Bug 948265 - Support SourceAlpha keyword in SVG filter chains. r=mstange

gfx/src/FilterSupport.cpp

@@ -966,6 +966,11 @@ FilterNodeFromPrimitiveDescription(const FilterPrimitiveDescription& aDescriptio
       return transform;
     }
 
+    case PrimitiveType::ToAlpha:
+    {
+      return FilterWrappers::ToAlpha(aDT, aSources[0]);
+    }
+
     default:
       return nullptr;
   }
@@ -1001,6 +1006,7 @@ InputAlphaModelForPrimitive(const FilterPrimitiveDescription& aDescr,
   switch (aDescr.Type()) {
     case PrimitiveType::Tile:
     case PrimitiveType::Offset:
+    case PrimitiveType::ToAlpha:
       return aOriginalAlphaModel;
 
     case PrimitiveType::ColorMatrix:
@@ -1196,6 +1202,7 @@ ResultChangeRegionForPrimitive(const FilterPrimitiveDescription& aDescription,
 
     case PrimitiveType::ColorMatrix:
     case PrimitiveType::ComponentTransfer:
+    case PrimitiveType::ToAlpha:
       return aInputChangeRegions[0];
 
     case PrimitiveType::Morphology:
@@ -1425,6 +1432,7 @@ SourceNeededRegionForPrimitive(const FilterPrimitiveDescription& aDescription,
     case PrimitiveType::Merge:
     case PrimitiveType::ColorMatrix:
     case PrimitiveType::ComponentTransfer:
+    case PrimitiveType::ToAlpha:
       return aResultNeededRegion;
 
     case PrimitiveType::Morphology:

gfx/src/FilterSupport.h

@@ -270,6 +270,7 @@ MOZ_BEGIN_ENUM_CLASS(PrimitiveType)
   DropShadow,
   DiffuseLighting,
   SpecularLighting,
+  ToAlpha,
   Max
 MOZ_END_ENUM_CLASS(PrimitiveType)
 

layout/reftests/svg/filters/svg-filter-chains/reftest.list

@@ -9,5 +9,6 @@ default-preferences pref(layout.css.filters.enabled,true)
 == intersecting-filter-regions.svg intersecting-filter-regions-ref.svg
 == long-chain.svg simple-chain-ref.svg
 == multiple-primitives-per-filter.svg simple-chain-ref.svg
+== second-filter-uses-SourceAlpha.svg second-filter-uses-SourceAlpha.svg
 == second-filter-uses-SourceGraphic.svg simple-chain-ref.svg
 == simple-chain.svg simple-chain-ref.svg

layout/reftests/svg/filters/svg-filter-chains/second-filter-uses-SourceAlpha-ref.svg

@@ -0,0 +1,29 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<svg id="svg-root"
+  xmlns="http://www.w3.org/2000/svg"
+  xmlns:xlink="http://www.w3.org/1999/xlink">
+
+  <g id="testmeta">
+    <title>SVG Filter Chains: Second Filter Uses SourceAlpha</title>
+    <link rel="copyright"
+          href="http://www.w3.org/Graphics/SVG/Test/Copyright"/>
+    <link rel="license"
+          href="http://www.w3.org/Consortium/Legal/2008/03-bsd-license.html"/>
+    <link rel="author"
+          title="Max Vujovic"
+          href="mailto:mvujovic@adobe.com"/>
+    <link rel="help"
+          href="http://dev.w3.org/fxtf/filters/#FilterPrimitiveSubRegion"/>
+    <metadata class="flags">namespace svg</metadata>
+  </g>
+
+  <g id="test-body-content">
+    <filter id="blur">
+      <feGaussianBlur stdDeviation="3"/>
+    </filter>
+    <rect x="100" y="100" width="100" height="100" filter="url(#blur)" fill="#00ff00"/>
+  </g>
+</svg>

