/**
* Scroll the scroll frame associated with |aContent| to the scroll position
* requested in |aMetrics|.
* The scroll offset in |aMetrics| is updated to reflect the actual scroll
* position.
* The displayport stored in |aMetrics| and the callback-transform stored on
* the content are updated to reflect any difference between the requested
* and actual scroll positions.
*/
static void
ScrollFrame(nsIContent* aContent,
FrameMetrics& aMetrics)
{
// Scroll the window to the desired spot
nsIScrollableFrame* sf = nsLayoutUtils::FindScrollableFrameFor(aMetrics.GetScrollId());
if (sf) {
sf->SetScrollableByAPZ(!aMetrics.IsScrollInfoLayer());
}
bool scrollUpdated = false;
CSSPoint apzScrollOffset = aMetrics.GetScrollOffset();
CSSPoint actualScrollOffset = ScrollFrameTo(sf, apzScrollOffset, scrollUpdated);
if (scrollUpdated) {
if (aMetrics.IsScrollInfoLayer()) {
// In cases where the APZ scroll offset is different from the content scroll
// offset, we want to interpret the margins as relative to the APZ scroll
// offset except when the frame is not scrollable by APZ. Therefore, if the
// layer is a scroll info layer, we leave the margins as-is and they will
// be interpreted as relative to the content scroll offset.
if (nsIFrame* frame = aContent->GetPrimaryFrame()) {
frame->SchedulePaint();
}
} else {
// Correct the display port due to the difference between mScrollOffset and the
// actual scroll offset.
APZCCallbackHelper::AdjustDisplayPortForScrollDelta(aMetrics, actualScrollOffset);
}
} else {
// For whatever reason we couldn't update the scroll offset on the scroll frame,
// which means the data APZ used for its displayport calculation is stale. Fall
// back to a sane default behaviour. Note that we don't tile-align the recentered
// displayport because tile-alignment depends on the scroll position, and the
// scroll position here is out of our control. See bug 966507 comment 21 for a
// more detailed explanation.
RecenterDisplayPort(aMetrics);
}
aMetrics.SetScrollOffset(actualScrollOffset);
// APZ transforms inputs assuming we applied the exact scroll offset it
// requested (|apzScrollOffset|). Since we may not have, record the difference
// between what APZ asked for and what we actually applied, and apply it to
// input events to compensate.
if (aContent) {
CSSPoint scrollDelta = apzScrollOffset - actualScrollOffset;
aContent->SetProperty(nsGkAtoms::apzCallbackTransform, new CSSPoint(scrollDelta),
nsINode::DeleteProperty<CSSPoint>);
}
}
