Address precision issue in circle blur effect

gm/blurredclippedcircle.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkBlurMaskFilter.h"
+#include "SkColorFilter.h"
+#include "SkPaint.h"
+#include "SkRRect.h"
+
+namespace skiagm {
+
+// This GM reproduces the precision artifacts seen in crbug.com/560651.
+// It draws a largish blurred circle with its center clipped out.
+class BlurredClippedCircleGM : public GM {
+public:
+    BlurredClippedCircleGM() {
+        this->setBGColor(sk_tool_utils::color_to_565(0xFFCCCCCC));
+    }
+
+protected:
+
+    SkString onShortName() override {
+        return SkString("blurredclippedcircle");
+    }
+
+    SkISize onISize() override {
+        return SkISize::Make(kWidth, kHeight);
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        SkPaint whitePaint;
+        whitePaint.setColor(SK_ColorWHITE);
+        whitePaint.setXfermode(SkXfermode::Create(SkXfermode::kSrc_Mode))->unref();
+        whitePaint.setAntiAlias(true);
+
+        // This scale exercises precision limits in the circle blur effect (crbug.com/560651)
+        static const float kScale = 2.0f;
+        canvas->scale(kScale, kScale);
+
+        canvas->save();
+            SkRect clipRect1 = SkRect::MakeLTRB(0, 0,
+                                                SkIntToScalar(kWidth), SkIntToScalar(kHeight));
+
+            canvas->clipRect(clipRect1, SkRegion::kIntersect_Op, false);
+
+            canvas->save();
+
+                canvas->clipRect(clipRect1, SkRegion::kIntersect_Op, false);
+                canvas->drawRect(clipRect1, whitePaint);
+
+                canvas->save();
+
+                    SkRect clipRect2 = SkRect::MakeLTRB(8, 8, 288, 288);
+                    SkRRect clipRRect = SkRRect::MakeOval(clipRect2);
+                    canvas->clipRRect(clipRRect, SkRegion::kDifference_Op, true);
+
+                    SkRect r = SkRect::MakeLTRB(4, 4, 292, 292);
+                    SkRRect rr = SkRRect::MakeOval(r);
+
+                    SkPaint paint;
+
+                    paint.setMaskFilter(SkBlurMaskFilter::Create(
+                                            kNormal_SkBlurStyle,
+                                            1.366025f,
+                                            SkBlurMaskFilter::kHighQuality_BlurFlag))->unref();
+                    paint.setColorFilter(SkColorFilter::CreateModeFilter(
+                                             SK_ColorRED,
+                                             SkXfermode::kSrcIn_Mode))->unref();
+                    paint.setAntiAlias(true);
+
+                    canvas->drawRRect(rr, paint);
+
+                canvas->restore();
+            canvas->restore();
+        canvas->restore();
+    }
+
+private:
+    static const int kWidth = 1164;
+    static const int kHeight = 802;
+
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+DEF_GM(return new BlurredClippedCircleGM;)
+}