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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#include "nsPageContentFrame.h"
#include "mozilla/PresShell.h"
#include "mozilla/PresShellInlines.h"
#include "mozilla/StaticPrefs_layout.h"
#include "mozilla/dom/Document.h"
#include "nsContentUtils.h"
#include "nsPageFrame.h"
#include "nsCSSFrameConstructor.h"
#include "nsPresContext.h"
#include "nsGkAtoms.h"
#include "nsLayoutUtils.h"
#include "nsPageSequenceFrame.h"
using namespace mozilla;
nsPageContentFrame* NS_NewPageContentFrame(
PresShell* aPresShell, ComputedStyle* aStyle,
already_AddRefed<const nsAtom> aPageName) {
return new (aPresShell) nsPageContentFrame(
aStyle, aPresShell->GetPresContext(), std::move(aPageName));
void nsPageContentFrame::Reflow(nsPresContext* aPresContext,
ReflowOutput& aReflowOutput,
const ReflowInput& aReflowInput,
nsReflowStatus& aStatus) {
MOZ_ASSERT(aStatus.IsEmpty(), "Caller should pass a fresh reflow status!");
MOZ_ASSERT(mPD, "Need a pointer to nsSharedPageData before reflow starts");
if (GetPrevInFlow() && HasAnyStateBits(NS_FRAME_FIRST_REFLOW)) {
nsresult rv =
if (NS_FAILED(rv)) {
// Set our size up front, since some parts of reflow depend on it
// being already set. Note that the computed height may be
// unconstrained; that's ok. Consumers should watch out for that.
const nsSize maxSize = aReflowInput.ComputedPhysicalSize();
// Writing mode for the page content frame.
const WritingMode pcfWM = aReflowInput.GetWritingMode();
aReflowOutput.ISize(pcfWM) = aReflowInput.ComputedISize();
if (aReflowInput.ComputedBSize() != NS_UNCONSTRAINEDSIZE) {
aReflowOutput.BSize(pcfWM) = aReflowInput.ComputedBSize();
// A PageContentFrame must always have one child: the canvas frame.
// Resize our frame allowing it only to be as big as we are
// XXX Pay attention to the page's border and padding...
if (mFrames.NotEmpty()) {
nsIFrame* const frame = mFrames.FirstChild();
const WritingMode frameWM = frame->GetWritingMode();
const LogicalSize logicalSize(frameWM, maxSize);
ReflowInput kidReflowInput(aPresContext, aReflowInput, frame, logicalSize);
ReflowOutput kidReflowOutput(kidReflowInput);
ReflowChild(frame, aPresContext, kidReflowOutput, kidReflowInput, 0, 0,
ReflowChildFlags::Default, aStatus);
// The document element's background should cover the entire canvas, so
// take into account the combined area and any space taken up by
// absolutely positioned elements
nsMargin padding(0, 0, 0, 0);
// XXXbz this screws up percentage padding (sets padding to zero
// in the percentage padding case)
// This is for shrink-to-fit, and therefore we want to use the
// scrollable overflow, since the purpose of shrink to fit is to
// make the content that ought to be reachable (represented by the
// scrollable overflow) fit in the page.
if (frame->HasOverflowAreas()) {
// The background covers the content area and padding area, so check
// for children sticking outside the child frame's padding edge
nscoord xmost = kidReflowOutput.ScrollableOverflow().XMost();
if (xmost > kidReflowOutput.Width()) {
const nscoord widthToFit =
xmost + padding.right +
const float ratio = float(maxSize.width) / float(widthToFit);
NS_ASSERTION(ratio >= 0.0 && ratio < 1.0,
"invalid shrink-to-fit ratio");
mPD->mShrinkToFitRatio = std::min(mPD->mShrinkToFitRatio, ratio);
// In the case of pdf.js documents, we also want to consider the height,
// so that we don't clip the page in either axis if the aspect ratio of
// the PDF doesn't match the destination.
if (nsContentUtils::IsPDFJS(PresContext()->Document()->GetPrincipal())) {
nscoord ymost = kidReflowOutput.ScrollableOverflow().YMost();
if (ymost > kidReflowOutput.Height()) {
const nscoord heightToFit =
ymost + padding.bottom +
const float ratio = float(maxSize.height) / float(heightToFit);
MOZ_ASSERT(ratio >= 0.0 && ratio < 1.0);
mPD->mShrinkToFitRatio = std::min(mPD->mShrinkToFitRatio, ratio);
// pdf.js pages should never overflow given the scaling above.
