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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 "nsPageFrame.h"
#include "mozilla/AppUnits.h"
#include "mozilla/PresShell.h"
#include "mozilla/StaticPrefs_layout.h"
#include "mozilla/gfx/2D.h"
#include "gfxContext.h"
#include "nsDeviceContext.h"
#include "nsFontMetrics.h"
#include "nsIFrame.h"
#include "nsLayoutUtils.h"
#include "nsPresContext.h"
#include "nsGkAtoms.h"
#include "nsFieldSetFrame.h"
#include "nsPageContentFrame.h"
#include "nsDisplayList.h"
#include "nsPageSequenceFrame.h" // for nsSharedPageData
#include "nsTextFormatter.h" // for page number localization formatting
#include "nsBidiUtils.h"
#include "nsIPrintSettings.h"
#include "mozilla/Logging.h"
extern mozilla::LazyLogModule gLayoutPrintingLog;
#define PR_PL(_p1) MOZ_LOG(gLayoutPrintingLog, mozilla::LogLevel::Debug, _p1)
using namespace mozilla;
using namespace mozilla::gfx;
nsPageFrame* NS_NewPageFrame(PresShell* aPresShell, ComputedStyle* aStyle) {
return new (aPresShell) nsPageFrame(aStyle, aPresShell->GetPresContext());
nsPageFrame::nsPageFrame(ComputedStyle* aStyle, nsPresContext* aPresContext)
: nsContainerFrame(aStyle, aPresContext, kClassID) {}
nsPageFrame::~nsPageFrame() = default;
nsReflowStatus nsPageFrame::ReflowPageContent(
nsPresContext* aPresContext, const ReflowInput& aPageReflowInput) {
// XXX Pay attention to the page's border and padding...
// Reflow our ::-moz-page-content frame, allowing it only to be as big as we
// are (minus margins).
if (mFrames.IsEmpty()) {
return {};
nsIFrame* frame = mFrames.FirstChild();
nsSize maxSize = aPresContext->GetPageSize();
float scale = aPresContext->GetPageScale();
// When the reflow size is NS_UNCONSTRAINEDSIZE it means we are reflowing
// a single page to print selection. So this means we want to use
// NS_UNCONSTRAINEDSIZE without altering it.
// FIXME(emilio): Is this still true?
maxSize.width = NSToCoordCeil(maxSize.width / scale);
if (maxSize.height != NS_UNCONSTRAINEDSIZE) {
maxSize.height = NSToCoordCeil(maxSize.height / scale);
// Get the number of Twips per pixel from the PresContext
const nscoord onePixel = AppUnitsPerCSSPixel();
// insurance against infinite reflow, when reflowing less than a pixel
// XXX Shouldn't we do something more friendly when invalid margins
// are set?
if (maxSize.width < onePixel || maxSize.height < onePixel) {
NS_WARNING("Reflow aborted; no space for content");
return {};
ReflowInput kidReflowInput(aPresContext, aPageReflowInput, frame,
LogicalSize(frame->GetWritingMode(), maxSize));
kidReflowInput.mFlags.mIsTopOfPage = true;
kidReflowInput.mFlags.mTableIsSplittable = true;
mPageContentMargin = aPresContext->GetDefaultPageMargin();
// Use the margins given in the @page rule if told to do so.
// We clamp to the paper's unwriteable margins to avoid clipping, *except*
// that we will respect a margin of zero if specified, assuming this means
// the document is intended to fit the paper size exactly, and the client is
// taking full responsibility for what happens around the edges.
if (mPD->mPrintSettings->GetHonorPageRuleMargins()) {
const auto& margin = kidReflowInput.mStyleMargin->mMargin;
for (const auto side : mozilla::AllPhysicalSides()) {
if (!margin.Get(side).IsAuto()) {
nscoord computed = kidReflowInput.ComputedPhysicalMargin().Side(side);
// Respecting a zero margin is particularly important when the client
// is PDF.js where the PDF already contains the margins.
