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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 */
/* Rendering object for a printed or print-previewed sheet of paper */
#include "mozilla/PrintedSheetFrame.h"
#include <tuple>
#include "mozilla/StaticPrefs_print.h"
#include "nsCSSFrameConstructor.h"
#include "nsPageContentFrame.h"
#include "nsPageFrame.h"
#include "nsPageSequenceFrame.h"
using namespace mozilla;
PrintedSheetFrame* NS_NewPrintedSheetFrame(PresShell* aPresShell,
ComputedStyle* aStyle) {
return new (aPresShell)
PrintedSheetFrame(aStyle, aPresShell->GetPresContext());
namespace mozilla {
void PrintedSheetFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
const nsDisplayListSet& aLists) {
if (PresContext()->IsScreen()) {
// Draw the background/shadow/etc. of a blank sheet of paper, for
// print-preview.
DisplayBorderBackgroundOutline(aBuilder, aLists);
for (auto* frame : mFrames) {
if (!frame->HasAnyStateBits(NS_PAGE_SKIPPED_BY_CUSTOM_RANGE)) {
BuildDisplayListForChild(aBuilder, frame, aLists);
// If the given page is included in the user's page range, this function
// returns false. Otherwise, it tags the page with the
// NS_PAGE_SKIPPED_BY_CUSTOM_RANGE state bit and returns true.
static bool TagIfSkippedByCustomRange(nsPageFrame* aPageFrame, int32_t aPageNum,
nsSharedPageData* aPD) {
if (!nsIPrintSettings::IsPageSkipped(aPageNum, aPD->mPageRanges)) {
"page frames NS_PAGE_SKIPPED_BY_CUSTOM_RANGE state should "
"only be set if we actually want to skip the page");
return false;
return true;
void PrintedSheetFrame::ClaimPageFrameFromPrevInFlow() {
if (!GetPrevContinuation()) {
// The first page content frame of each document will not yet have its page
// style set yet. This is because normally page style is set either from
// the previous page content frame, or using the new page name when named
// pages cause a page break in block reflow. Ensure that, for the first
// page, it is set here so that all nsPageContentFrames have their page
// style set before reflow.
auto* firstChild = PrincipalChildList().FirstChild();
MOZ_ASSERT(firstChild && firstChild->IsPageFrame(),
"PrintedSheetFrame only has nsPageFrame children");
auto* pageFrame = static_cast<nsPageFrame*>(firstChild);
void PrintedSheetFrame::Reflow(nsPresContext* aPresContext,
ReflowOutput& aReflowOutput,
const ReflowInput& aReflowInput,
nsReflowStatus& aStatus) {
MOZ_ASSERT(aStatus.IsEmpty(), "Caller should pass a fresh reflow status!");
// If we have a prev-in-flow, take its overflowing content:
const WritingMode wm = aReflowInput.GetWritingMode();
// See the comments for GetSizeForChildren.
// Note that nsPageFrame::ComputeSinglePPSPageSizeScale depends on this value
// and is currently called while reflowing a single nsPageFrame child (i.e.
// before we've finished reflowing ourself). Ideally our children wouldn't be
// accessing our dimensions until after we've finished reflowing ourself -
// see bug 1835782.
mSizeForChildren =
nsSize(aReflowInput.AvailableISize(), aReflowInput.AvailableBSize());
if (mPD->PagesPerSheetInfo()->mNumPages == 1) {
auto* firstChild = PrincipalChildList().FirstChild();
MOZ_ASSERT(firstChild && firstChild->IsPageFrame(),
"PrintedSheetFrame only has nsPageFrame children");
if (static_cast<nsPageFrame*>(firstChild)
->GetPageOrientationRotation(mPD) != 0.0) {
std::swap(mSizeForChildren.width, mSizeForChildren.height);
// Count the number of pages that are displayed on this sheet (i.e. how many
// child frames we end up laying out, excluding any pages that are skipped
// due to not being in the user's page-range selection).
