Fix quickReject computation for blurs

src/effects/SkBlurMaskFilter.cpp

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBlurMaskFilter.h"
 #include "SkBlurMask.h"
 #include "SkFlattenableBuffers.h"
 #include "SkMaskFilter.h"
 #include "SkBounder.h"
 #include "SkRasterClip.h"
 #include "SkRTConf.h"
 #include "SkStringUtils.h"
 
+const SkScalar SkBlurMaskFilter::kBLUR_SIGMA_SCALE = SkFloatToScalar(0.6f);
+const SkScalar SkBlurMaskFilter::kBlurRadiusFudgeFactor = SkFloatToScalar(.57735f);
+
 class SkBlurMaskFilterImpl : public SkMaskFilter {
 public:
     SkBlurMaskFilterImpl(SkScalar radius, SkBlurMaskFilter::BlurStyle,
                          uint32_t flags);
 
     // overrides from SkMaskFilter
     virtual SkMask::Format getFormat() const SK_OVERRIDE;
     virtual bool filterMask(SkMask* dst, const SkMask& src, const SkMatrix&,
                             SkIPoint* margin) const SK_OVERRIDE;
 
@@ skipping 265 matching lines @@
         }
     }
     patch->fMask.fBounds.offsetTo(0, 0);
     patch->fOuterRect = dstM.fBounds;
     patch->fCenter = center;
     return kTrue_FilterReturn;
 }
 
 void SkBlurMaskFilterImpl::computeFastBounds(const SkRect& src,
                                              SkRect* dst) const {
-    dst->set(src.fLeft - fRadius, src.fTop - fRadius,
-             src.fRight + fRadius, src.fBottom + fRadius);
+    SkScalar gpuPad, rasterPad;
+
+    {
+        // GPU path
+        SkScalar sigma = SkScalarMul(fRadius, SkBlurMaskFilter::kBLUR_SIGMA_SCALE);
+        gpuPad = sigma * 3.0f;
+    }
+
+    {
+        // raster path
+        SkScalar radius = SkScalarMul(fRadius, SkBlurMaskFilter::kBlurRadiusFudgeFactor);
+ 
+        radius = (radius + .5f) * 2.f;
+
+        rasterPad = SkIntToScalar(SkScalarRoundToInt(radius * 3)/2);
+    }
+
+    SkScalar pad = SkMaxScalar(gpuPad, rasterPad);
+
+    dst->set(src.fLeft  - pad, src.fTop    - pad,
+             src.fRight + pad, src.fBottom + pad);
 }
 
 SkBlurMaskFilterImpl::SkBlurMaskFilterImpl(SkFlattenableReadBuffer& buffer)
         : SkMaskFilter(buffer) {
     fRadius = buffer.readScalar();
     fBlurStyle = (SkBlurMaskFilter::BlurStyle)buffer.readInt();
     fBlurFlags = buffer.readUInt() & SkBlurMaskFilter::kAll_BlurFlag;
     SkASSERT(fRadius >= 0);
     SkASSERT((unsigned)fBlurStyle < SkBlurMaskFilter::kBlurStyleCount);
 }
@@ skipping 46 matching lines @@
     } else {
         str->append("None");
     }
     str->append("))");
 }
 #endif
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkBlurMaskFilter)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkBlurMaskFilterImpl)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END