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/* 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 "Units.h"
#include "mozilla/PresShell.h"
#include "mozilla/ViewportFrame.h"
#include "mozilla/ViewportUtils.h"
#include "mozilla/dom/BrowserChild.h"
#include "mozilla/layers/APZCCallbackHelper.h"
#include "mozilla/layers/InputAPZContext.h"
#include "mozilla/layers/ScrollableLayerGuid.h"
#include "nsIContent.h"
#include "nsIFrame.h"
#include "nsIScrollableFrame.h"
#include "nsLayoutUtils.h"
#include "nsQueryFrame.h"
#include "nsStyleStruct.h"
namespace mozilla {
using layers::APZCCallbackHelper;
using layers::InputAPZContext;
using layers::ScrollableLayerGuid;
template <typename Units>
gfx::Matrix4x4Typed<Units, Units> ViewportUtils::GetVisualToLayoutTransform(
ScrollableLayerGuid::ViewID aScrollId) {
std::is_same_v<Units, CSSPixel> ||
std::is_same_v<Units, LayoutDevicePixel>,
"GetCallbackTransform() may only be used with CSS or LayoutDevice units");
if (aScrollId == ScrollableLayerGuid::NULL_SCROLL_ID) {
return {};
nsCOMPtr<nsIContent> content = nsLayoutUtils::FindContentFor(aScrollId);
if (!content || !content->GetPrimaryFrame()) {
return {};
// First, scale inversely by the root content document's pres shell
// resolution to cancel the scale-to-resolution transform that the
// compositor adds to the layer with the pres shell resolution. The points
// sent to Gecko by APZ don't have this transform unapplied (unlike other
// compositor-side transforms) because Gecko needs it applied when hit
// testing against content that's conceptually outside the resolution,
// such as scrollbars.
float resolution = 1.0f;
if (PresShell* presShell =
content)) {
resolution = presShell->GetResolution();
// Now apply the callback-transform. This is only approximately correct,
// see the comment on GetCumulativeApzCallbackTransform for details.
gfx::PointTyped<Units> transform;
CSSPoint transformCSS = nsLayoutUtils::GetCumulativeApzCallbackTransform(
if constexpr (std::is_same_v<Units, CSSPixel>) {
transform = transformCSS;
} else { // Units == LayoutDevicePixel
transform = transformCSS *
return gfx::Matrix4x4Typed<Units, Units>::Scaling(1 / resolution,
1 / resolution, 1)
.PostTranslate(transform.x, transform.y, 0);
CSSToCSSMatrix4x4 GetVisualToLayoutTransform(PresShell* aContext) {
ScrollableLayerGuid::ViewID targetScrollId =
if (targetScrollId == ScrollableLayerGuid::NULL_SCROLL_ID) {
if (nsIFrame* rootScrollFrame = aContext->GetRootScrollFrame()) {
targetScrollId =
return ViewportUtils::GetVisualToLayoutTransform(targetScrollId);
nsPoint ViewportUtils::VisualToLayout(const nsPoint& aPt, PresShell* aContext) {
auto visualToLayout = mozilla::GetVisualToLayoutTransform(aContext);
CSSPoint cssPt = CSSPoint::FromAppUnits(aPt);
cssPt = visualToLayout.TransformPoint(cssPt);
return CSSPoint::ToAppUnits(cssPt);
nsRect ViewportUtils::VisualToLayout(const nsRect& aRect, PresShell* aContext) {
auto visualToLayout = mozilla::GetVisualToLayoutTransform(aContext);
CSSRect cssRect = CSSRect::FromAppUnits(aRect);
cssRect = visualToLayout.TransformBounds(cssRect);
nsRect result = CSSRect::ToAppUnits(cssRect);
// In hit testing codepaths, the input rect often has dimensions of one app
// units. If we are zoomed in enough, the rounded size of the output rect
// can be zero app units, which will fail to Intersect() with anything, and
// therefore cause hit testing to fail. To avoid this, we expand the output
// rect to one app units.
if (!aRect.IsEmpty() && result.IsEmpty()) {
result.width = 1;
result.height = 1;
return result;
nsPoint ViewportUtils::LayoutToVisual(const nsPoint& aPt, PresShell* aContext) {
auto visualToLayout = mozilla::GetVisualToLayoutTransform(aContext);
CSSPoint cssPt = CSSPoint::FromAppUnits(aPt);
auto transformed = visualToLayout.Inverse().TransformPoint(cssPt);
return CSSPoint::ToAppUnits(transformed);
LayoutDevicePoint ViewportUtils::DocumentRelativeLayoutToVisual(
const LayoutDevicePoint& aPoint, PresShell* aShell) {
ScrollableLayerGuid::ViewID targetScrollId =
auto visualToLayout =
return visualToLayout.Inverse().TransformPoint(aPoint);
LayoutDeviceRect ViewportUtils::DocumentRelativeLayoutToVisual(
const LayoutDeviceRect& aRect, PresShell* aShell) {
ScrollableLayerGuid::ViewID targetScrollId =
auto visualToLayout =
return visualToLayout.Inverse().TransformBounds(aRect);
LayoutDeviceRect ViewportUtils::DocumentRelativeLayoutToVisual(
const LayoutDeviceIntRect& aRect, PresShell* aShell) {
return DocumentRelativeLayoutToVisual(IntRectToRect(aRect), aShell);
CSSRect ViewportUtils::DocumentRelativeLayoutToVisual(const CSSRect& aRect,
PresShell* aShell) {
ScrollableLayerGuid::ViewID targetScrollId =
auto visualToLayout =
return visualToLayout.Inverse().TransformBounds(aRect);
template <class SourceUnits, class DestUnits>
gfx::PointTyped<DestUnits> TransformPointOrRect(
const gfx::Matrix4x4Typed<SourceUnits, DestUnits>& aMatrix,
const gfx::PointTyped<SourceUnits>& aPoint) {
return aMatrix.TransformPoint(aPoint);
template <class SourceUnits, class DestUnits>
gfx::RectTyped<DestUnits> TransformPointOrRect(
const gfx::Matrix4x4Typed<SourceUnits, DestUnits>& aMatrix,
const gfx::RectTyped<SourceUnits>& aRect) {
return aMatrix.TransformBounds(aRect);
template <class LDPointOrRect>
LDPointOrRect ConvertToScreenRelativeVisual(const LDPointOrRect& aInput,
nsPresContext* aCtx) {
LDPointOrRect layoutToVisual(aInput);
nsIFrame* prevRootFrame = nullptr;
nsPresContext* prevCtx = nullptr;
// Walk up to the rootmost prescontext, transforming as we go.
