/* static */ void
gfxAlphaBoxBlur::BlurRectangle(gfxContext* aDestinationCtx,
const gfxRect& aRect,
RectCornerRadii* aCornerRadii,
const gfxPoint& aBlurStdDev,
const gfxRGBA& aShadowColor,
const gfxRect& aDirtyRect,
const gfxRect& aSkipRect)
{
DrawTarget& destDrawTarget = *aDestinationCtx->GetDrawTarget();
IntSize blurRadius = CalculateBlurRadius(aBlurStdDev);
IntRect rect = RoundedToInt(ToRect(aRect));
IntMargin extendDestBy;
IntMargin slice;
RefPtr<SourceSurface> boxShadow = GetBlur(destDrawTarget,
rect.Size(), blurRadius,
aCornerRadii, aShadowColor,
extendDestBy, slice);
if (!boxShadow) {
return;
}
destDrawTarget.PushClipRect(ToRect(aDirtyRect));
// Copy the right parts from boxShadow into destDrawTarget. The middle parts
// will be stretched, border-image style.
Rect srcOuter(Point(), Size(boxShadow->GetSize()));
Rect srcInner = srcOuter;
srcInner.Deflate(Margin(slice));
rect.Inflate(extendDestBy);
Rect dstOuter(rect);
Rect dstInner(rect);
dstInner.Deflate(Margin(slice));
Rect skipRect = ToRect(aSkipRect);
if (srcInner.IsEqualInterior(srcOuter)) {
MOZ_ASSERT(dstInner.IsEqualInterior(dstOuter));
// The target rect is smaller than the minimal size so just draw the surface
destDrawTarget.DrawSurface(boxShadow, dstInner, srcInner);
} else {
DrawBoxShadows(destDrawTarget, boxShadow, dstOuter, dstInner,
srcOuter, srcInner, skipRect);
// Middle part
RepeatOrStretchSurface(destDrawTarget, boxShadow,
RectWithEdgesTRBL(dstInner.Y(), dstInner.XMost(),
dstInner.YMost(), dstInner.X()),
RectWithEdgesTRBL(srcInner.Y(), srcInner.XMost(),
srcInner.YMost(), srcInner.X()),
skipRect);
}
// A note about anti-aliasing and seems between adjacent parts:
// We don't explicitly disable anti-aliasing in the DrawSurface calls above,
// so if there's a transform on destDrawTarget that is not pixel-aligned,
// there will be seams between adjacent parts of the box-shadow. It's hard to
// avoid those without the use of an intermediate surface.
// You might think that we could avoid those by just turning of AA, but there
// is a problem with that: Box-shadow rendering needs to clip out the
// element's border box, and we'd like that clip to have anti-aliasing -
// especially if the element has rounded corners! So we can't do that unless
// we have a way to say "Please anti-alias the clip, but don't antialias the
// destination rect of the DrawSurface call".
// On OS X there is an additional problem with turning off AA: CoreGraphics
// will not just fill the pixels that have their pixel center inside the
// filled shape. Instead, it will fill all the pixels which are partially
// covered by the shape. So for pixels on the edge between two adjacent parts,
// all those pixels will be painted to by both parts, which looks very bad.
destDrawTarget.PopClip();
}
