GrTessellator: missing intersection rewind fix.

Some "missing" intersections (see
https://skia.googlesource.com/skia/+/89042d5f13a56d6b663657aa58f17593123a344e)
cause the active edge list to go out of order. In that case, we need
to rewind the active list, just as we do before edge splitting for
regular intersections.

BUG=860453

Change-Id: I1f7b32157a73b427a4fd94c14c1eb440f26c0743
Reviewed-on: https://skia-review.googlesource.com/141038
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>

2 files changed, 24 insertions, 0 deletions

diff --git a/src/gpu/GrTessellator.cpp b/src/gpu/GrTessellator.cpp
index 78616d4e2f..3424ee3f91 100644
--- a/src/gpu/GrTessellator.cpp
+++ b/src/gpu/GrTessellator.cpp
@@ -1110,21 +1110,28 @@ bool intersect_edge_pair(Edge* left, Edge* right, EdgeList* activeEdges, Vertex*
     if (!left->fTop || !left->fBottom || !right->fTop || !right->fBottom) {
         return false;
     }
+    if (left->fTop == right->fTop || left->fBottom == right->fBottom) {
+        return false;
+    }
     if (c.sweep_lt(left->fTop->fPoint, right->fTop->fPoint)) {
         if (!left->isLeftOf(right->fTop)) {
+            rewind(activeEdges, current, right->fTop, c);
             return split_edge(left, right->fTop, activeEdges, current, c, alloc);
         }
     } else {
         if (!right->isRightOf(left->fTop)) {
+            rewind(activeEdges, current, left->fTop, c);
             return split_edge(right, left->fTop, activeEdges, current, c, alloc);
         }
     }
     if (c.sweep_lt(right->fBottom->fPoint, left->fBottom->fPoint)) {
         if (!left->isLeftOf(right->fBottom)) {
+            rewind(activeEdges, current, right->fBottom, c);
             return split_edge(left, right->fBottom, activeEdges, current, c, alloc);
         }
     } else {
         if (!right->isRightOf(left->fBottom)) {
+            rewind(activeEdges, current, left->fBottom, c);
             return split_edge(right, left->fBottom, activeEdges, current, c, alloc);
         }
     }
diff --git a/tests/TessellatingPathRendererTests.cpp b/tests/TessellatingPathRendererTests.cpp
index 2891131f90..4b3b321f17 100644
--- a/tests/TessellatingPathRendererTests.cpp
+++ b/tests/TessellatingPathRendererTests.cpp
@@ -584,6 +584,22 @@ static SkPath create_path_40() {
     return path;
 }
 
+// Reduction from crbug.com/860453. Tests a case where a "missing" intersection
+// requires the active edge list to go out-of-order.
+static SkPath create_path_41() {
+    SkPath path;
+    path.moveTo(72154931603311689728.0,   330.95965576171875);
+    path.lineTo(24053266013925408768.0,       78.11376953125);
+    path.lineTo(1.2031099003292404941e+20,  387.168731689453125);
+    path.lineTo(68859835992355373056.0,   346.55047607421875);
+    path.lineTo(76451708695451009024.0,     337.780029296875);
+    path.moveTo(-20815817797613387776.0, 18065700622522384384.0);
+    path.lineTo(-72144121204987396096.0,  142.855804443359375);
+    path.lineTo(72144121204987396096.0,  325.184783935546875);
+    path.lineTo(1.2347242901040791552e+20, 18065700622522384384.0);
+    return path;
+}
+
 static std::unique_ptr<GrFragmentProcessor> create_linear_gradient_processor(GrContext* ctx) {
 
     SkPoint pts[2] = { {0, 0}, {1, 1} };
@@ -684,4 +700,5 @@ DEF_GPUTEST_FOR_ALL_CONTEXTS(TessellatingPathRendererTests, reporter, ctxInfo) {
     test_path(ctx, rtc.get(), create_path_38(), SkMatrix(), GrAAType::kCoverage);
     test_path(ctx, rtc.get(), create_path_39());
     test_path(ctx, rtc.get(), create_path_40());
+    test_path(ctx, rtc.get(), create_path_41(), SkMatrix(), GrAAType::kCoverage);
 }