Bug 458031. Take dirty rect into account to limit box-shadow computation. r+sr=roc

layout/base/nsCSSRendering.cpp

@@ -1054,7 +1054,8 @@ void
 nsCSSRendering::PaintBoxShadow(nsPresContext* aPresContext,
                                nsIRenderingContext& aRenderingContext,
                                nsIFrame* aForFrame,
-                               const nsPoint& aForFramePt)
+                               const nsPoint& aForFramePt,
+                               const nsRect& aDirtyRect)
 {
   nsMargin      borderValues;
   PRIntn        sidesToSkip;
@@ -1076,6 +1077,8 @@ nsCSSRendering::PaintBoxShadow(nsPresContext* aPresContext,
                     twipsPerPixel, &borderRadii);
 
   gfxRect frameGfxRect = RectToGfxRect(frameRect, twipsPerPixel);
+  gfxRect dirtyGfxRect = RectToGfxRect(aDirtyRect, twipsPerPixel);
+
   for (PRUint32 i = styleBorder->mBoxShadow->Length(); i > 0; --i) {
     nsCSSShadowItem* shadowItem = styleBorder->mBoxShadow->ShadowAt(i - 1);
     gfxRect shadowRect(frameRect.x, frameRect.y, frameRect.width, frameRect.height);
@@ -1097,9 +1100,9 @@ nsCSSRendering::PaintBoxShadow(nsPresContext* aPresContext,
     nsRefPtr<gfxContext> shadowContext;
     nsContextBoxBlur blurringArea;
 
-    // shadowRect has already been converted to device pixels, pass 1 as the appunits/pixel value
+    // shadowRect is already in device pixels, pass 1 as the appunits/pixel value
     blurRadius /= twipsPerPixel;
-    shadowContext = blurringArea.Init(shadowRect, blurRadius, 1, renderContext);
+    shadowContext = blurringArea.Init(shadowRect, blurRadius, 1, renderContext, dirtyGfxRect);
     if (!shadowContext)
       continue;
 
@@ -2540,7 +2543,8 @@ GetTextDecorationRectInternal(const gfxPoint& aPt,
 gfxContext*
 nsContextBoxBlur::Init(const gfxRect& aRect, nscoord aBlurRadius,
                        PRInt32 aAppUnitsPerDevPixel,
-                       gfxContext* aDestinationCtx)
+                       gfxContext* aDestinationCtx,
+                       const gfxRect& aDirtyRect)
 {
   mDestinationCtx = aDestinationCtx;
 
@@ -2561,9 +2565,24 @@ nsContextBoxBlur::Init(const gfxRect& aRect, nscoord aBlurRadius,
     return mContext;
   }
 
+  gfxRect dirtyRect = aDirtyRect;
+  dirtyRect.ScaleInverse(aAppUnitsPerDevPixel);
+  gfxRect rectWithBlur = rect;
+  rectWithBlur.Outset(blurRadius);
+
+  // Determine the area of the shadow we need.
+  mRequiredShadowArea = dirtyRect.Intersect(rectWithBlur);
+
   mDestinationCtx = aDestinationCtx;
 
-  mContext = blur.Init(rect, gfxIntSize(blurRadius, blurRadius));
+ // XXX the temporary surface will be the mRequiredShadowArea inflated by
+ // blurRadius in each direction so that the required shadow pixels are computed
+ // correctly. We could actually use a smaller temporary surface by observing
+ // that where the temporary surface is outside the rectWithBlur, the pixel
+ // values are guaranteed to be fully transparent, so we could intersect the
+ // inflated mRequiredShadowArea with rectWithBlur to compute the temporary
+ // surface area. But we're not doing that right now because it's more complex to do.
+  mContext = blur.Init(mRequiredShadowArea, gfxIntSize(blurRadius, blurRadius));
   return mContext;
 }
 
@@ -2573,7 +2592,12 @@ nsContextBoxBlur::DoPaint()
   if (mContext == mDestinationCtx)
     return;
 
+  mDestinationCtx->Save();
+  mDestinationCtx->NewPath();
+  mDestinationCtx->Rectangle(mRequiredShadowArea);
+  mDestinationCtx->Clip();
   blur.Paint(mDestinationCtx);
+  mDestinationCtx->Restore();
 }
 
 gfxContext*
@@ -2581,3 +2605,4 @@ nsContextBoxBlur::GetContext()
 {
   return mContext;
 }
+

layout/base/nsCSSRendering.h

@@ -64,7 +64,8 @@ struct nsCSSRendering {
   static void PaintBoxShadow(nsPresContext* aPresContext,
                              nsIRenderingContext& aRenderingContext,
                              nsIFrame* aForFrame,
-                             const nsPoint& aForFramePt);
+                             const nsPoint& aForFramePt,
+                             const nsRect& aDirtyRect);
 
