Patch by Mike Lawther (mikelawther@chromium.org).

The HTML5 canvas client of BlurDrawLooper needs the option to not apply the
canvas transform to the blur offset.

see
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-elemen...
- "The shadowOffsetX and shadowOffsetY attributes specify the distance that the
shadow will be offset in the positive horizontal and positive vertical distance
respectively. Their values are in coordinate space units. They are not affected
by the current transformation matrix."

This patch is part of fixing
http://code.google.com/p/chromium/issues/detail?id=64647.

Review URL:  http://codereview.appspot.com/3391041/



git-svn-id: http://skia.googlecode.com/svn/trunk@631 2bbb7eff-a529-9590-31e7-b0007b416f81

include/effects/SkBlurDrawLooper.h

@@ -29,7 +29,19 @@ class SkMaskFilter;
 */
 class SkBlurDrawLooper : public SkDrawLooper {
 public:
-    SkBlurDrawLooper(SkScalar radius, SkScalar dx, SkScalar dy, SkColor color);
+    enum BlurFlags {
+        kNone_BlurFlag = 0x00,
+        /** 
+            The blur layer's dx/dy/radius aren't affected by the canvas 
+            transform.
+        */
+        kIgnoreTransform_BlurFlag = 0x01,
+        /** mask for all blur flags */
+        kAll_BlurFlag = 0x01
+    };
+
+    SkBlurDrawLooper(SkScalar radius, SkScalar dx, SkScalar dy, SkColor color, 
+                     uint32_t flags = kNone_BlurFlag);
     virtual ~SkBlurDrawLooper();
 
     // overrides from SkDrawLooper
@@ -41,6 +53,7 @@ public:
         return SkNEW_ARGS(SkBlurDrawLooper, (buffer));
     }
 
+
 protected:
     SkBlurDrawLooper(SkFlattenableReadBuffer&);
     // overrides from SkFlattenable
@@ -55,6 +68,7 @@ private:
     SkColor         fBlurColor;
     SkColor         fSavedColor;    // remember the original
     int             fSaveCount;
+    uint32_t        fBlurFlags;  
 
     enum State {
         kBeforeEdge,

include/effects/SkBlurMaskFilter.h

@@ -32,12 +32,22 @@ public:
         kBlurStyleCount
     };
 
+    enum BlurFlags {
+        kNone_BlurFlag = 0x00,
+        /** The blur layer's radius is not affected by transforms */
+        kIgnoreTransform_BlurFlag = 0x01,
+        /** mask for all blur flags */
+        kAll_BlurFlag = 0x01
+    };
+
     /** Create a blur maskfilter.
         @param radius   The radius to extend the blur from the original mask. Must be > 0.
         @param style    The BlurStyle to use
+        @param flags    Flags to use - defaults to none
         @return The new blur maskfilter
     */
-    static SkMaskFilter* Create(SkScalar radius, BlurStyle style);
+    static SkMaskFilter* Create(SkScalar radius, BlurStyle style, 
+                                uint32_t flags = kNone_BlurFlag);
 
     /** Create an emboss maskfilter
         @param direction    array of 3 scalars [x, y, z] specifying the direction of the light source

src/effects/SkBlurDrawLooper.cpp

@@ -5,12 +5,20 @@
 #include "SkMaskFilter.h"
 
 SkBlurDrawLooper::SkBlurDrawLooper(SkScalar radius, SkScalar dx, SkScalar dy,
-                                   SkColor color)
-    : fDx(dx), fDy(dy), fBlurColor(color)
+                                   SkColor color, uint32_t flags)
+    : fDx(dx), fDy(dy), fBlurColor(color), fBlurFlags(flags)
 {
+    SkASSERT(flags <= kAll_BlurFlag);
     if (radius > 0)
+    {
+        uint32_t blurFlags = flags & kIgnoreTransform_BlurFlag ? 
+            SkBlurMaskFilter::kIgnoreTransform_BlurFlag : 
+            SkBlurMaskFilter::kNone_BlurFlag;
+
         fBlur = SkBlurMaskFilter::Create(radius,
-                                         SkBlurMaskFilter::kNormal_BlurStyle);
+                                         SkBlurMaskFilter::kNormal_BlurStyle, 
+                                         blurFlags);
+    }
     else
         fBlur = NULL;
 }
@@ -21,6 +29,7 @@ SkBlurDrawLooper::SkBlurDrawLooper(SkFlattenableReadBuffer& buffer)
     fDy = buffer.readScalar();
     fBlurColor = buffer.readU32();
     fBlur = static_cast<SkMaskFilter*>(buffer.readFlattenable());
+    fBlurFlags = buffer.readU32() & kAll_BlurFlag;
 }
 
