nsIntRect
Layer::CalculateScissorRect(const nsIntRect& aCurrentScissorRect,
const gfxMatrix* aWorldTransform)
{
ContainerLayer* container = GetParent();
NS_ASSERTION(container, "This can't be called on the root!");
// Establish initial clip rect: it's either the one passed in, or
// if the parent has an intermediate surface, it's the extents of that surface.
nsIntRect currentClip;
if (container->UseIntermediateSurface()) {
currentClip.SizeTo(container->GetIntermediateSurfaceRect().Size());
} else {
currentClip = aCurrentScissorRect;
}
const nsIntRect *clipRect = GetEffectiveClipRect();
if (!clipRect)
return currentClip;
if (clipRect->IsEmpty()) {
// We might have a non-translation transform in the container so we can't
// use the code path below.
return nsIntRect(currentClip.TopLeft(), nsIntSize(0, 0));
}
nsIntRect scissor = *clipRect;
if (!container->UseIntermediateSurface()) {
gfxMatrix matrix;
DebugOnly<bool> is2D = container->GetEffectiveTransform().Is2D(&matrix);
// See DefaultComputeEffectiveTransforms below
NS_ASSERTION(is2D && matrix.PreservesAxisAlignedRectangles(),
"Non preserves axis aligned transform with clipped child should have forced intermediate surface");
gfxRect r(scissor.x, scissor.y, scissor.width, scissor.height);
gfxRect trScissor = matrix.TransformBounds(r);
trScissor.Round();
if (!gfxUtils::GfxRectToIntRect(trScissor, &scissor)) {
return nsIntRect(currentClip.TopLeft(), nsIntSize(0, 0));
}
// Find the nearest ancestor with an intermediate surface
do {
container = container->GetParent();
} while (container && !container->UseIntermediateSurface());
}
if (container) {
scissor.MoveBy(-container->GetIntermediateSurfaceRect().TopLeft());
} else if (aWorldTransform) {
gfxRect r(scissor.x, scissor.y, scissor.width, scissor.height);
gfxRect trScissor = aWorldTransform->TransformBounds(r);
trScissor.Round();
if (!gfxUtils::GfxRectToIntRect(trScissor, &scissor))
return nsIntRect(currentClip.TopLeft(), nsIntSize(0, 0));
}
return currentClip.Intersect(scissor);
}