// nsPrintJob::SetupToPrintContent ignores some ratios close to 1.0
// though and doesn't reflow us again in that case, so we need to clear
// the overflow area here in case that happens. (bug 1689789)
kidReflowOutput.mOverflowAreas = aReflowOutput.mOverflowAreas;
// Place and size the child
FinishReflowChild(frame, aPresContext, kidReflowOutput, &kidReflowInput, 0,
0, ReflowChildFlags::Default);
NS_ASSERTION(aPresContext->IsDynamic() || !aStatus.IsFullyComplete() ||
"bad child flow list");
// Reflow our fixed frames
nsReflowStatus fixedStatus;
ReflowAbsoluteFrames(aPresContext, aReflowOutput, aReflowInput, fixedStatus);
"fixed frames can be truncated, but not incomplete");
if (StaticPrefs::layout_display_list_improve_fragmentation() &&
mFrames.NotEmpty()) {
auto* const previous =
const nscoord previousPageOverflow =
previous ? previous->mRemainingOverflow : 0;
const nsSize containerSize(aReflowInput.AvailableWidth(),
const nscoord pageBSize = GetLogicalRect(containerSize).BSize(pcfWM);
const nscoord overflowBSize =
LogicalRect(pcfWM, ScrollableOverflowRect(), GetSize()).BEnd(pcfWM);
const nscoord currentPageOverflow = overflowBSize - pageBSize;
nscoord remainingOverflow =
std::max(currentPageOverflow, previousPageOverflow - pageBSize);
if (aStatus.IsFullyComplete() && remainingOverflow > 0) {
// If we have ScrollableOverflow off the end of our page, then we report
// ourselves as overflow-incomplete in order to produce an additional
// content-less page, which we expect to draw our overflow on our behalf.
mRemainingOverflow = std::max(remainingOverflow, 0);
using PageAndOffset = std::pair<nsPageContentFrame*, nscoord>;
// Returns the previous continuation PageContentFrames that have overflow areas,
// and their offsets to the top of the given PageContentFrame |aPage|. Since the
// iteration is done backwards, the returned pages are arranged in descending
// order of page number.
static nsTArray<PageAndOffset> GetPreviousPagesWithOverflow(
nsPageContentFrame* aPage) {
nsTArray<PageAndOffset> pages(8);
auto GetPreviousPageContentFrame = [](nsPageContentFrame* aPageCF) {
nsIFrame* prevCont = aPageCF->GetPrevContinuation();
MOZ_ASSERT(!prevCont || prevCont->IsPageContentFrame(),
"Expected nsPageContentFrame or nullptr");
return static_cast<nsPageContentFrame*>(prevCont);
nsPageContentFrame* pageCF = aPage;
// The collective height of all prev-continuations we've traversed so far:
nscoord offsetToCurrentPageBStart = 0;
const auto wm = pageCF->GetWritingMode();
while ((pageCF = GetPreviousPageContentFrame(pageCF))) {
offsetToCurrentPageBStart += pageCF->BSize(wm);
if (pageCF->HasOverflowAreas()) {
pages.EmplaceBack(pageCF, offsetToCurrentPageBStart);
return pages;
static void BuildPreviousPageOverflow(nsDisplayListBuilder* aBuilder,
nsPageFrame* aPageFrame,
nsPageContentFrame* aCurrentPageCF,
const nsDisplayListSet& aLists) {
const auto previousPagesAndOffsets =
const auto wm = aCurrentPageCF->GetWritingMode();
for (const PageAndOffset& pair : Reversed(previousPagesAndOffsets)) {
auto* prevPageCF = pair.first;
const nscoord offsetToCurrentPageBStart = pair.second;
// Only scrollable overflow create new pages, not ink overflow.