layout/reftests/svg/filters/svg-filter-chains/second-filter-uses-SourceAlpha.svg

@@ -0,0 +1,49 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<svg id="svg-root"
+  xmlns="http://www.w3.org/2000/svg"
+  xmlns:xlink="http://www.w3.org/1999/xlink">
+
+  <g id="testmeta">
+    <title>SVG Filter Chains: Second Filter Uses SourceAlpha</title>
+    <link rel="copyright"
+          href="http://www.w3.org/Graphics/SVG/Test/Copyright"/>
+    <link rel="license"
+          href="http://www.w3.org/Consortium/Legal/2008/03-bsd-license.html"/>
+    <link rel="author"
+          title="Max Vujovic"
+          href="mailto:mvujovic@adobe.com"/>
+    <link rel="help"
+          href="http://dev.w3.org/fxtf/filters/#FilterPrimitiveSubRegion"/>
+    <link rel="match"
+          href="second-filter-uses-SourceAlpha.svg" />
+    <metadata class="flags">namespace svg</metadata>
+    <desc class="assert">
+      In an SVG filter chain, this test verifies that a filter receives the
+      correct SourceAlpha input from the previous filter in the chain. If the
+      test passes, you should see a blurred green square.
+    </desc>
+  </g>
+
+  <g id="test-body-content">
+    <filter id="blur">
+      <feGaussianBlur stdDeviation="3"/>
+    </filter>
+    <filter id="add-green">
+      <!--
+        This filter receives transparent black and the alpha channel of the
+        previous blur filter. Then, it adds to the green channel where the alpha
+        channel is set, resulting in a blurred green square.
+      -->
+      <feComponentTransfer in="SourceAlpha">
+        <feFuncR type="identity"/>
+        <feFuncG type="table" tableValues="1 1"/>
+        <feFuncB type="identity"/>
+        <feFuncA type="identity"/>
+      </feComponentTransfer>
+    </filter>
+    <rect x="100" y="100" width="100" height="100" filter="url(#blur) url(#add-green)" fill="red"/>
+  </g>
+</svg>

layout/svg/nsSVGFilterInstance.cpp

@@ -34,6 +34,7 @@ nsSVGFilterInstance::nsSVGFilterInstance(const nsStyleFilter& aFilter,
   mTargetBBox(aTargetBBox),
   mUserSpaceToFilterSpaceScale(aUserSpaceToFilterSpaceScale),
   mFilterSpaceToUserSpaceScale(aFilterSpaceToUserSpaceScale),
+  mSourceAlphaAvailable(false),
   mInitialized(false) {
 
   // Get the filter frame.
@@ -288,9 +289,46 @@ GetLastResultIndex(const nsTArray<FilterPrimitiveDescription>& aPrimitiveDescrs)
     numPrimitiveDescrs - 1;
 }
 
