Fix handling of radii scaling to force the result to always be less
than a given side.
BUG=472147
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1567723004

Review URL: https://codereview.chromium.org/1567723004
diff --git a/src/core/SkRRect.cpp b/src/core/SkRRect.cpp
index ad62e5b..c8b3a6b 100644
--- a/src/core/SkRRect.cpp
+++ b/src/core/SkRRect.cpp
@@ -5,6 +5,7 @@
  * found in the LICENSE file.
  */
 
+#include <cmath>
 #include "SkRRect.h"
 #include "SkMatrix.h"
 
@@ -109,28 +110,6 @@
     SkDEBUGCODE(this->validate();)
 }
 
-/*
- *  TODO: clean this guy up and possibly add to SkScalar.h
- */
-static inline SkScalar SkScalarDecULP(SkScalar value) {
-#if SK_SCALAR_IS_FLOAT
-        return SkBits2Float(SkFloat2Bits(value) - 1);
-#else
-    #error "need impl for doubles"
-#endif
-}
-
- /**
- *  We need all combinations of predicates to be true to have a "safe" radius value.
- */
-static SkScalar clamp_radius_check_predicates(SkScalar rad, SkScalar min, SkScalar max) {
-    SkASSERT(min < max);
-    if (rad > max - min || min + rad > max || max - rad < min) {
-        rad = SkScalarDecULP(rad);
-    }
-    return rad;
-}
-
 // These parameters intentionally double. Apropos crbug.com/463920, if one of the
 // radii is huge while the other is small, single precision math can completely
 // miss the fact that a scale is required.
@@ -141,6 +120,48 @@
     return curMin;
 }
 
+// This code assumes that a and b fit in in a float, and therefore the resulting smaller value of
+// a and b will fit in a float. The side of the rectangle may be larger than a float.
+// Scale must be less than or equal to the ratio limit / (*a + *b).
+static void adjust_radii(double limit, double scale, float* a, float* b) {
+    SkASSERT(scale < 1.0 && scale > 0.0);
+    // This check is conservative. (double)*a + (double)*b >= (double)(*a + *b)
+    if ((double)*a + (double)*b > limit) {
+        float* minRadius = a;
+        float* maxRadius = b;
+        // Force minRadius to be the smaller of the two.
+        if (*minRadius > *maxRadius) {
+            SkTSwap(minRadius, maxRadius);
+        }
+        // newMinRadius must be float in order to give the actual value of the radius.
+        // The newMinRadius will always be smaller than limit. The largest that minRadius can be
+        // is 1/2 the ratio of minRadius : (minRadius + maxRadius), therefore in the resulting
+        // division, minRadius can be no larger than 1/2 limit + ULP.
+        float newMinRadius = *minRadius * scale;
+        *minRadius = newMinRadius;
+        // Because newMaxRadius is the result of a double to float conversion, it can be larger
+        // than limit, but only by one ULP.
+        float newMaxRadius = (float)(limit - newMinRadius);
+        // If newMaxRadius is larger than the same value as a double, then it needs to be
+        // reduced by one ULP to be less than limit - newMinRadius.
+        // Note: nexttowardf is a c99 call and should be std::nexttoward, but this is not
+        // implemented in the ARM compiler.
+        if (newMaxRadius > limit - newMinRadius) {
+            newMaxRadius = nexttowardf(newMaxRadius, limit - newMinRadius);
+        }
+        // This handles the case where both sets of radii are larger than a side by differing
+        // scale factors. The one that needs the larger scale factor (the radii with less
+        // overlap) will produce radii that are short enough just using the smaller scale factor
+        // from the side where the radii overlap is larger.
+        *maxRadius = SkMinScalar(scale * *maxRadius, newMaxRadius);
+    } else {
+        *a *= scale;
+        *b *= scale;
+    }
+    SkASSERT(*a >= 0.0f && *b >= 0.0f);
+    SkASSERT((*a + *b) <= limit);
+}
+
 void SkRRect::setRectRadii(const SkRect& rect, const SkVector radii[4]) {
     fRect = rect;
     fRect.sort();
@@ -190,29 +211,21 @@
     // If f < 1, then all corner radii are reduced by multiplying them by f."
     double scale = 1.0;
 