const LogicalRect scrollableOverflow(
wm, prevPageCF->ScrollableOverflowRectRelativeToSelf(),
const auto remainingOverflow =
scrollableOverflow.BEnd(wm) - offsetToCurrentPageBStart;
if (remainingOverflow <= 0) {
// This rect represents the piece of prevPageCF's overflow that ends up on
// the current pageContentFrame (in prevPageCF's coordinate system).
// Note that we use InkOverflow here since this is for painting.
LogicalRect overflowRect(wm, prevPageCF->InkOverflowRectRelativeToSelf(),
overflowRect.BStart(wm) = offsetToCurrentPageBStart;
overflowRect.BSize(wm) = std::min(remainingOverflow, prevPageCF->BSize(wm));
// Convert the overflowRect to the coordinate system of aPageFrame, and
// set it as the visible rect for display list building.
const nsRect visibleRect =
overflowRect.GetPhysicalRect(wm, prevPageCF->GetSize()) +
nsDisplayListBuilder::AutoBuildingDisplayList buildingForChild(
aBuilder, aPageFrame, visibleRect, visibleRect);
// This part is tricky. Because display items are positioned based on the
// frame tree, building a display list for the previous page yields
// display items that are outside of the current page bounds.
// To fix that, an additional reference frame offset is added, which
// shifts the display items down (block axis) as if the current and
// previous page were one long page in the same coordinate system.
const nsSize containerSize = aPageFrame->GetSize();
LogicalPoint pageOffset(wm, aCurrentPageCF->GetOffsetTo(prevPageCF),
pageOffset.B(wm) -= offsetToCurrentPageBStart;
pageOffset.GetPhysicalPoint(wm, containerSize));
aPageFrame->BuildDisplayListForChild(aBuilder, prevPageCF, aLists);
* Remove all leaf display items that are not for descendants of
* aBuilder->GetReferenceFrame() from aList.
* @param aPage the page we're constructing the display list for
* @param aList the list that is modified in-place
static void PruneDisplayListForExtraPage(nsDisplayListBuilder* aBuilder,
nsPageFrame* aPage,
nsDisplayList* aList) {
for (nsDisplayItem* i : aList->TakeItems()) {
if (!i) break;
nsDisplayList* subList = i->GetSameCoordinateSystemChildren();
if (subList) {
PruneDisplayListForExtraPage(aBuilder, aPage, subList);
} else {
nsIFrame* f = i->Frame();
if (!nsLayoutUtils::IsProperAncestorFrameCrossDocInProcess(aPage, f)) {
// We're throwing this away so call its destructor now. The memory
// is owned by aBuilder which destroys all items at once.
static void BuildDisplayListForExtraPage(nsDisplayListBuilder* aBuilder,
nsPageFrame* aPage,
nsIFrame* aExtraPage,
nsDisplayList* aList) {
// The only content in aExtraPage we care about is out-of-flow content from
// aPage, whose placeholders have occurred in aExtraPage. If
// NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO is not set, then aExtraPage has
// no such content.
nsDisplayList list(aBuilder);
aExtraPage->BuildDisplayListForStackingContext(aBuilder, &list);
PruneDisplayListForExtraPage(aBuilder, aPage, &list);
static gfx::Matrix4x4 ComputePageContentTransform(const nsIFrame* aFrame,
float aAppUnitsPerPixel) {
float scale = aFrame->PresContext()->GetPageScale();
return gfx::Matrix4x4::Scaling(scale, scale, 1);
nsIFrame::ComputeTransformFunction nsPageContentFrame::GetTransformGetter()
const {
return ComputePageContentTransform;
void nsPageContentFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
const nsDisplayListSet& aLists) {
auto* pageFrame = static_cast<nsPageFrame*>(GetParent());
auto pageNum = pageFrame->GetPageNum();
NS_ASSERTION(pageNum <= 255, "Too many pages to handle OOFs");
if (aBuilder->GetBuildingExtraPagesForPageNum()) {
return mozilla::ViewportFrame::BuildDisplayList(aBuilder, aLists);
nsDisplayListCollection set(aBuilder);
nsDisplayList content(aBuilder);
const nsRect clipRect(aBuilder->ToReferenceFrame(this), GetSize());
DisplayListClipState::AutoSaveRestore clipState(aBuilder);
// Overwrite current clip, since we're going to wrap in a transform and the
// current clip is no longer meaningful.
