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Bug 1241917 - Restrict subframe's displayport base to root composition bounds. r=tn

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Previously displayport bases were computed as the intersection of the
scrollport with the dirtyrect. However the dirtyrect covers what is
rendered, and with displayports what we render can be much larger than
what is visible. With displayport bases intended to represent what was
visible, this was a problem. By restricting them to the root composition
size this makes them more closely match what is visible. To do this more
properly we'd want to intersect the dirtyrect with the scroll clip of
every ancestor scroll frame, not just the root composition bounds.
This commit is contained in:
Jamie Nicol 2016-02-04 17:53:56 +00:00
parent 3585a95d3a
commit d412b3daee
1 changed files with 25 additions and 2 deletions
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27
layout/generic/nsGfxScrollFrame.cpp
View File

@ -3346,9 +3346,32 @@ ScrollFrameHelper::DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
displayportBase =
nsRect(nsPoint(0, 0), nsLayoutUtils::CalculateCompositionSizeForFrame(mOuter));
} else {
// Restrict the dirty rect to the scrollport, and make it relative to the
// scrollport for the displayport base.
// Make the displayport base equal to the dirty rect restricted to
// the scrollport and the root composition bounds, relative to the
// scrollport.
displayportBase = aDirtyRect->Intersect(mScrollPort);
const nsPresContext* rootPresContext =
pc->GetToplevelContentDocumentPresContext();
if (!rootPresContext) {
rootPresContext = pc->GetRootPresContext();
}
if (rootPresContext) {
const nsIPresShell* const rootPresShell = rootPresContext->PresShell();
nsIFrame* rootFrame = rootPresShell->GetRootScrollFrame();
if (!rootFrame) {
rootFrame = rootPresShell->GetRootFrame();
}
if (rootFrame) {
nsRect rootCompBounds =
nsRect(nsPoint(0, 0), nsLayoutUtils::CalculateCompositionSizeForFrame(rootFrame));
nsLayoutUtils::TransformRect(rootFrame, mOuter, rootCompBounds);
displayportBase = displayportBase.Intersect(rootCompBounds);
}
}
displayportBase -= mScrollPort.TopLeft();
}