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Bug 1779645 Part 1 - Switch CSS named page fragmentation to happen at reflow instead of frame construction r=dholbert

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This also adds a small post-processing step for frame-construction to ensure
that replaced frames (or more generally frames with content but no children)
have the auto page-name set on them.

When page-name value tracking is switched to be lazy, this post-processing step
will likely be redundant and can be removed.

Differential Revision: https://phabricator.services.mozilla.com/D152701
This commit is contained in:
Emily McDonough
2022-09-12 22:44:48 +00:00
parent 334a736b2a
commit e114010ff0
3 changed files with 152 additions and 83 deletions
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70
layout/generic/nsBlockFrame.cpp
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@@ -2626,6 +2626,29 @@ void nsBlockFrame::ReflowDirtyLines(BlockReflowState& aState) {
LineIterator line = LinesBegin(), line_end = LinesEnd();
// Determine if children of this frame could have breaks between them for
// page names.
//
// We need to check for paginated layout, the named-page pref, and if the
// available block-size is constrained.
//
// Note that we need to check for paginated layout as named-pages are only
// used during paginated reflow. We need to additionally check for
// unconstrained block-size to avoid introducing fragmentation breaks during
// "measuring" reflows within an overall paginated reflow, and to avoid
// fragmentation in monolithic containers like 'inline-block'.
//
// Because we can only break for named pages using Class A breakpoints, we
// also need to check that the block flow direction of the containing frame
// of these items (which is this block) is parallel to that of this page.
// See: https://www.w3.org/TR/css-break-3/#btw-blocks
const nsPresContext* const presCtx = aState.mPresContext;
const bool canBreakForPageNames =
aState.mReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE &&
presCtx->IsPaginated() && StaticPrefs::layout_css_named_pages_enabled() &&
presCtx->GetPresShell()->GetRootFrame()->GetWritingMode().IsVertical() ==
GetWritingMode().IsVertical();
// Reflow the lines that are already ours
for (; line != line_end; ++line, aState.AdvanceToNextLine()) {
DumpLine(aState, line, deltaBCoord, 0);
@@ -2779,6 +2802,38 @@ void nsBlockFrame::ReflowDirtyLines(BlockReflowState& aState) {
}
}
// Check for a page break caused by CSS named pages.
//
// We should break for named pages when two frames meet at a class A
// breakpoint, where the first frame has a different end page value to the
// second frame's start page value. canBreakForPageNames is true iff
// children of this frame can form class A breakpoints, and that we are not
// in a measurement reflow or in a monolithic container such as
// 'inline-block'.
//
// We specifically do not want to cause a page-break for named pages when
// we are at the top of a page. This would otherwise happen when the
// previous sibling is an nsPageBreakFrame, or all previous siblings on the
// current page are zero-height. The latter may not be per-spec, but is
// compatible with Chrome's implementation of named pages.
bool shouldBreakForPageName = false;
if (canBreakForPageNames && (!aState.mReflowInput.mFlags.mIsTopOfPage ||
!aState.IsAdjacentWithBStart())) {
const nsIFrame* const frame = line->mFirstChild;
if (const nsIFrame* prevFrame = frame->GetPrevSibling()) {
if (const nsIFrame::PageValues* const pageValues =
frame->GetProperty(nsIFrame::PageValuesProperty())) {
const nsIFrame::PageValues* const prevPageValues =
prevFrame->GetProperty(nsIFrame::PageValuesProperty());
if (prevPageValues &&
prevPageValues->mEndPageValue != pageValues->mStartPageValue) {
shouldBreakForPageName = true;
line->MarkDirty();
}
}
}
}
if (needToRecoverState && line->IsDirty()) {
// We need to reconstruct the block-end margin only if we didn't
// reflow the previous line and we do need to reflow (or repair
@@ -2826,9 +2881,18 @@ void nsBlockFrame::ReflowDirtyLines(BlockReflowState& aState) {
"Don't reflow blocks while willReflowAgain is true, reflow "
"of block abs-pos children depends on this");
// Reflow the dirty line. If it's an incremental reflow, then force
// it to invalidate the dirty area if necessary
ReflowLine(aState, line, &keepGoing);
if (shouldBreakForPageName) {
// Immediately fragment for page-name. It is possible we could break
// out of the loop right here, but this should make it more similar to
// what happens when reflow causes fragmentation.
keepGoing = false;
PushLines(aState, line.prev());
aState.mReflowStatus.SetIncomplete();
} else {
// Reflow the dirty line. If it's an incremental reflow, then force
// it to invalidate the dirty area if necessary
ReflowLine(aState, line, &keepGoing);
}
if (aState.mReflowInput.WillReflowAgainForClearance()) {
line->MarkDirty();