Analytic AntiAlias for Convex Shapes

gm/addarc.cpp

Index: gm/addarc.cpp
diff --git a/gm/addarc.cpp b/gm/addarc.cpp
index 9280140794af70413a949847c64fde74d9171efd..bb973089c98bcf541ebaeaad44cdf5c153fe840a 100644
--- a/gm/addarc.cpp
+++ b/gm/addarc.cpp
@@ -163,6 +163,54 @@ private:
 };
 DEF_GM( return new StrokeCircleGM; )
 
+// Fill circles and rotate them to test our Analytic Anti-Aliasing
+class FillCircleGM : public skiagm::GM {
+public:
+    FillCircleGM() : fRotate(0) {}
+
+protected:
+    SkString onShortName() override { return SkString("fillcircle"); }
+
+    SkISize onISize() override { return SkISize::Make(520, 520); }
+
+    void onDraw(SkCanvas* canvas) override {
+        canvas->scale(20, 20);
+        canvas->translate(13, 13);
+
+        SkPaint paint;
+        paint.setAntiAlias(true);
+        paint.setStyle(SkPaint::kStroke_Style);
+        paint.setStrokeWidth(SK_Scalar1 / 2);
+
+        const SkScalar delta = paint.getStrokeWidth() * 3 / 2;
+        SkRect r = SkRect::MakeXYWH(-12, -12, 24, 24);
+        SkRandom rand;
+
+        SkScalar sign = 1;
+        while (r.width() > paint.getStrokeWidth() * 2) {
+            SkAutoCanvasRestore acr(canvas, true);
+            canvas->rotate(fRotate * sign);
+
+            paint.setColor(sk_tool_utils::color_to_565(rand.nextU() | (0xFF << 24)));
+            paint.setStyle(SkPaint::kFill_Style);
+            canvas->drawOval(r, paint);
+            r.inset(delta, delta);
+            sign = -sign;
+        }
+    }
+
+    bool onAnimate(const SkAnimTimer& timer) override {
+        fRotate = timer.scaled(60, 360);
+        return true;
+    }
+
+private:
+    SkScalar fRotate;
+
+    typedef skiagm::GM INHERITED;
+};
+DEF_GM( return new FillCircleGM; )
+
 //////////////////////
 
 static void html_canvas_arc(SkPath* path, SkScalar x, SkScalar y, SkScalar r, SkScalar start,