Quality and performance fixes for AA tessellating path renderer.

Use quads rather than triangles for the edge geometry. This allows
us to perform a simpler edge categorization (see below). It also
improves performance by reducing the number of edges processed during
the simplify and tessellate steps.

Label AA edges as three types: inner, outer, and connector. This
results in correct alpha values for intersected edges, even when
the top or bottom vertex has been merged with a vertex on edges
of different types.

Changed the "collinear edges" sample from the concavepaths GM for a
"fast-foward" shape, which more clearly shows the problem being fixed
here. (The collinearity from the "collinear edges" was actually being
removed earlier up the stack, causing the path to become convex and
not exercise the concave path renderers anyway.)

NOTE: this will cause changes in the "concavepaths" GM results, and
minor pixel diffs in a number of other tests.

Change-Id: I6c2b0cdb35cda42b01cf1100621271fef5be35b0
Reviewed-on: https://skia-review.googlesource.com/6430
Reviewed-by: Stephan White <senorblanco@chromium.org>
Commit-Queue: Stephan White <senorblanco@chromium.org>

1 files changed, 9 insertions, 6 deletions

diff --git a/gm/concavepaths.cpp b/gm/concavepaths.cpp
index ad87d255ca..c68265b99f 100644
--- a/gm/concavepaths.cpp
+++ b/gm/concavepaths.cpp
@@ -80,15 +80,18 @@ void test_fish(SkCanvas* canvas, const SkPaint& paint) {
     canvas->restore();
 }
 
-// Collinear edges
-void test_collinear_edges(SkCanvas* canvas, const SkPaint& paint) {
+// Overlapping "Fast-forward" icon: tests coincidence of inner and outer
+// vertices generated by intersection.
+void test_fast_forward(SkCanvas* canvas, const SkPaint& paint) {
     SkPath path;
     canvas->save();
     canvas->translate(100, 100);
     path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
-    path.lineTo(SkIntToScalar(50), SkIntToScalar(20));
-    path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
-    path.lineTo(SkIntToScalar(50), SkIntToScalar(80));
+    path.lineTo(SkIntToScalar(60), SkIntToScalar(50));
+    path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
+    path.moveTo(SkIntToScalar(40), SkIntToScalar(20));
+    path.lineTo(SkIntToScalar(40), SkIntToScalar(80));
+    path.lineTo(SkIntToScalar(80), SkIntToScalar(50));
     canvas->drawPath(path, paint);
     canvas->restore();
 }
@@ -384,7 +387,7 @@ protected:
         test_bowtie(canvas, paint);
         test_fake_bowtie(canvas, paint);
         test_fish(canvas, paint);
-        test_collinear_edges(canvas, paint);
+        test_fast_forward(canvas, paint);
         test_hole(canvas, paint);
         test_star(canvas, paint);
         test_stairstep(canvas, paint);