re-chop if we fail on a big-bad-cubic

BUG=629455
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2159223005

Review-Url: https://codereview.chromium.org/2159223005

2 files changed, 34 insertions, 2 deletions

diff --git a/src/core/SkEdgeClipper.cpp b/src/core/SkEdgeClipper.cpp
index 85c519d364..b5ac27ae59 100644
--- a/src/core/SkEdgeClipper.cpp
+++ b/src/core/SkEdgeClipper.cpp
@@ -263,9 +263,25 @@ static void chop_cubic_in_Y(SkPoint pts[4], const SkRect& clip) {
     if (pts[0].fY < clip.fTop) {
         SkPoint tmp[7];
         chop_mono_cubic_at_y(pts, clip.fTop, tmp);
+
+        /*
+         *  For a large range in the points, we can do a poor job of chopping, such that the t
+         *  we computed resulted in the lower cubic still being partly above the clip.
+         *
+         *  If just the first or first 2 Y values are above the fTop, we can just smash them
+         *  down. If the first 3 Ys are above fTop, we can't smash all 3, as that can really
+         *  distort the cubic. In this case, we take the first output (tmp[3..6] and treat it as
+         *  a guess, and re-chop against fTop. Then we fall through to checking if we need to
+         *  smash the first 1 or 2 Y values.
+         */
+        if (tmp[3].fY < clip.fTop && tmp[4].fY < clip.fTop && tmp[5].fY < clip.fTop) {
+            SkPoint tmp2[4];
+            memcpy(tmp2, &tmp[3].fX, 4 * sizeof(SkPoint));
+            chop_mono_cubic_at_y(tmp2, clip.fTop, tmp);
+        }
+
         // tmp[3, 4].fY should all be to the below clip.fTop.
-        // Since we can't trust the numerics of
-        // the chopper, we force those conditions now
+        // Since we can't trust the numerics of the chopper, we force those conditions now
         tmp[3].fY = clip.fTop;
         clamp_ge(tmp[4].fY, clip.fTop);
 
diff --git a/tests/PathTest.cpp b/tests/PathTest.cpp
index 44b6786019..8f98e6abaa 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -4129,6 +4129,21 @@ public:
     }
 };
 
+static void test_crbug_629455(skiatest::Reporter* reporter) {
+    SkPath path;
+    path.moveTo(0, 0);
+    path.cubicTo(SkBits2Float(0xcdcdcd00), SkBits2Float(0xcdcdcdcd),
+                 SkBits2Float(0xcdcdcdcd), SkBits2Float(0xcdcdcdcd),
+                 SkBits2Float(0x423fcdcd), SkBits2Float(0x40ed9341));
+//  AKA: cubicTo(-4.31596e+08f, -4.31602e+08f, -4.31602e+08f, -4.31602e+08f, 47.951f, 7.42423f);
+    path.lineTo(0, 0);
+
+    auto surface = SkSurface::MakeRasterN32Premul(100, 100);
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    surface->getCanvas()->drawPath(path, paint);
+}
+
 static void test_interp(skiatest::Reporter* reporter) {
     SkPath p1, p2, out;
     REPORTER_ASSERT(reporter, p1.isInterpolatable(p2));
@@ -4177,6 +4192,7 @@ DEF_TEST(PathContains, reporter) {
 }
 
 DEF_TEST(Paths, reporter) {
+    test_crbug_629455(reporter);
     test_fuzz_crbug_627414(reporter);
     test_path_crbug364224();