skipRect should only work for lines (not quads or cubics)

The added unit test shows that we'll trigger SkASSERT failure if we
forgot to check that the edges are lines (instead of quads or cubics).
Similar to skia:7015, this bug is not triggered in our production
because we don't use DAA for convex paths by default. The skipRect is
an optimization just for convex paths.

Bug: skia:7051
Change-Id: Id87ce2d452ede0db9a48425541f473af19ee0572
Reviewed-on: https://skia-review.googlesource.com/48045
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>

2 files changed, 14 insertions, 2 deletions

diff --git a/src/core/SkScan_DAAPath.cpp b/src/core/SkScan_DAAPath.cpp
index a12b6da9b0..9250d02f07 100644
--- a/src/core/SkScan_DAAPath.cpp
+++ b/src/core/SkScan_DAAPath.cpp
@@ -173,8 +173,9 @@ void gen_alpha_deltas(const SkPath& path, const SkRegion& clipRgn, Deltas& resul
             SkBezier* lb = list[i];
             SkBezier* rb = list[i + 1];
 
-            bool lDX0 = lb->fP0.fX == lb->fP1.fX;
-            bool rDX0 = rb->fP0.fX == rb->fP1.fX;
+            // fCount == 2 ensures that lb and rb are lines instead of quads or cubics.
+            bool lDX0 = lb->fP0.fX == lb->fP1.fX && lb->fCount == 2;
+            bool rDX0 = rb->fP0.fX == rb->fP1.fX && rb->fCount == 2;
             if (!lDX0 || !rDX0) { // make sure that the edges are vertical
                 continue;
             }
diff --git a/tests/PathTest.cpp b/tests/PathTest.cpp
index 8c629d9485..4fb559b323 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -4482,6 +4482,16 @@ static void test_skbug_7015() {
     test_draw_AA_path(500, 500, path);
 }
 
+static void test_skbug_7051() {
+    SkPath path;
+    path.moveTo(10, 10);
+    path.cubicTo(10, 20, 10, 30, 30, 30);
+    path.lineTo(50, 20);
+    path.lineTo(50, 10);
+    path.close();
+    test_draw_AA_path(100, 100, path);
+}
+
 #endif
 
 static void test_interp(skiatest::Reporter* reporter) {
@@ -4559,6 +4569,7 @@ DEF_TEST(Paths, reporter) {
 #if !defined(SK_SUPPORT_LEGACY_DELTA_AA)
     test_skbug_6947();
     test_skbug_7015();
+    test_skbug_7051();
 #endif
 
     SkSize::Make(3, 4);