uint32_t numPagesOnThisSheet = 0;
// Target for numPagesOnThisSheet.
const uint32_t desiredPagesPerSheet = mPD->PagesPerSheetInfo()->mNumPages;
if (desiredPagesPerSheet > 1) {
// NOTE: I'm intentionally *not* using a range-based 'for' loop here, since
// we potentially mutate the frame list (appending to the end) during the
// list, which is not generally safe with range-based 'for' loops.
for (auto* childFrame = mFrames.FirstChild(); childFrame;
childFrame = childFrame->GetNextSibling()) {
"we're only expecting page frames as children");
auto* pageFrame = static_cast<nsPageFrame*>(childFrame);
// Be sure our child has a pointer to the nsSharedPageData and knows its
// page number:
if (!TagIfSkippedByCustomRange(pageFrame, pageFrame->GetPageNum(), mPD)) {
// The page is going to be displayed on this sheet. Tell it its index
// among the displayed pages, so we can use that to compute its "cell"
// when painting.
// This is the app-unit size of the page (in physical & logical units).
// Note: The page sizes come from CSS or else from the user selected size;
// pages are never reflowed to fit their sheet - if/when necessary they are
// scaled to fit their sheet. Hence why we get the page's own dimensions to
// use as its "available space"/"container size" here.
const nsSize physPageSize = pageFrame->ComputePageSize();
const LogicalSize pageSize(wm, physPageSize);
ReflowInput pageReflowInput(aPresContext, aReflowInput, pageFrame,
// For layout purposes, we position *all* our nsPageFrame children at our
// origin. Then, if we have multiple pages-per-sheet, we'll shrink & shift
// each one into the right position as a paint-time effect, in
// BuildDisplayList.
LogicalPoint pagePos(wm);
// Outparams for reflow:
ReflowOutput pageReflowOutput(pageReflowInput);
nsReflowStatus status;
ReflowChild(pageFrame, aPresContext, pageReflowOutput, pageReflowInput, wm,
pagePos, physPageSize, ReflowChildFlags::Default, status);
FinishReflowChild(pageFrame, aPresContext, pageReflowOutput,
&pageReflowInput, wm, pagePos, physPageSize,
// Since we don't support incremental reflow in printed documents (see the
// early-return in nsPageSequenceFrame::Reflow), we can assume that this
// was the first time that pageFrame has been reflowed, and so there's no
// way that it could already have a next-in-flow. If it *did* have a
// next-in-flow, we would need to handle it in the 'status' logic below.
NS_ASSERTION(!pageFrame->GetNextInFlow(), "bad child flow list");
// Did this page complete the document, or do we need to generate
// another page frame?
if (status.IsFullyComplete()) {
// The page we just reflowed is the final page! Record its page number
// as the number of pages:
mPD->mRawNumPages = pageFrame->GetPageNum();
} else {
// Create a continuation for our page frame. We add the continuation to
// our child list, and then potentially push it to our overflow list, if
// it really belongs on the next sheet.
nsIFrame* continuingPage =
mFrames.InsertFrame(nullptr, pageFrame, continuingPage);
const bool isContinuingPageSkipped =
pageFrame->GetPageNum() + 1, mPD);
// If we've already reached the target number of pages for this sheet,
// and this continuation page that we just created is meant to be
// displayed (i.e. it's in the chosen page range), then we need to push it
// to our overflow list so that it'll go onto a subsequent sheet.
// Otherwise we leave it on this sheet. This ensures we *only* generate
// another sheet IFF there's a displayable page that will end up on it.
if (numPagesOnThisSheet >= desiredPagesPerSheet &&
!isContinuingPageSkipped) {
PushChildrenToOverflow(continuingPage, pageFrame);
// This should hold for the first sheet, because our UI should prevent the
// user from creating a 0-length page range; and it should hold for
// subsequent sheets because we should only create an additional sheet when
// we discover a displayable (i.e. non-skipped) page that we need to push
// to that new sheet.