-    scale = compute_min_scale(fRadii[0].fX, fRadii[1].fX, fRect.width(),  scale);
-    scale = compute_min_scale(fRadii[1].fY, fRadii[2].fY, fRect.height(), scale);
-    scale = compute_min_scale(fRadii[2].fX, fRadii[3].fX, fRect.width(),  scale);
-    scale = compute_min_scale(fRadii[3].fY, fRadii[0].fY, fRect.height(), scale);
+    // The sides of the rectangle may be larger than a float.
+    double width = (double)fRect.fRight - (double)fRect.fLeft;
+    double height = (double)fRect.fBottom - (double)fRect.fTop;
+    scale = compute_min_scale(fRadii[0].fX, fRadii[1].fX, width,  scale);
+    scale = compute_min_scale(fRadii[1].fY, fRadii[2].fY, height, scale);
+    scale = compute_min_scale(fRadii[2].fX, fRadii[3].fX, width,  scale);
+    scale = compute_min_scale(fRadii[3].fY, fRadii[0].fY, height, scale);
 
     if (scale < 1.0) {
-        for (int i = 0; i < 4; ++i) {
-            fRadii[i].fX *= scale;
-            fRadii[i].fY *= scale;
-        }
+        adjust_radii(width,  scale, &fRadii[0].fX, &fRadii[1].fX);
+        adjust_radii(height, scale, &fRadii[1].fY, &fRadii[2].fY);
+        adjust_radii(width,  scale, &fRadii[2].fX, &fRadii[3].fX);
+        adjust_radii(height, scale, &fRadii[3].fY, &fRadii[0].fY);
     }
 
-    // https://bug.skia.org/3239 -- its possible that we can hit the following inconsistency:
-    //     rad == bounds.bottom - bounds.top
-    //     bounds.bottom - radius < bounds.top
-    //     YIKES
-    // We need to detect and "fix" this now, otherwise we can have the following wackiness:
-    //     path.addRRect(rrect);
-    //     rrect.rect() != path.getBounds()
-    for (int i = 0; i < 4; ++i) {
-        fRadii[i].fX = clamp_radius_check_predicates(fRadii[i].fX, fRect.fLeft, fRect.fRight);
-        fRadii[i].fY = clamp_radius_check_predicates(fRadii[i].fY, fRect.fTop, fRect.fBottom);
-    }
     // At this point we're either oval, simple, or complex (not empty or rect).
     this->computeType();
 
diff --git a/tests/DrawPathTest.cpp b/tests/DrawPathTest.cpp
index 364a297..e9aa449 100644
--- a/tests/DrawPathTest.cpp
+++ b/tests/DrawPathTest.cpp
@@ -313,6 +313,39 @@
     REPORTER_ASSERT(reporter, filteredPath.isEmpty());
 }
 
+// http://crbug.com/472147
+// This is a simplified version from the bug. RRect radii not properly scaled.
+static void test_crbug_472147_simple(skiatest::Reporter* reporter) {
+    SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(1000, 1000));
+    SkCanvas* canvas = surface->getCanvas();
+    SkPaint p;
+    SkRect r = SkRect::MakeLTRB(-246.0f, 33.0f, 848.0f, 33554464.0f);
+    SkVector radii[4] = {
+        { 13.0f, 8.0f }, { 170.0f, 2.0 }, { 256.0f, 33554430.0f }, { 120.0f, 5.0f }
+    };
+    SkRRect rr;
+    rr.setRectRadii(r, radii);
+    canvas->drawRRect(rr, p);
+}
+
+// http://crbug.com/472147
+// RRect radii not properly scaled.
+static void test_crbug_472147_actual(skiatest::Reporter* reporter) {
+    SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(1000, 1000));
+    SkCanvas* canvas = surface->getCanvas();
+    SkPaint p;
+    SkRect r = SkRect::MakeLTRB(-246.0f, 33.0f, 848.0f, 33554464.0f);
+    SkVector radii[4] = {
+        { 13.0f, 8.0f }, { 170.0f, 2.0 }, { 256.0f, 33554430.0f }, { 120.0f, 5.0f }
+    };
+    SkRRect rr;
+    rr.setRectRadii(r, radii);
+    canvas->clipRRect(rr, SkRegion::kIntersect_Op, false);
+
+    SkRect r2 = SkRect::MakeLTRB(0, 33, 1102, 33554464);
+    canvas->drawRect(r2, p);
+}
+
 DEF_TEST(DrawPath, reporter) {
     test_giantaa();
     test_bug533();
@@ -325,6 +358,8 @@
     if (false) test_crbug131181();
     test_infinite_dash(reporter);
     test_crbug_165432(reporter);
+    test_crbug_472147_simple(reporter);
+    test_crbug_472147_actual(reporter);
     test_big_aa_rect(reporter);
     test_halfway();
 }