if (computed == 0) {
mPageContentMargin.Side(side) = 0;
} else {
nscoord unwriteable = nsPresContext::CSSTwipsToAppUnits(
mPageContentMargin.Side(side) = std::max(
kidReflowInput.ComputedPhysicalMargin().Side(side), unwriteable);
nscoord maxWidth = maxSize.width - mPageContentMargin.LeftRight() / scale;
nscoord maxHeight;
if (maxSize.height == NS_UNCONSTRAINEDSIZE) {
} else {
maxHeight = maxSize.height - mPageContentMargin.TopBottom() / scale;
// Check the width and height, if they're too small we reset the margins
// back to the default.
if (maxWidth < onePixel || maxHeight < onePixel) {
mPageContentMargin = aPresContext->GetDefaultPageMargin();
maxWidth = maxSize.width - mPageContentMargin.LeftRight() / scale;
if (maxHeight != NS_UNCONSTRAINEDSIZE) {
maxHeight = maxSize.height - mPageContentMargin.TopBottom() / scale;
// And if they're still too small, we give up.
if (maxWidth < onePixel || maxHeight < onePixel) {
NS_WARNING("Reflow aborted; no space for content");
return {};
// calc location of frame
nscoord xc = mPageContentMargin.left;
nscoord yc =;
// Get the child's desired size
ReflowOutput kidOutput(kidReflowInput);
nsReflowStatus kidStatus;
ReflowChild(frame, aPresContext, kidOutput, kidReflowInput, xc, yc,
ReflowChildFlags::Default, kidStatus);
// Place and size the child
FinishReflowChild(frame, aPresContext, kidOutput, &kidReflowInput, xc, yc,
NS_ASSERTION(!kidStatus.IsFullyComplete() || !frame->GetNextInFlow(),
"bad child flow list");
return kidStatus;
void nsPageFrame::Reflow(nsPresContext* aPresContext,
ReflowOutput& aReflowOutput,
const ReflowInput& aReflowInput,
nsReflowStatus& aStatus) {
DISPLAY_REFLOW(aPresContext, this, aReflowInput, aReflowOutput, aStatus);
MOZ_ASSERT(aStatus.IsEmpty(), "Caller should pass a fresh reflow status!");
MOZ_ASSERT(mPD, "Need a pointer to nsSharedPageData before reflow starts");
mFrames.FirstChild() && mFrames.FirstChild()->IsPageContentFrame(),
"pageFrame must have a pageContentFrame child");
// Our status is the same as our child's.
aStatus = ReflowPageContent(aPresContext, aReflowInput);
PR_PL(("PageFrame::Reflow %p ", this));
PR_PL(("[%d,%d][%d,%d]\n", aReflowOutput.Width(), aReflowOutput.Height(),
aReflowInput.AvailableWidth(), aReflowInput.AvailableHeight()));
// Return our desired size
WritingMode wm = aReflowInput.GetWritingMode();
aReflowOutput.ISize(wm) = aReflowInput.AvailableISize();
if (aReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE) {
aReflowOutput.BSize(wm) = aReflowInput.AvailableBSize();
PR_PL(("PageFrame::Reflow %p ", this));
PR_PL(("[%d,%d]\n", aReflowInput.AvailableWidth(),
NS_FRAME_SET_TRUNCATION(aStatus, aReflowInput, aReflowOutput);
nsresult nsPageFrame::GetFrameName(nsAString& aResult) const {
return MakeFrameName(u"Page"_ns, aResult);
void nsPageFrame::ProcessSpecialCodes(const nsString& aStr, nsString& aNewStr) {
aNewStr = aStr;
// Search to see if the &D code is in the string
// then subst in the current date/time
constexpr auto kDate = u"&D"_ns;
if (aStr.Find(kDate) != kNotFound) {
aNewStr.ReplaceSubstring(kDate, mPD->mDateTimeStr);
// NOTE: Must search for &PT before searching for &P
// Search to see if the "page number and page" total code are in the string
// and replace the page number and page total code with the actual
// values
constexpr auto kPageAndTotal = u"&PT"_ns;
if (aStr.Find(kPageAndTotal) != kNotFound) {
nsAutoString uStr;
nsTextFormatter::ssprintf(uStr, mPD->mPageNumAndTotalsFormat.get(),
mPageNum, mPD->mRawNumPages);
aNewStr.ReplaceSubstring(kPageAndTotal, uStr);
