Bug 768775. For linear gradients where the gradient line is parallel to an axis and runs from one edge of a background tile to the other, we can repeat the background by just repeating the gradient instead of drawing individual tiles. r=jrmuizel

--HG--
extra : rebase_source : 81b9a7951ce78f60aa8eaeca4f66f62561133254

gfx/thebes/gfxContext.cpp

@@ -2099,4 +2099,4 @@ gfxContext::ChangeTransform(const Matrix &aNewMatrix)
   }
 
   mDT->SetTransform(aNewMatrix);
-}
+}

layout/base/nsCSSRendering.cpp

@@ -1997,6 +1997,7 @@ nsCSSRendering::PaintGradient(nsPresContext* aPresContext,
 
   // Create the gradient pattern.
   nsRefPtr<gfxPattern> gradientPattern;
+  bool forceRepeatToCoverTiles = false;
   if (aGradient->mShape == NS_STYLE_GRADIENT_SHAPE_LINEAR) {
     // Compute the actual gradient line ends we need to pass to cairo after
     // stops have been normalized.
@@ -2015,6 +2016,16 @@ nsCSSRendering::PaintGradient(nsPresContext* aPresContext,
 
     gradientPattern = new gfxPattern(gradientStart.x, gradientStart.y,
                                      gradientEnd.x, gradientEnd.y);
+
+    // When the gradient line is parallel to the x axis from the left edge
+    // to the right edge of a tile, then we can repeat by just repeating the
+    // gradient.
+    if ((gradientStart.y == gradientEnd.y && gradientStart.x == 0 &&
+         gradientEnd.x == oneCellArea.width) ||
+        (gradientStart.x == gradientEnd.x && gradientStart.y == 0 &&
+         gradientEnd.y == oneCellArea.height)) {
+      forceRepeatToCoverTiles = true;
+    }
   } else {
     NS_ASSERTION(firstStop >= 0.0,
                  "Negative stops not allowed for radial gradients");
@@ -2065,7 +2076,7 @@ nsCSSRendering::PaintGradient(nsPresContext* aPresContext,
   }
 
   // Set repeat mode. Default cairo extend mode is PAD.
-  if (aGradient->mRepeating) {
+  if (aGradient->mRepeating || forceRepeatToCoverTiles) {
     gradientPattern->SetExtend(gfxPattern::EXTEND_REPEAT);
   }
 
@@ -2084,8 +2095,9 @@ nsCSSRendering::PaintGradient(nsPresContext* aPresContext,
   // xStart/yStart are the top-left corner of the top-left tile.
   nscoord xStart = FindTileStart(dirty.x, aOneCellArea.x, aOneCellArea.width);
   nscoord yStart = FindTileStart(dirty.y, aOneCellArea.y, aOneCellArea.height);
-  nscoord xEnd = dirty.XMost();
-  nscoord yEnd = dirty.YMost();
+  nscoord xEnd = forceRepeatToCoverTiles ? xStart + aOneCellArea.width : dirty.XMost();
+  nscoord yEnd = forceRepeatToCoverTiles ? yStart + aOneCellArea.height : dirty.YMost();
+
   // x and y are the top-left corner of the tile to draw
   for (nscoord y = yStart; y < yEnd; y += aOneCellArea.height) {
     for (nscoord x = xStart; x < xEnd; x += aOneCellArea.width) {
@@ -2095,7 +2107,8 @@ nsCSSRendering::PaintGradient(nsPresContext* aPresContext,
                       appUnitsPerPixel);
       // The actual area to fill with this tile is the intersection of this
       // tile with the overall area we're supposed to be filling
-      gfxRect fillRect = tileRect.Intersect(areaToFill);
+      gfxRect fillRect =
+        forceRepeatToCoverTiles ? areaToFill : tileRect.Intersect(areaToFill);
       ctx->NewPath();
       ctx->Translate(tileRect.TopLeft());
       ctx->SetPattern(gradientPattern);