 SkBlurDrawLooper::~SkBlurDrawLooper()
@@ -34,6 +43,7 @@ void SkBlurDrawLooper::flatten(SkFlattenableWriteBuffer& buffer)
     buffer.writeScalar(fDy);
     buffer.write32(fBlurColor);
     buffer.writeFlattenable(fBlur);
+    buffer.write32(fBlurFlags);
 }
 
 void SkBlurDrawLooper::init(SkCanvas* canvas, SkPaint* paint)
@@ -58,7 +68,16 @@ bool SkBlurDrawLooper::next()
         fPaint->setColor(fBlurColor);
         fPaint->setMaskFilter(fBlur);
         fCanvas->save(SkCanvas::kMatrix_SaveFlag);
+        if (fBlurFlags & kIgnoreTransform_BlurFlag)
+        {
+            SkMatrix transform(fCanvas->getTotalMatrix());
+            transform.postTranslate(fDx, fDy);
+            fCanvas->setMatrix(transform);
+        }
+        else
+        {
             fCanvas->translate(fDx, fDy);
+        }
         fState = kAfterEdge;
         return true;
     case kAfterEdge:

src/effects/SkBlurMaskFilter.cpp

@@ -22,7 +22,7 @@
 
 class SkBlurMaskFilterImpl : public SkMaskFilter {
 public:
-    SkBlurMaskFilterImpl(SkScalar radius, SkBlurMaskFilter::BlurStyle style);
+    SkBlurMaskFilterImpl(SkScalar radius, SkBlurMaskFilter::BlurStyle style, uint32_t flags);
 
     // overrides from SkMaskFilter
     virtual SkMask::Format getFormat();
@@ -39,24 +39,28 @@ public:
 private:
     SkScalar                    fRadius;
     SkBlurMaskFilter::BlurStyle fBlurStyle;
+    uint32_t                    fBlurFlags;
 
     SkBlurMaskFilterImpl(SkFlattenableReadBuffer&);
     
     typedef SkMaskFilter INHERITED;
 };
 
-SkMaskFilter* SkBlurMaskFilter::Create(SkScalar radius, SkBlurMaskFilter::BlurStyle style)
+SkMaskFilter* SkBlurMaskFilter::Create(SkScalar radius, SkBlurMaskFilter::BlurStyle style,
+                                       uint32_t flags)
 {
-    if (radius <= 0 || (unsigned)style >= SkBlurMaskFilter::kBlurStyleCount)
+    if (radius <= 0 || (unsigned)style >= SkBlurMaskFilter::kBlurStyleCount 
+        || flags > SkBlurMaskFilter::kAll_BlurFlag)
         return NULL;
 
-    return SkNEW_ARGS(SkBlurMaskFilterImpl, (radius, style));
+    return SkNEW_ARGS(SkBlurMaskFilterImpl, (radius, style, flags));
 }
 
 /////////////////////////////////////////////////////////////////////////////////////////////////////////
 
-SkBlurMaskFilterImpl::SkBlurMaskFilterImpl(SkScalar radius, SkBlurMaskFilter::BlurStyle style)
-    : fRadius(radius), fBlurStyle(style)
+SkBlurMaskFilterImpl::SkBlurMaskFilterImpl(SkScalar radius, SkBlurMaskFilter::BlurStyle style,
+                                           uint32_t flags)
+    : fRadius(radius), fBlurStyle(style), fBlurFlags(flags)
 {
 #if 0
     fGamma = NULL;
@@ -71,6 +75,7 @@ SkBlurMaskFilterImpl::SkBlurMaskFilterImpl(SkScalar radius, SkBlurMaskFilter::Bl
 #endif
     SkASSERT(radius >= 0);
     SkASSERT((unsigned)style < SkBlurMaskFilter::kBlurStyleCount);
+    SkASSERT(flags <= SkBlurMaskFilter::kAll_BlurFlag);
 }
 
 SkMask::Format SkBlurMaskFilterImpl::getFormat()
@@ -80,7 +85,12 @@ SkMask::Format SkBlurMaskFilterImpl::getFormat()
 
 bool SkBlurMaskFilterImpl::filterMask(SkMask* dst, const SkMask& src, const SkMatrix& matrix, SkIPoint* margin)
 {
-    SkScalar radius = matrix.mapRadius(fRadius);
+    SkScalar radius;
+    if (fBlurFlags & SkBlurMaskFilter::kIgnoreTransform_BlurFlag)
+        radius = fRadius;
+    else
+        radius = matrix.mapRadius(fRadius);
+
     // To avoid unseemly allocation requests (esp. for finite platforms like
     // handset) we limit the radius so something manageable. (as opposed to
     // a request like 10,000)
@@ -113,6 +123,7 @@ SkBlurMaskFilterImpl::SkBlurMaskFilterImpl(SkFlattenableReadBuffer& buffer) : Sk
 {
     fRadius = buffer.readScalar();
     fBlurStyle = (SkBlurMaskFilter::BlurStyle)buffer.readS32();
+    fBlurFlags = buffer.readU32() & SkBlurMaskFilter::kAll_BlurFlag;
     SkASSERT(fRadius >= 0);
     SkASSERT((unsigned)fBlurStyle < SkBlurMaskFilter::kBlurStyleCount);
 }
@@ -122,6 +133,7 @@ void SkBlurMaskFilterImpl::flatten(SkFlattenableWriteBuffer& buffer)
     this->INHERITED::flatten(buffer);
     buffer.writeScalar(fRadius);
     buffer.write32(fBlurStyle);
+    buffer.write32(fBlurFlags);
 }
 
 ///////////////////////////////////////////////////////////////////////////////