// Search to see if the page number code is in the string
// and replace the page number code with the actual value
constexpr auto kPage = u"&P"_ns;
if (aStr.Find(kPage) != kNotFound) {
nsAutoString uStr;
nsTextFormatter::ssprintf(uStr, mPD->mPageNumFormat.get(), mPageNum);
aNewStr.ReplaceSubstring(kPage, uStr);
constexpr auto kTitle = u"&T"_ns;
if (aStr.Find(kTitle) != kNotFound) {
aNewStr.ReplaceSubstring(kTitle, mPD->mDocTitle);
constexpr auto kDocURL = u"&U"_ns;
if (aStr.Find(kDocURL) != kNotFound) {
aNewStr.ReplaceSubstring(kDocURL, mPD->mDocURL);
constexpr auto kPageTotal = u"&L"_ns;
if (aStr.Find(kPageTotal) != kNotFound) {
nsAutoString uStr;
nsTextFormatter::ssprintf(uStr, mPD->mPageNumFormat.get(),
aNewStr.ReplaceSubstring(kPageTotal, uStr);
nscoord nsPageFrame::GetXPosition(gfxContext& aRenderingContext,
nsFontMetrics& aFontMetrics,
const nsRect& aRect, int32_t aJust,
const nsString& aStr) {
nscoord width = nsLayoutUtils::AppUnitWidthOfStringBidi(
aStr, this, aFontMetrics, aRenderingContext);
nscoord x = aRect.x;
switch (aJust) {
case nsIPrintSettings::kJustLeft:
x += mPD->mEdgePaperMargin.left;
case nsIPrintSettings::kJustCenter:
x += (aRect.width - width) / 2;
case nsIPrintSettings::kJustRight:
x += aRect.width - width - mPD->mEdgePaperMargin.right;
} // switch
return x;
// Draw a header or footer
// @param aRenderingContext - rendering content to draw into
// @param aHeaderFooter - indicates whether it is a header or footer
// @param aStrLeft - string for the left header or footer; can be empty
// @param aStrCenter - string for the center header or footer; can be empty
// @param aStrRight - string for the right header or footer; can be empty
// @param aRect - the rect of the page
// @param aAscent - the ascent of the font
// @param aHeight - the height of the font
void nsPageFrame::DrawHeaderFooter(
gfxContext& aRenderingContext, nsFontMetrics& aFontMetrics,
nsHeaderFooterEnum aHeaderFooter, const nsString& aStrLeft,
const nsString& aStrCenter, const nsString& aStrRight, const nsRect& aRect,
nscoord aAscent, nscoord aHeight) {
int32_t numStrs = 0;
if (!aStrLeft.IsEmpty()) numStrs++;
if (!aStrCenter.IsEmpty()) numStrs++;
if (!aStrRight.IsEmpty()) numStrs++;
if (numStrs == 0) return;
nscoord strSpace = aRect.width / numStrs;
if (!aStrLeft.IsEmpty()) {
DrawHeaderFooter(aRenderingContext, aFontMetrics, aHeaderFooter,
nsIPrintSettings::kJustLeft, aStrLeft, aRect, aAscent,
aHeight, strSpace);
if (!aStrCenter.IsEmpty()) {
DrawHeaderFooter(aRenderingContext, aFontMetrics, aHeaderFooter,
nsIPrintSettings::kJustCenter, aStrCenter, aRect, aAscent,
aHeight, strSpace);
if (!aStrRight.IsEmpty()) {
DrawHeaderFooter(aRenderingContext, aFontMetrics, aHeaderFooter,
nsIPrintSettings::kJustRight, aStrRight, aRect, aAscent,
aHeight, strSpace);
// Draw a header or footer string
// @param aRenderingContext - rendering context to draw into
// @param aHeaderFooter - indicates whether it is a header or footer
// @param aJust - indicates where the string is located within the header/footer
// @param aStr - the string to be drawn
// @param aRect - the rect of the page
// @param aHeight - the height of the font
// @param aAscent - the ascent of the font
// @param aWidth - available width for the string
void nsPageFrame::DrawHeaderFooter(gfxContext& aRenderingContext,
nsFontMetrics& aFontMetrics,
nsHeaderFooterEnum aHeaderFooter,
int32_t aJust, const nsString& aStr,
const nsRect& aRect, nscoord aAscent,
nscoord aHeight, nscoord aWidth) {
nscoord contentWidth =
