Bug 455279. Fix mask alpha computation so that it works when the incoming gfxContext has a non-identity transform. r=longsonr,sr=mats

layout/reftests/svg/mask-transformed-01-ref.svg

@@ -0,0 +1,8 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/licenses/publicdomain/
+-->
+<svg xmlns="http://www.w3.org/2000/svg" width="400" height="400">
+  <rect width="50%" height="50%" fill="lime"/>
+</svg>
+

layout/reftests/svg/mask-transformed-01.svg

@@ -0,0 +1,17 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/licenses/publicdomain/
+-->
+<svg xmlns="http://www.w3.org/2000/svg" width="400" height="400">
+  <defs>
+    <mask id="m1" maskUnits="objectBoundingBox" maskContentUnits="objectBoundingBox">
+      <rect x="0" y="0" width="1" height="1" fill="white"/>
+    </mask>
+  </defs>
+  <foreignObject width="100%" height="100%" transform="scale(0.5)">
+    <svg style="width:100%; height:100%;">
+      <rect width="100%" height="100%" fill="lime" mask="url(#m1)"/>
+    </svg>
+  </foreignObject>
+</svg>
+

layout/reftests/svg/reftest.list

@@ -52,6 +52,7 @@ fails == inline-in-xul-basic-01.xul pass.svg
 == invalid-text-01.svg pass.svg
 == linearGradient-basic-01.svg pass.svg
 == linearGradient-basic-02.svg pass.svg
+== mask-transformed-01.svg mask-transformed-01-ref.svg
 == nested-viewBox-01.svg pass.svg
 == objectBoundingBox-and-pattern-01a.svg objectBoundingBox-and-pattern-01-ref.svg
 == objectBoundingBox-and-pattern-01b.svg objectBoundingBox-and-pattern-01-ref.svg

layout/svg/base/src/nsSVGMaskFrame.cpp

@@ -106,20 +106,13 @@ nsSVGMaskFrame::ComputeMaskAlpha(nsSVGRenderState *aContext,
     nsSVGUtils::PaintChildWithEffects(aContext, nsnull, kid);
   }
 
+  gfxRect clipExtents = gfx->GetClipExtents();
   gfx->Restore();
 
   nsRefPtr<gfxPattern> pattern = gfx->PopGroup();
   if (!pattern || pattern->CairoStatus())
     return nsnull;
 
-  nsRefPtr<gfxASurface> surface = pattern->GetSurface();
-  if (!surface || surface->CairoStatus())
-    return nsnull;
-
-  surface->SetDeviceOffset(gfxPoint(0,0));
-
-  gfxRect clipExtents = gfx->GetClipExtents();
-
 #ifdef DEBUG_tor
   fprintf(stderr, "clip extent: %f,%f %fx%f\n",
           clipExtents.X(), clipExtents.Y(),
@@ -143,10 +136,11 @@ nsSVGMaskFrame::ComputeMaskAlpha(nsSVGRenderState *aContext,
     new gfxImageSurface(surfaceSize, gfxASurface::ImageFormatARGB32);
   if (!image || image->CairoStatus())
     return nsnull;
+  image->SetDeviceOffset(-clipExtents.pos);
 
   gfxContext transferCtx(image);
   transferCtx.SetOperator(gfxContext::OPERATOR_SOURCE);
-  transferCtx.SetSource(surface);
+  transferCtx.SetPattern(pattern);
   transferCtx.Paint();
 
   PRUint8 *data   = image->Data();
@@ -172,10 +166,7 @@ nsSVGMaskFrame::ComputeMaskAlpha(nsSVGRenderState *aContext,
     }
 
   gfxPattern *retval = new gfxPattern(image);
-  if (retval) {
+  NS_IF_ADDREF(retval);
-    retval->SetMatrix(gfxMatrix().Translate(-clipExtents.pos));
-    NS_ADDREF(retval);
-  }
   return retval;
 }