SkScan_Antihair: assert in debug and potentialy lost last pixels

tests/RectTest.cpp

Index: tests/RectTest.cpp
diff --git a/tests/RectTest.cpp b/tests/RectTest.cpp
index be77a87406168a4bae5463c96c38bf8d114c4bfa..1ced83f7e362defdca048bcd8b0d8fa1152c32c7 100644
--- a/tests/RectTest.cpp
+++ b/tests/RectTest.cpp
@@ -46,6 +46,45 @@ static void test_stroke_width_clipping(skiatest::Reporter* reporter) {
     REPORTER_ASSERT(reporter, has_green_pixels(bm));
 }
 
+static void test_skbug4406(skiatest::Reporter* reporter) {
+    SkBitmap bm;
+    bm.allocN32Pixels(10, 10);
+    bm.eraseColor(SK_ColorTRANSPARENT);
+
+    SkCanvas canvas(bm);
+    const SkRect r = { 1.5f, 1, 3.5f, 3 };
+    // draw filled green rect first
+    SkPaint paint;
+    paint.setStyle(SkPaint::kFill_Style);
+    paint.setColor(0xff00ff00);
+    paint.setStrokeWidth(1);
+    paint.setAntiAlias(true);
+    canvas.drawRect(r, paint);
+
+    // paint black with stroke rect (that asserts in bug 4406)
+    // over the filled rect, it should cover it
+    paint.setStyle(SkPaint::kStroke_Style);
+    paint.setColor(0xff000000);
+    paint.setStrokeWidth(1);
+    canvas.drawRect(r, paint);
+    REPORTER_ASSERT(reporter, !has_green_pixels(bm));
+
+    // do it again with thinner stroke
+    paint.setStyle(SkPaint::kFill_Style);
+    paint.setColor(0xff00ff00);
+    paint.setStrokeWidth(1);
+    paint.setAntiAlias(true);
+    canvas.drawRect(r, paint);
+    // paint black with stroke rect (that asserts in bug 4406)
+    // over the filled rect, it doesnt cover it completelly with thinner stroke
+    paint.setStyle(SkPaint::kStroke_Style);
+    paint.setColor(0xff000000);
+    paint.setStrokeWidth(0.99f);
+    canvas.drawRect(r, paint);
+    REPORTER_ASSERT(reporter, has_green_pixels(bm));
+}
+
 DEF_TEST(Rect, reporter) {
     test_stroke_width_clipping(reporter);
+    test_skbug4406(reporter);
 }