aWidth - (mPD->mEdgePaperMargin.left + mPD->mEdgePaperMargin.right);
DrawTarget* drawTarget = aRenderingContext.GetDrawTarget();
if ((aHeaderFooter == eHeader && aHeight < ||
(aHeaderFooter == eFooter && aHeight < mPageContentMargin.bottom)) {
nsAutoString str;
ProcessSpecialCodes(aStr, str);
int32_t indx;
int32_t textWidth = 0;
const char16_t* text = str.get();
int32_t len = (int32_t)str.Length();
if (len == 0) {
return; // bail is empty string
// find how much text fits, the "position" is the size of the available area
if (nsLayoutUtils::BinarySearchForPosition(
drawTarget, aFontMetrics, text, 0, 0, 0, len, int32_t(contentWidth),
indx, textWidth)) {
if (indx < len - 1) {
// we can't fit in all the text
if (indx > 3) {
// But we can fit in at least 4 chars. Show all but 3 of them, then
// an ellipsis.
// XXXbz for non-plane0 text, this may be cutting things in the
// middle of a codepoint! Also, we have no guarantees that the three
// dots will fit in the space the three chars we removed took up with
// these font metrics!
str.Truncate(indx - 3);
} else {
// We can only fit 3 or fewer chars. Just show nothing
} else {
return; // bail if couldn't find the correct length
if (HasRTLChars(str)) {
// calc the x and y positions of the text
nscoord x =
GetXPosition(aRenderingContext, aFontMetrics, aRect, aJust, str);
nscoord y;
if (aHeaderFooter == eHeader) {
y = aRect.y + mPD->;
} else {
y = aRect.YMost() - aHeight - mPD->mEdgePaperMargin.bottom;
// set up new clip and draw the text
aRect, PresContext()->AppUnitsPerDevPixel(), *drawTarget));
nsLayoutUtils::DrawString(this, aFontMetrics, &aRenderingContext, str.get(),
str.Length(), nsPoint(x, y + aAscent), nullptr,
* 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 aExtraPage the page we constructed aList for
* @param aList the list that is modified in-place
static void PruneDisplayListForExtraPage(nsDisplayListBuilder* aBuilder,
nsPageFrame* aPage,
nsIFrame* aExtraPage,
nsDisplayList* aList) {
nsDisplayList newList;
while (true) {
nsDisplayItem* i = aList->RemoveBottom();
if (!i) break;
nsDisplayList* subList = i->GetSameCoordinateSystemChildren();
if (subList) {
PruneDisplayListForExtraPage(aBuilder, aPage, aExtraPage, subList);
} else {
nsIFrame* f = i->Frame();
if (!nsLayoutUtils::IsProperAncestorFrameCrossDoc(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;
aExtraPage->BuildDisplayListForStackingContext(aBuilder, &list);
PruneDisplayListForExtraPage(aBuilder, aPage, aExtraPage, &list);
static gfx::Matrix4x4 ComputePageTransform(nsIFrame* aFrame,
float aAppUnitsPerPixel) {
float scale = aFrame->PresContext()->GetPageScale();
return gfx::Matrix4x4::Scaling(scale, scale, 1);
class nsDisplayHeaderFooter final : public nsPaintedDisplayItem {
nsDisplayHeaderFooter(nsDisplayListBuilder* aBuilder, nsPageFrame* aFrame)
: nsPaintedDisplayItem(aBuilder, aFrame) {
virtual void Paint(nsDisplayListBuilder* aBuilder,
gfxContext* aCtx) override {
#ifdef DEBUG
nsPageFrame* pageFrame = do_QueryFrame(mFrame);
MOZ_ASSERT(pageFrame, "We should have an nsPageFrame");
*aCtx, ToReferenceFrame(), IsSubpixelAADisabled());
virtual nsRect GetComponentAlphaBounds(
nsDisplayListBuilder* aBuilder) const override {
bool snap;
return GetBounds(aBuilder, &snap);
static void PaintMarginGuides(nsIFrame* aFrame, DrawTarget* aDrawTarget,
const nsRect& aDirtyRect, nsPoint aPt) {
// Set up parameters needed to draw the guides: we draw them in blue,
// using 2px-long dashes with 2px separation and a line width of 0.5px.
