tweak tolerance again for cubics

Bug: 845489
Bug: skia:7995
Change-Id: I05554377bd5630b7134864b6db282358613f1030
Reviewed-on: https://skia-review.googlesource.com/129721
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Mike Reed <reed@google.com>

2 files changed, 17 insertions, 5 deletions

diff --git a/src/core/SkScan_Path.cpp b/src/core/SkScan_Path.cpp
index 1854a7edd7..90a2230526 100644
--- a/src/core/SkScan_Path.cpp
+++ b/src/core/SkScan_Path.cpp
@@ -567,7 +567,9 @@ static bool clip_to_limit(const SkRegion& orig, SkRegion* reduced) {
 //
 // This value has been determined trial and error: pick the smallest value (after the 0.5) that
 // fixes any problematic cases (e.g. crbug.com/844457)
-static const double kConservativeRoundBias = 0.5 + 1.0 / SK_FDot6One;
+// NOTE: cubics appear to be the main reason for needing this slop. If we could (perhaps) have a
+// more accurate walker for cubics, we may be able to reduce this fudge factor.
+static const double kConservativeRoundBias = 0.5 + 1.5 / SK_FDot6One;
 
 /**
  *  Round the value down. This is used to round the top and left of a rectangle,
diff --git a/tests/ClipCubicTest.cpp b/tests/ClipCubicTest.cpp
index 427e753322..ca2f62314d 100644
--- a/tests/ClipCubicTest.cpp
+++ b/tests/ClipCubicTest.cpp
@@ -212,13 +212,23 @@ DEF_TEST(test_fuzz_crbug_698714, reporter) {
     canvas->drawPath(path, paint);
 }
 
-DEF_TEST(cubic_scan_error_crbug_844457, reporter) {
+DEF_TEST(cubic_scan_error_crbug_844457_and_845489, reporter) {
     auto surface(SkSurface::MakeRasterN32Premul(100, 100));
+    SkCanvas* canvas = surface->getCanvas();
+    SkPaint p;
 
     SkPath path;
     path.moveTo(-30/64.0, -31/64.0);
     path.cubicTo(-31/64.0, -31/64,-31/64.0, -31/64,-31/64.0, 100);
-    path.lineTo(100,100);
-
-    surface->getCanvas()->drawPath(path, SkPaint());
+    path.lineTo(100, 100);
+    canvas->drawPath(path, p);
+
+    // May need to define SK_RASTERIZE_EVEN_ROUNDING to trigger the need for this test
+    path.reset();
+    path.moveTo(-30/64.0f,             -31/64.0f + 1/256.0f);
+    path.cubicTo(-31/64.0f + 1/256.0f, -31/64.0f + 1/256.0f,
+                 -31/64.0f + 1/256.0f, -31/64.0f + 1/256.0f,
+                 -31/64.0f + 1/256.0f, 100);
+    path.lineTo(100, 100);
+    canvas->drawPath(path, p);
 }