Reland "GrTessellator: hang fix."

This is a reland of 050c86768a2c24c62655f53ef9b685d40477eccb

Original change's description:
> GrTessellator: hang fix.
> 
> Some edges are not coincident with their own endpoints (because floating
> point). If this happens for an edge which is a right-enclosing-edge
> during the Bentley-Ottman simplify() pass, we end up an infinite loop
> attempting to split the edge, since the edge is never to the right of its
> endpoint.
> 
> The easiest fix is to simply remove the right-enclosing-edge splitting
> code. This code was originally added before we had proper
> active-edge-list rewinding, and should no longer be necessary.
> 
> BUG=802896
> 
> Change-Id: Id9f2942b73f01152af8c0088e8c6b1389891d827
> Reviewed-on: https://skia-review.googlesource.com/116920
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Commit-Queue: Stephen White <senorblanco@chromium.org>

Bug: 802896
Change-Id: I3e48346a8a358ae7d481299a586003e817a519ca
Reviewed-on: https://skia-review.googlesource.com/117121
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>

2 files changed, 22 insertions, 6 deletions

diff --git a/src/gpu/GrTessellator.cpp b/src/gpu/GrTessellator.cpp
index 00e5c8a21c..b8ec6551c9 100644
--- a/src/gpu/GrTessellator.cpp
+++ b/src/gpu/GrTessellator.cpp
@@ -1421,12 +1421,6 @@ bool simplify(VertexList* mesh, Comparator& c, SkArenaAlloc& alloc) {
             LOG("\nvertex %g: (%g,%g), alpha %d\n", v->fID, v->fPoint.fX, v->fPoint.fY, v->fAlpha);
             restartChecks = false;
             find_enclosing_edges(v, &activeEdges, &leftEnclosingEdge, &rightEnclosingEdge);
-            if (rightEnclosingEdge && !rightEnclosingEdge->isRightOf(v)) {
-                split_edge(rightEnclosingEdge, v, &activeEdges, &v, c, alloc);
-                restartChecks = true;
-                continue;
-            }
-            SkASSERT(!rightEnclosingEdge || rightEnclosingEdge->isRightOf(v));
             v->fLeftEnclosingEdge = leftEnclosingEdge;
             v->fRightEnclosingEdge = rightEnclosingEdge;
             if (v->fFirstEdgeBelow) {
diff --git a/tests/TessellatingPathRendererTests.cpp b/tests/TessellatingPathRendererTests.cpp
index 451391762d..035b3fe323 100644
--- a/tests/TessellatingPathRendererTests.cpp
+++ b/tests/TessellatingPathRendererTests.cpp
@@ -439,6 +439,27 @@ static SkPath create_path_29() {
     return path;
 }
 
+// A path which hangs during simplification. It produces an edge which is
+// to the left of its own endpoints, which causes an infinte loop in the
+// right-enclosing-edge splitting.
+static SkPath create_path_30() {
+    SkPath path;
+    path.moveTo(0.75001740455627441406,     23.051967620849609375);
+    path.lineTo(5.8471612930297851562,      22.731662750244140625);
+    path.lineTo(10.749670028686523438,      22.253145217895507812);
+    path.lineTo(13.115868568420410156,      22.180681228637695312);
+    path.lineTo(15.418928146362304688,      22.340015411376953125);
+    path.lineTo(  17.654022216796875,       22.82159423828125);
+    path.lineTo(19.81632232666015625,       23.715869903564453125);
+    path.lineTo(40,                         0);
+    path.lineTo(5.5635203441547955577e-15,  0);
+    path.lineTo(5.5635203441547955577e-15,  47);
+    path.lineTo(-1.4210854715202003717e-14, 21.713298797607421875);
+    path.lineTo(0.75001740455627441406,     21.694292068481445312);
+    path.lineTo(0.75001740455627441406,     23.051967620849609375);
+    return path;
+}
+
 static std::unique_ptr<GrFragmentProcessor> create_linear_gradient_processor(GrContext* ctx) {
 
     SkPoint pts[2] = { {0, 0}, {1, 1} };
@@ -529,5 +550,6 @@ DEF_GPUTEST_FOR_ALL_CONTEXTS(TessellatingPathRendererTests, reporter, ctxInfo) {
     test_path(ctx, rtc.get(), create_path_27(), SkMatrix(), GrAAType::kCoverage);
     test_path(ctx, rtc.get(), create_path_28(), SkMatrix(), GrAAType::kCoverage);
     test_path(ctx, rtc.get(), create_path_29());
+    test_path(ctx, rtc.get(), create_path_30());
 }
 #endif