// Drawing is antialiased, so on a non-hidpi screen where the line width is
// less than one device pixel, it doesn't disappear but renders fainter
// than a solid 1px-wide line would be.
// (In many cases, the entire preview is scaled down so that the guides
// will be nominally less than 1 dev px even on a hidpi screen, resulting
// in lighter antialiased rendering so they don't dominate the page.)
ColorPattern pattern(ToDeviceColor(sRGBColor(0.0f, 0.0f, 1.0f)));
Float dashes[] = {2.0f, 2.0f};
StrokeOptions stroke(/* line width (in CSS px) */ 0.5f,
JoinStyle::MITER_OR_BEVEL, CapStyle::BUTT,
/* mitre limit (default, not used) */ 10.0f,
/* set dash pattern of 2px stroke, 2px gap */
ArrayLength(dashes), dashes,
/* dash offset */ 0.0f);
DrawOptions options;
const nsMargin& margin =
int32_t appUnitsPerDevPx = aFrame->PresContext()->AppUnitsPerDevPixel();
// Get the frame's rect and inset by the margins to get the edges of the
// content area, where we want to draw the guides.
// We draw in two stages, first applying the top/bottom margins and drawing
// the horizontal guides across the full width of the page.
nsRect rect(aPt, aFrame->GetSize());
rect.Deflate(nsMargin(, 0, margin.bottom, 0));
Rect r = NSRectToRect(rect, appUnitsPerDevPx);
aDrawTarget->StrokeLine(r.TopLeft(), r.TopRight(), pattern, stroke, options);
aDrawTarget->StrokeLine(r.BottomLeft(), r.BottomRight(), pattern, stroke,
// Then reset rect, apply the left/right margins, and draw vertical guides
// extending the full height of the page.
rect = nsRect(aPt, aFrame->GetSize());
rect.Deflate(nsMargin(0, margin.right, 0, margin.left));
r = NSRectToRect(rect, appUnitsPerDevPx);
aDrawTarget->StrokeLine(r.TopLeft(), r.BottomLeft(), pattern, stroke,
aDrawTarget->StrokeLine(r.TopRight(), r.BottomRight(), pattern, stroke,
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, aPageFrame->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);
void nsPageFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
const nsDisplayListSet& aLists) {
nsDisplayListCollection set(aBuilder);
nsPresContext* pc = PresContext();
nsIFrame* child = mFrames.FirstChild();
float scale = pc->GetPageScale();
nsRect clipRect(nsPoint(0, 0), child->GetSize());
// Note: this computation matches how we compute maxSize.height
// in nsPageFrame::Reflow
nscoord expectedPageContentHeight = NSToCoordCeil(GetSize().height / scale);
if (clipRect.height > expectedPageContentHeight) {
// We're doing print-selection, with one long page-content frame.
// Clip to the appropriate page-content slice for the current page.
NS_ASSERTION(mPageNum > 0, "page num should be positive");
// Note: The pageContentFrame's y-position has been set such that a zero
// y-value matches the top edge of the current page. So, to clip to the
// current page's content (in coordinates *relative* to the page content
// frame), we just negate its y-position and add the top margin.