+int32_t
+nsSVGFilterInstance::GetOrCreateSourceAlphaIndex(nsTArray<FilterPrimitiveDescription>& aPrimitiveDescrs)
+{
+  // If the SourceAlpha index has already been determined or created for this
+  // SVG filter, just return it.
+  if (mSourceAlphaAvailable)
+    return mSourceAlphaIndex;
+
+  // If this is the first filter in the chain, we can just use the
+  // kPrimitiveIndexSourceAlpha keyword to refer to the SourceAlpha of the
+  // original image.
+  if (mSourceGraphicIndex < 0) {
+    mSourceAlphaIndex = FilterPrimitiveDescription::kPrimitiveIndexSourceAlpha;
+    mSourceAlphaAvailable = true;
+    return mSourceAlphaIndex;
+  }
+
+  // Otherwise, create a primitive description to turn the previous filter's
+  // output into a SourceAlpha input.
+  FilterPrimitiveDescription descr(PrimitiveType::ToAlpha);
+  descr.SetInputPrimitive(0, mSourceGraphicIndex);
+
+  const FilterPrimitiveDescription& sourcePrimitiveDescr =
+    aPrimitiveDescrs[mSourceGraphicIndex];
+  descr.SetPrimitiveSubregion(sourcePrimitiveDescr.PrimitiveSubregion());
+  descr.SetIsTainted(sourcePrimitiveDescr.IsTainted());
+
+  ColorSpace colorSpace = sourcePrimitiveDescr.OutputColorSpace();
+  descr.SetInputColorSpace(0, colorSpace);
+  descr.SetOutputColorSpace(colorSpace);
+
+  aPrimitiveDescrs.AppendElement(descr);
+  mSourceAlphaIndex = aPrimitiveDescrs.Length() - 1;
+  mSourceAlphaAvailable = true;
+  return mSourceAlphaIndex;
+}
+
 nsresult
 nsSVGFilterInstance::GetSourceIndices(nsSVGFE* aPrimitiveElement,
-                                      const nsTArray<FilterPrimitiveDescription>& aPrimitiveDescrs,
+                                      nsTArray<FilterPrimitiveDescription>& aPrimitiveDescrs,
                                       const nsDataHashtable<nsStringHashKey, int32_t>& aImageTable,
                                       nsTArray<int32_t>& aSourceIndices)
 {
@@ -305,7 +343,7 @@ nsSVGFilterInstance::GetSourceIndices(nsSVGFE* aPrimitiveElement,
     if (str.EqualsLiteral("SourceGraphic")) {
       sourceIndex = mSourceGraphicIndex;
     } else if (str.EqualsLiteral("SourceAlpha")) {
-      sourceIndex = FilterPrimitiveDescription::kPrimitiveIndexSourceAlpha;
+      sourceIndex = GetOrCreateSourceAlphaIndex(aPrimitiveDescrs);
     } else if (str.EqualsLiteral("FillPaint")) {
       sourceIndex = FilterPrimitiveDescription::kPrimitiveIndexFillPaint;
     } else if (str.EqualsLiteral("StrokePaint")) {

layout/svg/nsSVGFilterInstance.h

@@ -173,6 +173,16 @@ private:
    */
   gfxMatrix GetUserSpaceToFrameSpaceInCSSPxTransform() const;
 
+  /**
+   * Appends a new FilterPrimitiveDescription to aPrimitiveDescrs that
+   * converts the FilterPrimitiveDescription at mSourceGraphicIndex into
+   * a SourceAlpha input for the next FilterPrimitiveDescription.
+   *
+   * The new FilterPrimitiveDescription zeros out the SourceGraphic's RGB
+   * channels and keeps the alpha channel intact.
+   */
+  int32_t GetOrCreateSourceAlphaIndex(nsTArray<FilterPrimitiveDescription>& aPrimitiveDescrs);
+
   /**
    * Finds the index in aPrimitiveDescrs of each input to aPrimitiveElement.
    * For example, if aPrimitiveElement is:
@@ -181,7 +191,7 @@ private:
    * FilterPrimitiveDescription representing "another-primitive".
    */
   nsresult GetSourceIndices(nsSVGFE* aPrimitiveElement,
-                            const nsTArray<FilterPrimitiveDescription>& aPrimitiveDescrs,
+                            nsTArray<FilterPrimitiveDescription>& aPrimitiveDescrs,
                             const nsDataHashtable<nsStringHashKey, int32_t>& aImageTable,
                             nsTArray<int32_t>& aSourceIndices);
 
@@ -240,6 +250,18 @@ private:
    */
   int32_t mSourceGraphicIndex;
 
+  /**
+   * The index of the FilterPrimitiveDescription that this SVG filter should use
+   * as its SourceAlpha, or the SourceAlpha keyword index if this is the first
+   * filter in a chain.
+   */
+  int32_t mSourceAlphaIndex;
+
+  /**
+   * SourceAlpha is available if GetOrCreateSourceAlphaIndex has been called.
+   */
+  int32_t mSourceAlphaAvailable;
+
   bool                    mInitialized;
 };