   /**
    * Render the border for an element using css rendering rules
@@ -288,6 +289,9 @@ public:
    *                             set the color on this context before
    *                             calling Init().
    *
+   * @param aDirtyRect           The absolute dirty rect in app units. Used to
+   *                             optimize the temporary surface size and speed up blur.
+   *
    * @return            A blank 8-bit alpha-channel-only graphics context to
    *                    draw on, or null on error. Must not be freed. The
    *                    context has a device offset applied to it given by
@@ -302,7 +306,8 @@ public:
    * directly on it instead of any temporary surface created in this class.
    */
   gfxContext* Init(const gfxRect& aRect, nscoord aBlurRadius,
-                   PRInt32 aAppUnitsPerDevPixel, gfxContext* aDestinationCtx);
+                   PRInt32 aAppUnitsPerDevPixel, gfxContext* aDestinationCtx,
+                   const gfxRect& aDirtyRect);
 
   /**
    * Does the actual blurring and mask applying. Users of this object *must*
@@ -323,6 +328,8 @@ protected:
   nsRefPtr<gfxContext> mContext;
   gfxContext* mDestinationCtx;
 
+  gfxRect mRequiredShadowArea;
+  
 };
 
 #endif /* nsCSSRendering_h___ */

layout/base/nsDisplayList.cpp

@@ -651,7 +651,7 @@ nsDisplayBoxShadow::Paint(nsDisplayListBuilder* aBuilder,
      nsIRenderingContext* aCtx, const nsRect& aDirtyRect) {
   nsPoint offset = aBuilder->ToReferenceFrame(mFrame);
   nsCSSRendering::PaintBoxShadow(mFrame->PresContext(), *aCtx,
-                                 mFrame, offset);
+                                 mFrame, offset, aDirtyRect);
 }
 
 nsRect

layout/generic/nsHTMLContainerFrame.cpp

@@ -202,10 +202,12 @@ nsDisplayTextShadow::Paint(nsDisplayListBuilder* aBuilder,
   gfxRect shadowRect = gfxRect(pt.x, pt.y, innerWidthInAppUnits, mFrame->GetSize().height);
   gfxContext* thebesCtx = aCtx->ThebesContext();
 
+  gfxRect dirtyRect(aDirtyRect.x, aDirtyRect.y, aDirtyRect.width, aDirtyRect.height);
+
   nsContextBoxBlur contextBoxBlur;
   gfxContext* shadowCtx = contextBoxBlur.Init(shadowRect, mBlurRadius,
                                               mFrame->PresContext()->AppUnitsPerDevPixel(),
-                                              thebesCtx);
+                                              thebesCtx, dirtyRect);
   if (!shadowCtx)
     return;
 

layout/generic/nsTextFrameThebes.cpp

@@ -4150,7 +4150,7 @@ nsTextFrame::PaintOneShadow(PRUint32 aOffset, PRUint32 aLength,
   nsContextBoxBlur contextBoxBlur;
   gfxContext* shadowContext = contextBoxBlur.Init(shadowRect, blurRadius,
                                                   PresContext()->AppUnitsPerDevPixel(),
-                                                  aCtx);
+                                                  aCtx, aDirtyRect);
   if (!shadowContext)
     return;
 

layout/xul/base/src/nsTextBoxFrame.cpp

@@ -387,7 +387,8 @@ nsTextBoxFrame::PaintTitle(nsIRenderingContext& aRenderingContext,
         PaintOneShadow(aRenderingContext.ThebesContext(),
                        textRect,
                        textStyle->mTextShadow->ShadowAt(i - 1),
-                       GetStyleColor()->mColor);
+                       GetStyleColor()->mColor,
+                       aDirtyRect);
       }
     }
 
@@ -563,7 +564,8 @@ nsTextBoxFrame::DrawText(nsIRenderingContext& aRenderingContext,
 void nsTextBoxFrame::PaintOneShadow(gfxContext*      aCtx,
                                     const nsRect&    aTextRect,
                                     nsCSSShadowItem* aShadowDetails,
-                                    const nscolor&   aForegroundColor) {
+                                    const nscolor&   aForegroundColor,
+                                    const nsRect&    aDirtyRect) {
   nsPoint shadowOffset(aShadowDetails->mXOffset,
                        aShadowDetails->mYOffset);
   nscoord blurRadius = PR_MAX(aShadowDetails->mRadius, 0);
@@ -572,11 +574,12 @@ void nsTextBoxFrame::PaintOneShadow(gfxContext*      aCtx,
   shadowRect.MoveBy(shadowOffset);
 
   gfxRect shadowRectGFX(shadowRect.x, shadowRect.y, shadowRect.width, shadowRect.height);
+  gfxRect dirtyRectGFX(aDirtyRect.x, aDirtyRect.y, aDirtyRect.width, aDirtyRect.height);
 
   nsContextBoxBlur contextBoxBlur;
   gfxContext* shadowContext = contextBoxBlur.Init(shadowRectGFX, blurRadius,
                                                   PresContext()->AppUnitsPerDevPixel(),
-                                                  aCtx);
+                                                  aCtx, dirtyRectGFX);
 
   if (!shadowContext)
     return;

layout/xul/base/src/nsTextBoxFrame.h

@@ -134,7 +134,8 @@ private:
   void PaintOneShadow(gfxContext *     aCtx,
                       const nsRect&    aTextRect,
                       nsCSSShadowItem* aShadowDetails,
-                      const nscolor&   aForegroundColor);
+                      const nscolor&   aForegroundColor,
+                      const nsRect&    aDirtyRect);
 
 
   CroppingStyle mCropType;