// XXXdholbert In certain edge cases (e.g. after a page-orientation-flip that
// reduces the page count), it's possible for us to be given a page range
// that is *entirely out-of-bounds* (with "from" & "to" both being larger
// than our actual page-number count). This scenario produces a single
// PrintedSheetFrame with zero displayable pages on it, which is a weird
// state to be in. This is hopefully a scenario that the frontend code can
// detect and recover from (e.g. by clamping the range to our reported
// `rawNumPages`), but it can't do that until *after* we've completed this
// problematic reflow and can reported an up-to-date `rawNumPages` to the
// frontend. So: to give the frontend a chance to intervene and apply some
// correction/clamping to its print-range parameters, we soften this
// assertion *specifically for the first printed sheet*.
if (!GetPrevContinuation()) {
NS_WARNING_ASSERTION(numPagesOnThisSheet > 0,
"Shouldn't create a sheet with no displayable pages "
"on it");
} else {
MOZ_ASSERT(numPagesOnThisSheet > 0,
"Shouldn't create a sheet with no displayable pages on it");
MOZ_ASSERT(numPagesOnThisSheet <= desiredPagesPerSheet,
"Shouldn't have more than desired number of displayable pages "
"on this sheet");
mNumPages = numPagesOnThisSheet;
// Populate our ReflowOutput outparam -- just use up all the
// available space, for both our desired size & overflow areas.
aReflowOutput.ISize(wm) = aReflowInput.AvailableISize();
if (aReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE) {
aReflowOutput.BSize(wm) = aReflowInput.AvailableBSize();
nsSize PrintedSheetFrame::ComputeSheetSize(const nsPresContext* aPresContext) {
// We use the user selected page (sheet) dimensions, and default to the
// orientation as specified by the user.
nsSize sheetSize = aPresContext->GetPageSize();
// Don't waste cycles changing the orientation of a square.
if (sheetSize.width == sheetSize.height) {
return sheetSize;
if (!StaticPrefs::
print_save_as_pdf_use_page_rule_size_as_paper_size_enabled()) {
if (mPD->mPrintSettings->HasOrthogonalPagesPerSheet()) {
std::swap(sheetSize.width, sheetSize.height);
return sheetSize;
auto* firstChild = PrincipalChildList().FirstChild();
"PrintedSheetFrame only has nsPageFrame children");
auto* sheetsFirstPageFrame = static_cast<nsPageFrame*>(firstChild);
nsSize pageSize = sheetsFirstPageFrame->ComputePageSize();
// Don't waste cycles changing the orientation of a square.
if (pageSize.width == pageSize.height) {
return sheetSize;
const bool pageIsRotated =
sheetsFirstPageFrame->GetPageOrientationRotation(mPD) != 0.0;
if (pageIsRotated && pageSize.width == pageSize.height) {
// Straighforward rotation without needing sheet orientation optimization.
std::swap(sheetSize.width, sheetSize.height);
return sheetSize;
// Try to orient the sheet optimally based on the physical orientation of the
// first/sole page on the sheet. (In the multiple pages-per-sheet case, the
// first page is the only one that exists at this point in the code, so it is
// the only one we can reason about. Any other pages may, or may not, have
// the same physical orientation.)
if (pageIsRotated) {
// Fix up for its physical orientation:
std::swap(pageSize.width, pageSize.height);
const bool pageIsPortrait = pageSize.width < pageSize.height;
const bool sheetIsPortrait = sheetSize.width < sheetSize.height;
// Switch the sheet orientation if the page orientation is different, or
// if we need to switch it because the number of pages-per-sheet demands
// orthogonal sheet layout, but not if both are true since then we'd
// actually need to double switch.
