GrTessellator: fix for ping-pong split fuzzer hang.

Change 3b5a3fa8b1c11d4bd4499b040311f4c3553ebf8c introduced support for
splitting on out-of-range intersections. However, this is only necessary
for correctness when the edge is nearly-flat (the top and bottom
points only differ by 1/2 machine epsilon in the primary sort criterion).
In other cases, it can cause repeated splitting and re-merging of edges,
as the intersection code (being approximate and not exact) may produce a
ping-pong set of intersections.

The fix is to support out-of-range intersections only if they differ by
1/2 machine epsilon. This also generalizes the
out_of_range_and_collinear() check, so it was removed.

Bug: 838978
Change-Id: I134f7eff3f15707e0d68de11c55f7fadce4ff8e7
Reviewed-on: https://skia-review.googlesource.com/130448
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/tests/TessellatingPathRendererTests.cpp b/tests/TessellatingPathRendererTests.cpp
index 00f43985dd..a2dc95986e 100644
--- a/tests/TessellatingPathRendererTests.cpp
+++ b/tests/TessellatingPathRendererTests.cpp
@@ -502,6 +502,16 @@ static SkPath create_path_33() {
     return path;
 }
 
+// From crbug.com/844873. Hangs repeatedly splitting alternate vertices.
+static SkPath create_path_34() {
+    SkPath path;
+    path.moveTo(10, -1e+20f);
+    path.lineTo(11, 25000);
+    path.lineTo(10, 25000);
+    path.lineTo(11, 25010);
+    return path;
+}
+
 static std::unique_ptr<GrFragmentProcessor> create_linear_gradient_processor(GrContext* ctx) {
 
     SkPoint pts[2] = { {0, 0}, {1, 1} };
@@ -595,5 +605,6 @@ DEF_GPUTEST_FOR_ALL_CONTEXTS(TessellatingPathRendererTests, reporter, ctxInfo) {
     test_path(ctx, rtc.get(), create_path_31(), SkMatrix(), GrAAType::kCoverage);
     test_path(ctx, rtc.get(), create_path_32());
     test_path(ctx, rtc.get(), create_path_33());
+    test_path(ctx, rtc.get(), create_path_34());
 }
 #endif