// FIXME(emilio): Rather than the default margin, this should probably use
// mPageContentMargin?
clipRect.y = NSToCoordCeil(
(-child->GetRect().y + pc->GetDefaultPageMargin().top) / scale);
clipRect.height = expectedPageContentHeight;
NS_ASSERTION(clipRect.y < child->GetSize().height,
"Should be clipping to region inside the page content bounds");
clipRect += aBuilder->ToReferenceFrame(child);
nsDisplayList content;
DisplayListClipState::AutoSaveRestore clipState(aBuilder);
// Overwrite current clip, since we're going to wrap in a transform
// and the current clip is no longer meaningful.
MOZ_ASSERT(child->IsPageContentFrame(), "unexpected child frame type");
auto* currentPageCF = static_cast<nsPageContentFrame*>(child);
if (StaticPrefs::layout_display_list_improve_fragmentation() &&
mPageNum <= 255) {
nsDisplayListBuilder::AutoPageNumberSetter p(aBuilder, mPageNum);
BuildPreviousPageOverflow(aBuilder, this, currentPageCF, set);
// Set the visible rect to scrollable overflow rect of the child
// nsPageContentFrame in parent nsPageFrame coordinate space.
const nsRect childOverflowRect =
const nsRect visibleRect = childOverflowRect + child->GetOffsetTo(this);
nsDisplayListBuilder::AutoBuildingDisplayList buildingForChild(
aBuilder, this, visibleRect, visibleRect);
BuildDisplayListForChild(aBuilder, child, set);
set.SerializeWithCorrectZOrder(&content, child->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.
NS_ASSERTION(mPageNum <= 255, "Too many pages to handle OOFs");
if (mPageNum <= 255) {
nsDisplayListBuilder::AutoPageNumberSetter p(aBuilder, mPageNum);
// 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 = currentPageCF;
while ((pageCF = static_cast<nsPageContentFrame*>(
pageCF->GetNextContinuation()))) {
nsRect childVisible = childOverflowRect + child->GetOffsetTo(pageCF);
nsDisplayListBuilder::AutoBuildingDisplayList buildingForChild(
aBuilder, pageCF, childVisible, childVisible);
BuildDisplayListForExtraPage(aBuilder, this, pageCF, &content);
// Invoke AutoBuildingDisplayList to ensure that the correct visibleRect
// is used to compute the visible rect if AddCanvasBackgroundColorItem
// creates a display item.
nsDisplayListBuilder::AutoBuildingDisplayList building(
aBuilder, child, childOverflowRect, childOverflowRect);
// 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.
nsRect backgroundRect =
nsRect(aBuilder->ToReferenceFrame(child), child->GetSize());
aBuilder, &content, child, backgroundRect, NS_RGBA(0, 0, 0, 0));
content.AppendNewToTop<nsDisplayTransform>(aBuilder, child, &content,
if (pc->IsRootPaginatedDocument()) {
content.AppendNewToTop<nsDisplayHeaderFooter>(aBuilder, this);
// For print-preview, show margin guides if requested in the settings.
if (pc->Type() == nsPresContext::eContext_PrintPreview &&
mPD->mPrintSettings->GetShowMarginGuides()) {
aBuilder, this, PaintMarginGuides, "MarginGuides",
void nsPageFrame::DeterminePageNum() {
// If we have no previous continuation, we're page 1. Otherwise, we're
// just one more than our previous continuation's page number.
