Allow negative values in SkBlurImageFilter sigma.

src/effects/SkBlurImageFilter.cpp

Index: src/effects/SkBlurImageFilter.cpp
diff --git a/src/effects/SkBlurImageFilter.cpp b/src/effects/SkBlurImageFilter.cpp
index 8590400003eba2ffb8aae2eb255abcc00e207f0a..febc062a431c32203ea0f656cb45d7004c4efe78 100644
--- a/src/effects/SkBlurImageFilter.cpp
+++ b/src/effects/SkBlurImageFilter.cpp
@@ -23,15 +23,28 @@
 // raster paths.
 #define MAX_SIGMA SkIntToScalar(532)
 
+static SkVector mapSigma(const SkSize& localSigma, const SkMatrix& ctm) {
+    SkVector sigma = SkVector::Make(localSigma.width(), localSigma.height());
+    ctm.mapVectors(&sigma, 1);
+    sigma.fX = SkMinScalar(sigma.fX, MAX_SIGMA);
+    sigma.fY = SkMinScalar(sigma.fY, MAX_SIGMA);

[sugoi1, 2014/09/09 15:42:39]

Shouldn't this happen after line 37? What if sigma.fX is a very large negative
number?

Or why not just replace lines 29 to 37 by :
sigma.fX = SkMinScalar(SkScalarAbs(sigma.fX), MAX_SIGMA);
sigma.fY = SkMinScalar(SkScalarAbs(sigma.fY), MAX_SIGMA);

[Stephen White, 2014/09/09 16:03:59]

Good catch. Fixed.

+    if (sigma.fX < 0) {

[reed1, 2014/09/09 15:37:38]

SkScalarAbs() 

[Stephen White, 2014/09/09 15:48:15]

Done.

+        sigma.fX = -sigma.fX;
+    }
+
+    if (sigma.fY < 0) {
+        sigma.fY = -sigma.fY;
+    }
+    return sigma;
+}
+
 #ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
 SkBlurImageFilter::SkBlurImageFilter(SkReadBuffer& buffer)
   : INHERITED(1, buffer) {
     fSigma.fWidth = buffer.readScalar();
     fSigma.fHeight = buffer.readScalar();
     buffer.validate(SkScalarIsFinite(fSigma.fWidth) &&
-                    SkScalarIsFinite(fSigma.fHeight) &&
-                    (fSigma.fWidth >= 0) &&
-                    (fSigma.fHeight >= 0));
+                    SkScalarIsFinite(fSigma.fHeight));
 }
 #endif
 
@@ -177,10 +190,7 @@ bool SkBlurImageFilter::onFilterImage(Proxy* proxy,
     }
     dst->getBounds(&dstBounds);
 
-    SkVector sigma = SkVector::Make(fSigma.width(), fSigma.height());
-    ctx.ctm().mapVectors(&sigma, 1);
-    sigma.fX = SkMinScalar(sigma.fX, MAX_SIGMA);
-    sigma.fY = SkMinScalar(sigma.fY, MAX_SIGMA);
+    SkVector sigma = mapSigma(fSigma, ctx.ctm());
 
     int kernelSizeX, kernelSizeX3, lowOffsetX, highOffsetX;
     int kernelSizeY, kernelSizeY3, lowOffsetY, highOffsetY;
@@ -253,8 +263,7 @@ void SkBlurImageFilter::computeFastBounds(const SkRect& src, SkRect* dst) const
 bool SkBlurImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
                                        SkIRect* dst) const {
     SkIRect bounds = src;
-    SkVector sigma = SkVector::Make(fSigma.width(), fSigma.height());
-    ctm.mapVectors(&sigma, 1);
+    SkVector sigma = mapSigma(fSigma, ctm);
     bounds.outset(SkScalarCeilToInt(SkScalarMul(sigma.x(), SkIntToScalar(3))),
                   SkScalarCeilToInt(SkScalarMul(sigma.y(), SkIntToScalar(3))));
     if (getInput(0) && !getInput(0)->filterBounds(bounds, ctm, &bounds)) {
@@ -277,10 +286,7 @@ bool SkBlurImageFilter::filterImageGPU(Proxy* proxy, const SkBitmap& src, const
         return false;
     }
     GrTexture* source = input.getTexture();
-    SkVector sigma = SkVector::Make(fSigma.width(), fSigma.height());
-    ctx.ctm().mapVectors(&sigma, 1);
-    sigma.fX = SkMinScalar(sigma.fX, MAX_SIGMA);
-    sigma.fY = SkMinScalar(sigma.fY, MAX_SIGMA);
+    SkVector sigma = mapSigma(fSigma, ctx.ctm());
     offset->fX = rect.fLeft;
     offset->fY = rect.fTop;
     rect.offset(-srcOffset);