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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 "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::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!");
// If we have a prev-in-flow, take its overflowing content:
const WritingMode wm = aReflowInput.GetWritingMode();
// This is the app-unit size of each page (in physical & logical units):
const nsSize physPageSize = aPresContext->GetPageSize();
const LogicalSize pageSize(wm, physPageSize);
// 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 we're the first continuation and we're doing >1 pages per sheet,
// precompute some metrics that we'll use when painting the pages:
if (desiredPagesPerSheet > 1 && !GetPrevContinuation()) {
// 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.
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();
void PrintedSheetFrame::ComputePagesPerSheetOriginAndScale() {
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");
"Only needs to be called once, so 1st continuation handles it");
// The "full-scale" size of a page (if it weren't shrunk down into a grid):
const nsSize pageSize = PresContext()->GetPageSize();
// Compute the space available for the pages-per-sheet "page grid" (just
// subtract the sheet's unwriteable margin area):
nsSize availSpaceOnSheet = pageSize;
nsMargin uwm = mPD->mPrintSettings->GetIgnoreUnwriteableMargins()
? nsMargin{}
: nsPresContext::CSSTwipsToAppUnits(
if (mPD->mPrintSettings->HasOrthogonalSheetsAndPages()) {
// The pages will be rotated to be orthogonal to the physical sheet. To
// account for that, we rotate the components of availSpaceOnSheet and uwm,
// so that we can reason about them here from the perspective of a
// "pageSize"-oriented *page*.
std::swap(availSpaceOnSheet.width, availSpaceOnSheet.height);
// Note that the pages are rotated 90 degrees clockwise when placed onto a
// sheet (so that, e.g. in a scenario with two side-by-side portait pages
// that are rotated & placed onto a sheet, the "left" edge of the first
// page is at the "top" of the sheet and hence comes out of the printer
// first, etc). So: given `nsMargin uwm` whose sides correspond to the
// physical sheet's sides, we have to rotate 90 degrees *counter-clockwise*
// in order to "cancel out" the page rotation and to represent it in the
// page's perspective. From a page's perspective, its own "top" side
// corresponds to the physical sheet's right side, which is why we're
// passing "uwm.right" as the "top" component here; and so on.
nsMargin rotated(uwm.right, uwm.bottom, uwm.left,;
uwm = rotated;
availSpaceOnSheet.width -= uwm.LeftRight();
availSpaceOnSheet.height -= uwm.TopBottom();
nsPoint pageGridOrigin(uwm.left,;
// 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 pageSizeIsPortraitLike = pageSize.width > pageSize.height;
auto numCols =
pageSizeIsPortraitLike ? smallerNumTracks : ppsInfo->mLargerNumTracks;
auto numRows =
pageSizeIsPortraitLike ? ppsInfo->mLargerNumTracks : smallerNumTracks;
// Compute the full size of the "page grid" that we'll be scaling down &
// placing onto a given sheet:
nsSize pageGridFullSize(numCols * pageSize.width, numRows * pageSize.height);
if (MOZ_UNLIKELY(availSpaceOnSheet.IsEmpty() || pageGridFullSize.IsEmpty())) {
// Either we have a 0-sized available area, or we have a 0-sized page-grid
// to draw into the available area. 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 unwritable margin area. Regardless: if we get here,
// we shouldn't be drawing anything onto the sheet; so let's just use a
// scale factor of 0, and bail early to avoid division by 0 in hScale &
// vScale computations below.
NS_WARNING("Zero area for pages-per-sheet grid, or zero-sized grid");
mPD->mPagesPerSheetGridOrigin = pageGridOrigin;
mPD->mPagesPerSheetNumCols = 1;
mPD->mPagesPerSheetScale = 0.0f;
// Compute the scale factors required in each axis:
float hScale =
availSpaceOnSheet.width / static_cast<float>(pageGridFullSize.width);
float vScale =
availSpaceOnSheet.height / static_cast<float>(pageGridFullSize.height);
// Choose the more restrictive scale factor (so that we don't overflow the
// sheet's printable area in either axis). And center the page-grid in the
// other axis (since it probably ends up with extra space).
float scale = std::min(hScale, vScale);
if (hScale < vScale) {
// hScale is the more restrictive scale-factor, so we'll be using that.
// Nudge the grid in the vertical axis to center it:
nscoord extraSpace = availSpaceOnSheet.height -
NSToCoordFloor(scale * pageGridFullSize.height);
if (MOZ_LIKELY(extraSpace > 0)) {
pageGridOrigin.y += extraSpace / 2;
} else if (vScale < hScale) {
// vScale is the more restrictive scale-factor, so we'll be using that.
// Nudge the grid in the vertical axis to center it:
nscoord extraSpace = availSpaceOnSheet.width -
NSToCoordFloor(scale * pageGridFullSize.width);
if (MOZ_LIKELY(extraSpace > 0)) {
pageGridOrigin.x += extraSpace / 2;
// else, we fit exactly in both axes, with the same scale factor, so there's
// no extra space in either axis, i.e. no need to center.
// Update the nsSharedPageData member data:
mPD->mPagesPerSheetGridOrigin = pageGridOrigin;
mPD->mPagesPerSheetNumCols = numCols;
mPD->mPagesPerSheetScale = scale;
nsresult PrintedSheetFrame::GetFrameName(nsAString& aResult) const {
return MakeFrameName(u"PrintedSheet"_ns, aResult);
} // namespace mozilla