auto* prevContinuation = static_cast<nsPageFrame*>(GetPrevContinuation());
mPageNum = prevContinuation ? prevContinuation->GetPageNum() + 1 : 1;
void nsPageFrame::PaintHeaderFooter(gfxContext& aRenderingContext, nsPoint aPt,
bool aDisableSubpixelAA) {
nsPresContext* pc = PresContext();
nsRect rect(aPt, mRect.Size());
DrawTargetAutoDisableSubpixelAntialiasing disable(
aRenderingContext.GetDrawTarget(), aDisableSubpixelAA);
// Get the FontMetrics to determine width.height of strings
nsFontMetrics::Params params;
params.userFontSet = pc->GetUserFontSet();
params.textPerf = pc->GetTextPerfMetrics();
params.fontStats = pc->GetFontMatchingStats();
params.featureValueLookup = pc->GetFontFeatureValuesLookup();
RefPtr<nsFontMetrics> fontMet =
pc->DeviceContext()->GetMetricsFor(mPD->mHeadFootFont, params);
nscoord ascent = fontMet->MaxAscent();
nscoord visibleHeight = fontMet->MaxHeight();
// print document headers and footers
nsString headerLeft, headerCenter, headerRight;
DrawHeaderFooter(aRenderingContext, *fontMet, eHeader, headerLeft,
headerCenter, headerRight, rect, ascent, visibleHeight);
nsString footerLeft, footerCenter, footerRight;
DrawHeaderFooter(aRenderingContext, *fontMet, eFooter, footerLeft,
footerCenter, footerRight, rect, ascent, visibleHeight);
void nsPageFrame::SetSharedPageData(nsSharedPageData* aPD) {
mPD = aPD;
// Set the shared data into the page frame before reflow
nsPageContentFrame* pcf =
if (pcf) {
nsIFrame* NS_NewPageBreakFrame(PresShell* aPresShell, ComputedStyle* aStyle) {
MOZ_ASSERT(aPresShell, "null PresShell");
// check that we are only creating page break frames when printing
"created a page break frame while not printing");
return new (aPresShell)
nsPageBreakFrame(aStyle, aPresShell->GetPresContext());
nsPageBreakFrame::nsPageBreakFrame(ComputedStyle* aStyle,
nsPresContext* aPresContext)
: nsLeafFrame(aStyle, aPresContext, kClassID), mHaveReflowed(false) {}
nsPageBreakFrame::~nsPageBreakFrame() = default;
nscoord nsPageBreakFrame::GetIntrinsicISize() {
return nsPresContext::CSSPixelsToAppUnits(1);
nscoord nsPageBreakFrame::GetIntrinsicBSize() { return 0; }
void nsPageBreakFrame::Reflow(nsPresContext* aPresContext,
ReflowOutput& aReflowOutput,
const ReflowInput& aReflowInput,
nsReflowStatus& aStatus) {
DISPLAY_REFLOW(aPresContext, this, aReflowInput, aReflowOutput, aStatus);
MOZ_ASSERT(aStatus.IsEmpty(), "Caller should pass a fresh reflow status!");
// Override reflow, since we don't want to deal with what our
// computed values are.
WritingMode wm = aReflowInput.GetWritingMode();
nscoord bSize = aReflowInput.AvailableBSize();
if (aReflowInput.AvailableBSize() == NS_UNCONSTRAINEDSIZE) {
bSize = nscoord(0);
} else if (GetContent()->IsHTMLElement(nsGkAtoms::legend)) {
// If this is a page break frame for a _rendered legend_ then it should be
// ignored since these frames are inserted inside the fieldset's inner
// frame and thus "misplaced". nsFieldSetFrame::Reflow deals with these
// forced breaks explicitly instead.
nsContainerFrame* parent = GetParent();
if (parent &&
parent->Style()->GetPseudoType() == PseudoStyleType::fieldsetContent) {
while ((parent = parent->GetParent())) {
if (nsFieldSetFrame* fieldset = do_QueryFrame(parent)) {
auto* legend = fieldset->GetLegend();
if (legend && legend->GetContent() == GetContent()) {
bSize = nscoord(0);
LogicalSize finalSize(wm, GetIntrinsicISize(), bSize);
// round the height down to the nearest pixel
// XXX(mats) why???
finalSize.BSize(wm) -=
finalSize.BSize(wm) % nsPresContext::CSSPixelsToAppUnits(1);
aReflowOutput.SetSize(wm, finalSize);
// Note: not using NS_FRAME_FIRST_REFLOW here, since it's not clear whether
// DidReflow will always get called before the next Reflow() call.
mHaveReflowed = true;
nsresult nsPageBreakFrame::GetFrameName(nsAString& aResult) const {
return MakeFrameName(u"PageBreak"_ns, aResult);