if (StaticPrefs::layout_display_list_improve_fragmentation() &&
pageNum <= 255) {
nsDisplayListBuilder::AutoPageNumberSetter p(aBuilder, pageNum);
BuildPreviousPageOverflow(aBuilder, pageFrame, this, set);
mozilla::ViewportFrame::BuildDisplayList(aBuilder, set);
set.SerializeWithCorrectZOrder(&content, GetContent());
// We may need to paint out-of-flow frames whose placeholders are on other
// pages. Add those pages to our display list. Note that out-of-flow frames
// can't be placed after their placeholders so
// we don't have to process earlier pages. The display lists for
// these extra pages are pruned so that only display items for the
// page we currently care about (which we would have reached by
// following placeholders to their out-of-flows) end up on the list.
// Stacking context frames that wrap content on their normal page,
// as well as OOF content for this page will have their container
// items duplicated. We tell the builder to include our page number
// in the unique key for any extra page items so that they can be
// differentiated from the ones created on the normal page.
if (pageNum <= 255) {
const nsRect overflowRect = ScrollableOverflowRectRelativeToSelf();
nsDisplayListBuilder::AutoPageNumberSetter p(aBuilder, pageNum);
// The static_cast here is technically unnecessary, but it helps
// devirtualize the GetNextContinuation() function call if pcf has a
// concrete type (with an inherited `final` GetNextContinuation() impl).
auto* pageCF = this;
while ((pageCF = static_cast<nsPageContentFrame*>(
pageCF->GetNextContinuation()))) {
nsRect childVisible = overflowRect + GetOffsetTo(pageCF);
nsDisplayListBuilder::AutoBuildingDisplayList buildingForChild(
aBuilder, pageCF, childVisible, childVisible);
BuildDisplayListForExtraPage(aBuilder, pageFrame, pageCF, &content);
// Add the canvas background color to the bottom of the list. This
// happens after we've built the list so that AddCanvasBackgroundColorItem
// can monkey with the contents if necessary.
const nsRect backgroundRect(aBuilder->ToReferenceFrame(this), GetSize());
aBuilder, &content, this, backgroundRect, NS_RGBA(0, 0, 0, 0));
aBuilder, this, &content, content.GetBuildingRect(),
void nsPageContentFrame::AppendDirectlyOwnedAnonBoxes(
nsTArray<OwnedAnonBox>& aResult) {
"pageContentFrame must have a canvasFrame child");
void nsPageContentFrame::EnsurePageName() {
"Should only have been called on first reflow");
if (mPageName) {
"Only the first page should initially have a null page name.");
// This was the first page, we need to find our own page name and then set
// our computed style based on that.
mPageName = ComputePageValue();
MOZ_ASSERT(mPageName, "Page name should never be null");
// Resolve the computed style given this page-name and the :first pseudo.
RefPtr<ComputedStyle> pageContentPseudoStyle =
mPageName, StylePagePseudoClassFlags::FIRST);
nsresult nsPageContentFrame::GetFrameName(nsAString& aResult) const {
return MakeFrameName(u"PageContent"_ns, aResult);
void nsPageContentFrame::ExtraContainerFrameInfo(nsACString& aTo) const {
if (mPageName) {
aTo += " [page=";
aTo += nsAtomCString(mPageName);
aTo += "]";