if ((sheetIsPortrait != pageIsPortrait) !=
mPD->mPrintSettings->HasOrthogonalPagesPerSheet()) {
std::swap(sheetSize.width, sheetSize.height);
return sheetSize;
void PrintedSheetFrame::ComputePagesPerSheetGridMetrics(
const nsSize& aSheetSize) {
MOZ_ASSERT(mPD->PagesPerSheetInfo()->mNumPages > 1,
"Unnecessary to call this in a regular 1-page-per-sheet scenario; "
"the computed values won't ever be used in that case");
// Compute the space available for the pages-per-sheet "page grid" (just
// subtract the sheet's unwriteable margin area):
nsSize availSpaceOnSheet = aSheetSize;
nsMargin uwm = mPD->mPrintSettings->GetIgnoreUnwriteableMargins()
? nsMargin{}
: nsPresContext::CSSTwipsToAppUnits(
// XXXjwatt Once we support heterogeneous sheet orientations, we'll also need
// to rotate uwm if this sheet is not the primary orientation.
if (mPD->mPrintSettings->HasOrthogonalPagesPerSheet()) {
// aSheetSize already takes account of the switch of *sheet* orientation
// that we do in this case (the orientation implied by the page size
// dimensions in the nsIPrintSettings applies to *pages*). That is not the
// case for the unwriteable margins since we got them from the
// nsIPrintSettings object ourself, so we need to adjust `uwm` here.
// Note: In practice, sheets with an orientation that is orthogonal to the
// physical orientation of sheets output by a printer must be rotated 90
// degrees for/by the printer. In that case the convention seems to be that
// the "left" edge of the orthogonally oriented sheet becomes the "top",
// and so forth. The rotation direction will matter in the case that the
// top and bottom unwriteable margins are different, or the left and right
// unwriteable margins are different. So we need to match this behavior,
// which means we must rotate the `uwm` 90 degrees *counter-clockwise*.
nsMargin rotated(uwm.right, uwm.bottom, uwm.left,;
uwm = rotated;
availSpaceOnSheet.width -= uwm.LeftRight();
availSpaceOnSheet.height -= uwm.TopBottom();
if (MOZ_UNLIKELY(availSpaceOnSheet.IsEmpty())) {
// This sort of thing should be rare, but it can happen if there are
// bizarre page sizes, and/or if there's an unexpectedly large unwriteable
// margin area.
NS_WARNING("Zero area for pages-per-sheet grid, or zero-sized grid");
mGridOrigin = nsPoint(0, 0);
mGridNumCols = 1;
// If there are a different number of rows vs. cols, we'll aim to put
// the larger number of items in the longer axis.
const auto* ppsInfo = mPD->PagesPerSheetInfo();
uint32_t smallerNumTracks = ppsInfo->mNumPages / ppsInfo->mLargerNumTracks;
bool sheetIsPortraitLike = aSheetSize.width < aSheetSize.height;
auto numCols =
sheetIsPortraitLike ? smallerNumTracks : ppsInfo->mLargerNumTracks;
auto numRows =
sheetIsPortraitLike ? ppsInfo->mLargerNumTracks : smallerNumTracks;
mGridOrigin = nsPoint(uwm.left,;
mGridNumCols = numCols;
mGridCellWidth = availSpaceOnSheet.width / nscoord(numCols);
mGridCellHeight = availSpaceOnSheet.height / nscoord(numRows);
gfx::IntSize PrintedSheetFrame::GetPrintTargetSizeInPoints(
const int32_t aAppUnitsPerPhysicalInch) const {
const auto size = GetSize();
MOZ_ASSERT(size.width > 0 && size.height > 0);
const float pointsPerAppUnit =
POINTS_PER_INCH_FLOAT / float(aAppUnitsPerPhysicalInch);
return IntSize::Ceil(float(size.width) * pointsPerAppUnit,
float(size.height) * pointsPerAppUnit);
nsresult PrintedSheetFrame::GetFrameName(nsAString& aResult) const {
return MakeFrameName(u"PrintedSheet"_ns, aResult);
} // namespace mozilla