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Bug 787947. Avoid scaling by 0 when snapping gradient tiles. r=jrmuizel

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This commit is contained in:
Robert O'Callahan
2012-09-25 15:25:48 +12:00
parent 8e9785466d
commit b4af1d44d6
4 changed files with 32 additions and 19 deletions
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42
layout/base/nsCSSRendering.cpp
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@@ -2290,6 +2290,7 @@ nsCSSRendering::PaintGradient(nsPresContext* aPresContext,
gfxRect areaToFill =
nsLayoutUtils::RectToGfxRect(aFillArea, appUnitsPerPixel);
gfxMatrix ctm = ctx->CurrentMatrix();
bool isCTMPreservingAxisAlignedRectangles = ctm.PreservesAxisAlignedRectangles();
// xStart/yStart are the top-left corner of the top-left tile.
nscoord xStart = FindTileStart(dirty.x, aOneCellArea.x, aOneCellArea.width);
@@ -2309,27 +2310,30 @@ nsCSSRendering::PaintGradient(nsPresContext* aPresContext,
gfxRect fillRect =
pattern->mCoversTile ? areaToFill : tileRect.Intersect(areaToFill);
ctx->NewPath();
// If we can snap the gradient tile and fill rects, do so, but make sure
// that the gradient is scaled precisely to the tile rect.
gfxRect fillRectSnapped = fillRect;
// Don't snap the tileRect directly since that would lose information
// about the orientation of the current transform (i.e. vertical or
// horizontal flipping). Instead snap the corners independently so if
// the CTM has a flip, our Scale() below preserves the flip.
gfxPoint tileRectSnappedTopLeft = tileRect.TopLeft();
gfxPoint tileRectSnappedBottomRight = tileRect.BottomRight();
if (ctx->UserToDevicePixelSnapped(fillRectSnapped, true) &&
ctx->UserToDevicePixelSnapped(tileRectSnappedTopLeft, true) &&
ctx->UserToDevicePixelSnapped(tileRectSnappedBottomRight, true)) {
// Try snapping the fill rect. Snap its top-left and bottom-right
// independently to preserve the orientation.
gfxPoint snappedFillRectTopLeft = fillRect.TopLeft();
gfxPoint snappedFillRectBottomRight = fillRect.BottomRight();
if (isCTMPreservingAxisAlignedRectangles &&
ctx->UserToDevicePixelSnapped(snappedFillRectTopLeft, true) &&
ctx->UserToDevicePixelSnapped(snappedFillRectBottomRight, true)) {
if (snappedFillRectTopLeft.x == snappedFillRectBottomRight.x ||
snappedFillRectTopLeft.y == snappedFillRectBottomRight.y) {
// Nothing to draw; avoid scaling by zero and other weirdness that
// could put the context in an error state.
continue;
}
// Set the context's transform to the transform that maps fillRect to
// snappedFillRect. The part of the gradient that was going to
// exactly fill fillRect will fill snappedFillRect instead.
ctx->IdentityMatrix();
ctx->Rectangle(fillRectSnapped);
ctx->Translate(tileRectSnappedTopLeft);
ctx->Scale((tileRectSnappedBottomRight.x - tileRectSnappedTopLeft.x)/tileRect.width,
(tileRectSnappedBottomRight.y - tileRectSnappedTopLeft.y)/tileRect.height);
} else {
ctx->Rectangle(fillRect);
ctx->Translate(tileRect.TopLeft());
ctx->Translate(snappedFillRectTopLeft);
ctx->Scale((snappedFillRectBottomRight.x - snappedFillRectTopLeft.x)/fillRect.width,
(snappedFillRectBottomRight.y - snappedFillRectTopLeft.y)/fillRect.height);
ctx->Translate(-fillRect.TopLeft());
}
ctx->Rectangle(fillRect);
ctx->Translate(tileRect.TopLeft());
ctx->SetPattern(pattern->mPattern);
ctx->Fill();
ctx->SetMatrix(ctm);