Compute slope using fSnappedY

If we use the oldy and dy directly as we did previously, the slope could
be very different from (newSnappedX - fSnappedX) / (newSnappedY -
fSnappedY) in the updateLine when the edge made a lot of updates with
small dy but large dx. That will cause bug skia:5995

BUG=skia:5995

Change-Id: If521976ed87195dfea5961afd58bedb98447c568
Reviewed-on: https://skia-review.googlesource.com/5269
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/tests/PathTest.cpp b/tests/PathTest.cpp
index f064a16f77..9be3976dae 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -242,6 +242,19 @@ static void test_path_crbugskia2820(skiatest::Reporter* reporter) {//GrContext*
     stroke.applyToPath(&path, path);
 }
 
+static void test_path_crbugskia5995() {
+    auto surface(SkSurface::MakeRasterN32Premul(500, 500));
+    SkCanvas* canvas = surface->getCanvas();
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    SkPath path;
+    path.moveTo(SkBits2Float(0x40303030), SkBits2Float(0x3e303030));  // 2.75294f, 0.172059f
+    path.quadTo(SkBits2Float(0x41d63030), SkBits2Float(0x30303030), SkBits2Float(0x41013030),
+            SkBits2Float(0x00000000));  // 26.7735f, 6.40969e-10f, 8.07426f, 0
+    path.moveTo(SkBits2Float(0x00000000), SkBits2Float(0x00000000));  // 0, 0
+    canvas->drawPath(path, paint);
+}
+
 static void make_path0(SkPath* path) {
     // from  *  https://code.google.com/p/skia/issues/detail?id=1706
 
@@ -4528,6 +4541,7 @@ DEF_TEST(Paths, reporter) {
     test_dump(reporter);
     test_path_crbug389050(reporter);
     test_path_crbugskia2820(reporter);
+    test_path_crbugskia5995();
     test_skbug_3469(reporter);
     test_skbug_3239(reporter);
     test_bounds_crbug_513799(reporter);