for (nsPresContext* ctx = aCtx; ctx; ctx = ctx->GetParentPresContext()) {
PresShell* shell = ctx->PresShell();
nsIFrame* rootFrame = shell->GetRootFrame();
if (prevRootFrame) {
// Convert layoutToVisual from being relative to `prevRootFrame`
// to being relative to `rootFrame` (layout space).
nscoord apd = prevCtx->AppUnitsPerDevPixel();
nsPoint offset = prevRootFrame->GetOffsetToCrossDoc(rootFrame, apd);
layoutToVisual += LayoutDevicePoint::FromAppUnits(offset, apd);
if (shell->GetResolution() != 1.0) {
// Found the APZ zoom root, so do the layout -> visual conversion.
layoutToVisual =
ViewportUtils::DocumentRelativeLayoutToVisual(layoutToVisual, shell);
prevRootFrame = rootFrame;
prevCtx = ctx;
// If we're in a nested content process, the above traversal will not have
// encountered the APZ zoom root. The translation part of the layout-to-visual
// transform will be included in |rootScreenRect.TopLeft()|, added below
// (that ultimately comes from nsIWidget::WidgetToScreenOffset(), which for an
// OOP iframe's widget includes this translation), but the scale part needs to
// be computed and added separately.
Scale2D enclosingResolution =
if (enclosingResolution != Scale2D{1.0f, 1.0f}) {
layoutToVisual = TransformPointOrRect(
enclosingResolution.xScale, enclosingResolution.yScale, 1.0f),
// Then we do the conversion from the rootmost presContext's root frame (in
// visual space) to screen space.
LayoutDeviceIntRect rootScreenRect =
return layoutToVisual + rootScreenRect.TopLeft();
LayoutDevicePoint ViewportUtils::ToScreenRelativeVisual(
const LayoutDevicePoint& aPt, nsPresContext* aCtx) {
return ConvertToScreenRelativeVisual(aPt, aCtx);
LayoutDeviceRect ViewportUtils::ToScreenRelativeVisual(
const LayoutDeviceRect& aRect, nsPresContext* aCtx) {
return ConvertToScreenRelativeVisual(aRect, aCtx);
// Definitions of the two explicit instantiations forward declared in the header
// file. This causes code for these instantiations to be emitted into the object
// file for ViewportUtils.cpp.
template CSSToCSSMatrix4x4 ViewportUtils::GetVisualToLayoutTransform<CSSPixel>(
template LayoutDeviceToLayoutDeviceMatrix4x4
const nsIFrame* ViewportUtils::IsZoomedContentRoot(const nsIFrame* aFrame) {
if (!aFrame) {
return nullptr;
if (aFrame->Type() == LayoutFrameType::Canvas ||
aFrame->Type() == LayoutFrameType::PageSequence) {
nsIScrollableFrame* sf = do_QueryFrame(aFrame->GetParent());
if (sf && sf->IsRootScrollFrameOfDocument() &&
aFrame->PresContext()->IsRootContentDocumentCrossProcess()) {
return aFrame->GetParent();
} else if (aFrame->StyleDisplay()->mPosition ==
StylePositionProperty::Fixed) {
if (ViewportFrame* viewportFrame = do_QueryFrame(aFrame->GetParent())) {
if (viewportFrame->PresContext()->IsRootContentDocumentCrossProcess()) {
return viewportFrame->PresShell()->GetRootScrollFrame();
return nullptr;
Scale2D ViewportUtils::TryInferEnclosingResolution(PresShell* aShell) {
MOZ_ASSERT(aShell && aShell->GetPresContext());
"TryInferEnclosingResolution can only be called for a root pres "
"shell within a process");
if (dom::BrowserChild* bc = dom::BrowserChild::GetFrom(aShell)) {
if (!bc->IsTopLevel()) {
// The enclosing resolution is not directly available in the BrowserChild.
// The closest thing available is GetChildToParentConversionMatrix(),
// which also includes any enclosing CSS transforms.
// The behaviour implemented here will not provide an accurate answer
// in the presence of CSS transforms, but it tries to do something
// reasonable:
// - If there are no enclosing CSS transforms, it will return the
// resolution.
// - If the enclosing transforms contain scales and translations only,
// it will return the resolution times the CSS transform scale
// (choosing the x-scale if they are different).
// - Otherwise, it will return the resolution times a scale component
// of the transform as returned by Matrix4x4Typed::Decompose().
// - If the enclosing transform is sufficiently complex that
// Decompose() returns false, give up and return 1.0.
gfx::Point3DTyped<gfx::UnknownUnits> translation;
gfx::Quaternion rotation;
gfx::Point3DTyped<gfx::UnknownUnits> scale;
if (bc->GetChildToParentConversionMatrix().Decompose(translation,
rotation, scale)) {
return {scale.x, scale.y};
return {1.0f, 1.0f};
} // namespace mozilla