@
// get winding direction
// TODO: we do this for all the polygon routines -- might be better to have the client
// compute it and pass it in
- int winding = get_winding(polygonVerts, polygonSize);
+ int winding = SkGetPolygonWinding(polygonVerts, polygonSize);
if (0 == winding) {
return false;
}