GrTessellator: fix intersection above the first vertex.

Handle the case where the an intersection falls not only above both
edge endpoints, but above the first vertex in the mesh. This requires
passing the mesh into check_for_intersection(), in order to modify the
head. We also need to rewind the mesh after insertion, since we need
to rewind to the newly-inserted vertex.

This also cleans up vertex ID computation a little (for logging), so
that vertices before the first vertex or after the last have a
reasonable ID. It also cleans up the intersection-on-endpoint 
special cases by refactoring the calls to split_edge().

BUG=730687

Change-Id: Idea736eca7b7c3c5d8a470b1373a16ad8e649e80
Reviewed-on: https://skia-review.googlesource.com/19069
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/tests/TessellatingPathRendererTests.cpp b/tests/TessellatingPathRendererTests.cpp
index 7871193942..dd3b07ad99 100644
--- a/tests/TessellatingPathRendererTests.cpp
+++ b/tests/TessellatingPathRendererTests.cpp
@@ -314,6 +314,19 @@ static SkPath create_path_19() {
     return path;
 }
 
+// From clusterfuzz-testcase-minimized-6735316361936896
+// FIXME: [add description here]
+
+static SkPath create_path_20() {
+    SkPath path;
+    path.moveTo(           2822128.5,  235.026336669921875);
+    path.lineTo(          2819349.25, 235.3623504638671875);
+    path.lineTo(          -340558688, 23.83478546142578125);
+    path.lineTo(          -340558752, 25.510419845581054688);
+    path.lineTo(          -340558720, 27.18605804443359375);
+    return path;
+}
+
 static sk_sp<GrFragmentProcessor> create_linear_gradient_processor(GrContext* ctx) {
     SkPoint pts[2] = { {0, 0}, {1, 1} };
     SkColor colors[2] = { SK_ColorGREEN, SK_ColorBLUE };
@@ -390,5 +403,6 @@ DEF_GPUTEST_FOR_ALL_CONTEXTS(TessellatingPathRendererTests, reporter, ctxInfo) {
     test_path(ctx, rtc.get(), create_path_17(), nonInvertibleMatrix, GrAAType::kCoverage, fp);
     test_path(ctx, rtc.get(), create_path_18());
     test_path(ctx, rtc.get(), create_path_19());
+    test_path(ctx, rtc.get(), create_path_20(), SkMatrix(), GrAAType::kCoverage);
 }
 #endif