Bug 1365876. Blur text shadows on the CPU. r=lsalzman

gfx/thebes/gfxBlur.cpp

@@ -36,14 +36,16 @@ gfxAlphaBoxBlur::Init(gfxContext* aDestinationCtx,
                       const IntSize& aSpreadRadius,
                       const IntSize& aBlurRadius,
                       const gfxRect* aDirtyRect,
-                      const gfxRect* aSkipRect)
+                      const gfxRect* aSkipRect,
+                      bool aUseHardwareAccel)
 {
   DrawTarget* refDT = aDestinationCtx->GetDrawTarget();
   Maybe<Rect> dirtyRect = aDirtyRect ? Some(ToRect(*aDirtyRect)) : Nothing();
   Maybe<Rect> skipRect = aSkipRect ? Some(ToRect(*aSkipRect)) : Nothing();
   RefPtr<DrawTarget> dt =
     InitDrawTarget(refDT, ToRect(aRect), aSpreadRadius, aBlurRadius,
-                   dirtyRect.ptrOr(nullptr), skipRect.ptrOr(nullptr));
+                   dirtyRect.ptrOr(nullptr), skipRect.ptrOr(nullptr),
+                   aUseHardwareAccel);
   if (!dt) {
     return nullptr;
   }
@@ -60,7 +62,8 @@ gfxAlphaBoxBlur::InitDrawTarget(const DrawTarget* aReferenceDT,
                                 const IntSize& aSpreadRadius,
                                 const IntSize& aBlurRadius,
                                 const Rect* aDirtyRect,
-                                const Rect* aSkipRect)
+                                const Rect* aSkipRect,
+                                bool aUseHardwareAccel)
 {
   mBlur.Init(aRect, aSpreadRadius, aBlurRadius, aDirtyRect, aSkipRect);
   size_t blurDataSize = mBlur.GetSurfaceAllocationSize();
@@ -75,10 +78,10 @@ gfxAlphaBoxBlur::InitDrawTarget(const DrawTarget* aReferenceDT,
   // Otherwise, DrawSurfaceWithShadow only supports square blurs without spread.
   // When blurring small draw targets such as short spans text, the cost of
   // creating and flushing an accelerated draw target may exceed the speedup
-  // gained from the faster blur, so we also make sure the blurred data exceeds
-  // a sufficient number of pixels to offset this cost.
+  // gained from the faster blur. It's up to the users of this blur
+  // to determine whether they want to use hardware acceleration.
   if (aBlurRadius.IsSquare() && aSpreadRadius.IsEmpty() &&
-      blurDataSize >= 8192 &&
+      aUseHardwareAccel &&
       backend == BackendType::DIRECT2D1_1) {
     mAccelerated = true;
     mDrawTarget =

gfx/thebes/gfxBlur.h

@@ -74,6 +74,9 @@ public:
      * @param aSkipRect A pointer to a rect, measured in device units, that
      *  represents an area where blurring is unnecessary and shouldn't be done
      *  for speed reasons. It is safe to pass nullptr here.
+     *
+     * @param aUseHardwareAccel Flag to state whether or not we can use hardware
+     *  acceleration to speed up this blur.
      */
     already_AddRefed<gfxContext>
     Init(gfxContext* aDestinationCtx,
@@ -81,7 +84,8 @@ public:
          const mozilla::gfx::IntSize& aSpreadRadius,
          const mozilla::gfx::IntSize& aBlurRadius,
          const gfxRect* aDirtyRect,
-         const gfxRect* aSkipRect);
+         const gfxRect* aSkipRect,
+         bool aUseHardwareAccel = true);
 
     already_AddRefed<DrawTarget>
     InitDrawTarget(const mozilla::gfx::DrawTarget* aReferenceDT,
@@ -89,7 +93,8 @@ public:
                    const mozilla::gfx::IntSize& aSpreadRadius,
                    const mozilla::gfx::IntSize& aBlurRadius,
                    const mozilla::gfx::Rect* aDirtyRect = nullptr,
-                   const mozilla::gfx::Rect* aSkipRect = nullptr);
+                   const mozilla::gfx::Rect* aSkipRect = nullptr,
+                   bool aUseHardwareAccel = true);
 
     /**
      * Performs the blur and optionally colors the result if aShadowColor is not null.

layout/base/nsLayoutUtils.cpp

@@ -6025,7 +6025,8 @@ nsLayoutUtils::PaintTextShadow(const nsIFrame* aFrame,
     nsContextBoxBlur contextBoxBlur;
     gfxContext* shadowContext = contextBoxBlur.Init(shadowRect, 0, blurRadius,
                                                     presCtx->AppUnitsPerDevPixel(),
-                                                    aDestCtx, aDirtyRect, nullptr);
+                                                    aDestCtx, aDirtyRect, nullptr,
+                                                    nsContextBoxBlur::DISABLE_HARDWARE_ACCELERATION_BLUR);
     if (!shadowContext)
       continue;
 

layout/generic/nsTextFrame.cpp

@@ -6972,12 +6972,14 @@ nsTextFrame::PaintShadows(nsCSSShadowArray* aShadow,
 
   // If the textrun uses any color or SVG fonts, we need to force use of a mask
   // for shadow rendering even if blur radius is zero.
-  uint32_t blurFlags = 0;
+  // Force disable hardware acceleration for text shadows since it's usually
+  // more expensive than just doing it on the CPU.
+  uint32_t blurFlags = nsContextBoxBlur::DISABLE_HARDWARE_ACCELERATION_BLUR;
   uint32_t numGlyphRuns;
   const gfxTextRun::GlyphRun* run = mTextRun->GetGlyphRuns(&numGlyphRuns);
   while (numGlyphRuns-- > 0) {
     if (run->mFont->AlwaysNeedsMaskForShadow()) {
-      blurFlags = nsContextBoxBlur::FORCE_MASK;
+      blurFlags |= nsContextBoxBlur::FORCE_MASK;
       break;
     }
     run++;

layout/painting/nsCSSRendering.cpp

@@ -4292,13 +4292,16 @@ nsContextBoxBlur::Init(const nsRect& aRect, nscoord aSpreadRadius,
 
   // Create the temporary surface for blurring
   dirtyRect = transform.TransformBounds(dirtyRect);
+  bool useHardwareAccel = !(aFlags & DISABLE_HARDWARE_ACCELERATION_BLUR);
   if (aSkipRect) {
     gfxRect skipRect = transform.TransformBounds(*aSkipRect);
     mContext = mAlphaBoxBlur.Init(aDestinationCtx, rect, spreadRadius,
-                                  blurRadius, &dirtyRect, &skipRect);
+                                  blurRadius, &dirtyRect, &skipRect,
+                                  useHardwareAccel);
   } else {
     mContext = mAlphaBoxBlur.Init(aDestinationCtx, rect, spreadRadius,
-                                  blurRadius, &dirtyRect, nullptr);
+                                  blurRadius, &dirtyRect, nullptr,
+                                  useHardwareAccel);
   }
 
   if (mContext) {

layout/painting/nsCSSRendering.h

@@ -715,7 +715,8 @@ class nsContextBoxBlur {
 
 public:
   enum {
-    FORCE_MASK = 0x01
+    FORCE_MASK = 0x01,
+    DISABLE_HARDWARE_ACCELERATION_BLUR = 0x02
   };
   /**
    * Prepares a gfxContext to draw on. Do not call this twice; if you want