Fix quickReject computation for blurs

gm/blurquickreject.cpp

+/*
+ * Copyright 2013 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 "SkCanvas.h"
+#include "SkBlurMaskFilter.h"
+
+// This GM tests out the quick reject bounds of the blur mask filter. It draws
+// four blurred rects around a central clip. The blurred rect geometry outset
+// by the blur radius does not overlap the clip rect so, if the blur clipping
+// just uses the radius, they will be clipped out (and the result will differ
+// from the result if quick reject were disabled. If the blur clipping uses
+// the correct 3 sigma bound then the images with and without quick rejecting
+// will be the same.
+class BlurQuickRejectGM : public skiagm::GM {
+public:
+    BlurQuickRejectGM() {}
+
+protected:
+    virtual SkString onShortName() SK_OVERRIDE {
+        return SkString("blurquickreject");
+    }
+
+    virtual SkISize onISize() SK_OVERRIDE {
+        return SkISize::Make(kWidth, kHeight);
+    }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        static const SkScalar kBlurRadius = SkIntToScalar(20);
+        static const SkScalar kBoxSize = SkIntToScalar(100);
+
+        SkRect clipRect = SkRect::MakeXYWH(0, 0, kBoxSize, kBoxSize);
+        SkRect blurRects[] = {
+            { -kBoxSize - (kBlurRadius+1), 0, -(kBlurRadius+1), kBoxSize },
+            { 0, -kBoxSize - (kBlurRadius+1), kBoxSize, -(kBlurRadius+1) },
+            { kBoxSize+kBlurRadius+1, 0, 2*kBoxSize+kBlurRadius+1, kBoxSize },
+            { 0, kBoxSize+kBlurRadius+1, kBoxSize, 2*kBoxSize+kBlurRadius+1 }
+        };
+        SkColor colors[] = {
+            SK_ColorRED,
+            SK_ColorGREEN,
+            SK_ColorBLUE,
+            SK_ColorYELLOW,
+        };
+        SkASSERT(SK_ARRAY_COUNT(colors) == SK_ARRAY_COUNT(blurRects));
+
+        SkPaint hairlinePaint;
+        hairlinePaint.setStyle(SkPaint::kStroke_Style);
+        hairlinePaint.setColor(SK_ColorWHITE);
+        hairlinePaint.setStrokeWidth(0);
+
+        SkPaint blurPaint;
+        blurPaint.setFilterBitmap(true);
+        SkMaskFilter* mf = SkBlurMaskFilter::Create(kBlurRadius,
+                                                    SkBlurMaskFilter::kNormal_BlurStyle);
+        blurPaint.setMaskFilter(mf)->unref();
+
+        canvas->clear(SK_ColorBLACK);
+        canvas->save();
+        canvas->translate(kBoxSize, kBoxSize);
+        canvas->drawRect(clipRect, hairlinePaint);
+        canvas->clipRect(clipRect);
+        for (int i = 0; i < SK_ARRAY_COUNT(blurRects); ++i) {
+            blurPaint.setColor(colors[i]);
+            canvas->drawRect(blurRects[i], blurPaint);
+            canvas->drawRect(blurRects[i], hairlinePaint);
+        }
+        canvas->restore();
+    }
+
+private:
+    static const int kWidth = 300;
+    static const int kHeight = 300;
+
+    typedef GM INHERITED;
+};
+
+DEF_GM( return new BlurQuickRejectGM(); )