Fix index overflow check for rewriting fans as triangles.

Not only could the old test cause int overflow, it was just wrong.

Bug: skia:8085
Change-Id: Id6b81f4aa1b115f0dbfd2266aee8fab5d5d30aee
Reviewed-on: https://skia-review.googlesource.com/124779
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

2 files changed, 3 insertions, 3 deletions

diff --git a/src/core/SkVertices.cpp b/src/core/SkVertices.cpp
index c945fc00e9..abe2b4ce67 100644
--- a/src/core/SkVertices.cpp
+++ b/src/core/SkVertices.cpp
@@ -42,7 +42,7 @@ struct SkVertices::Sizes {
                 numFanTris = vertexCount - 2;
                 // By forcing this to become indexed we are adding a constraint to the maximum
                 // number of vertices.
-                if (3 * numFanTris > (SK_MaxU16 + 1)) {
+                if (vertexCount > (SK_MaxU16 + 1)) {
                     sk_bzero(this, sizeof(*this));
                     return;
                 }
diff --git a/tests/VerticesTest.cpp b/tests/VerticesTest.cpp
index 5bcb11f1d3..59d06472ac 100644
--- a/tests/VerticesTest.cpp
+++ b/tests/VerticesTest.cpp
@@ -91,13 +91,13 @@ DEF_TEST(Vertices, reporter) {
     {
         // This has the maximum number of vertices to be rewritten as indexed triangles without
         // overflowing a 16bit index.
-        SkVertices::Builder builder(SkVertices::kTriangleFan_VertexMode, 21847, 0,
+        SkVertices::Builder builder(SkVertices::kTriangleFan_VertexMode, SK_MaxU16 + 1, 0,
                                     SkVertices::kHasColors_BuilderFlag);
         REPORTER_ASSERT(reporter, builder.isValid());
     }
     {
         // This has too many to be rewritten.
-        SkVertices::Builder builder(SkVertices::kTriangleFan_VertexMode, 21848, 0,
+        SkVertices::Builder builder(SkVertices::kTriangleFan_VertexMode, SK_MaxU16 + 2, 0,
                                     SkVertices::kHasColors_BuilderFlag);
         REPORTER_ASSERT(reporter, !builder.isValid());
     }