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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 "DoubleTapToZoom.h"
#include <algorithm> // for std::min, std::max
#include "mozilla/PresShell.h"
#include "mozilla/AlreadyAddRefed.h"
#include "mozilla/dom/Element.h"
#include "mozilla/dom/EffectsInfo.h"
#include "mozilla/dom/BrowserChild.h"
#include "nsCOMPtr.h"
#include "nsIContent.h"
#include "mozilla/dom/Document.h"
#include "nsIFrame.h"
#include "nsIFrameInlines.h"
#include "nsIScrollableFrame.h"
#include "nsTableCellFrame.h"
#include "nsLayoutUtils.h"
#include "nsStyleConsts.h"
#include "mozilla/ViewportUtils.h"
#include "mozilla/EventListenerManager.h"
#include "mozilla/layers/APZUtils.h"
namespace mozilla {
namespace layers {
namespace {
using FrameForPointOption = nsLayoutUtils::FrameForPointOption;
static bool IsGeneratedContent(nsIContent* aContent) {
// We exclude marks because making them double tap targets does not seem
// desirable.
return aContent->IsGeneratedContentContainerForBefore() ||
// Returns the DOM element found at |aPoint|, interpreted as being relative to
// the root frame of |aPresShell| in visual coordinates. If the point is inside
// a subdocument, returns an element inside the subdocument, rather than the
// subdocument element (and does so recursively). The implementation was adapted
// from DocumentOrShadowRoot::ElementFromPoint(), with the notable exception
// that we don't pass nsLayoutUtils::IGNORE_CROSS_DOC to GetFrameForPoint(), so
// as to get the behaviour described above in the presence of subdocuments.
static already_AddRefed<dom::Element> ElementFromPoint(
const RefPtr<PresShell>& aPresShell, const CSSPoint& aPoint) {
nsIFrame* rootFrame = aPresShell->GetRootFrame();
if (!rootFrame) {
return nullptr;
nsIFrame* frame = nsLayoutUtils::GetFrameForPoint(
RelativeTo{rootFrame, ViewportType::Visual}, CSSPoint::ToAppUnits(aPoint),
while (frame && (!frame->GetContent() ||
(frame->GetContent()->IsInNativeAnonymousSubtree() &&
!IsGeneratedContent(frame->GetContent())))) {
frame = nsLayoutUtils::GetParentOrPlaceholderFor(frame);
if (!frame) {
return nullptr;
// FIXME(emilio): This should probably use the flattened tree, GetParent() is
// not guaranteed to be an element in presence of shadow DOM.
nsIContent* content = frame->GetContent();
if (!content) {
return nullptr;
if (dom::Element* element = content->GetAsElementOrParentElement()) {
return do_AddRef(element);
return nullptr;
// Get table cell from element, parent or grand parent.
static dom::Element* GetNearbyTableCell(
const nsCOMPtr<dom::Element>& aElement) {
nsTableCellFrame* tableCell = do_QueryFrame(aElement->GetPrimaryFrame());
if (tableCell) {
return aElement.get();
if (dom::Element* parent = aElement->GetFlattenedTreeParentElement()) {
nsTableCellFrame* tableCell = do_QueryFrame(parent->GetPrimaryFrame());
if (tableCell) {
return parent;
if (dom::Element* grandParent = parent->GetFlattenedTreeParentElement()) {
tableCell = do_QueryFrame(grandParent->GetPrimaryFrame());
if (tableCell) {
return grandParent;
return nullptr;
// A utility function returns the given |aElement| rectangle relative to the top
// level content document coordinates.
static CSSRect GetBoundingContentRect(
const dom::Element* aElement,
const RefPtr<dom::Document>& aInProcessRootContentDocument,
const nsIScrollableFrame* aRootScrollFrame,
const DoubleTapToZoomMetrics& aMetrics,
mozilla::Maybe<CSSRect>* aOutNearestScrollClip = nullptr) {
CSSRect result = nsLayoutUtils::GetBoundingContentRect(
aElement, aRootScrollFrame, aOutNearestScrollClip);
if (aInProcessRootContentDocument->IsTopLevelContentDocument()) {
return result;
nsIFrame* frame = aElement->GetPrimaryFrame();
if (!frame) {
return CSSRect();
// If the nearest scroll frame is |aRootScrollFrame|,
// nsLayoutUtils::GetBoundingContentRect doesn't set |aOutNearestScrollClip|,
// thus in the cases of OOP iframs, we need to use the visible rect of the
// iframe as the nearest scroll clip.
if (aOutNearestScrollClip && aOutNearestScrollClip->isNothing()) {
if (dom::BrowserChild* browserChild =
dom::BrowserChild::GetFrom(frame->PresShell())) {
const dom::EffectsInfo& effectsInfo = browserChild->GetEffectsInfo();
if (effectsInfo.IsVisible()) {
*aOutNearestScrollClip =[&aMetrics](const nsRect& aRect) {
return aMetrics.mTransformMatrix.TransformBounds(
// In the case of an element inside an OOP iframe, |aMetrics.mTransformMatrix|
// includes the translation information about the root layout scroll offset,
// thus we use nsIFrame::GetBoundingClientRect rather than
// nsLayoutUtils::GetBoundingContent.
return aMetrics.mTransformMatrix.TransformBounds(
static bool ShouldZoomToElement(
const nsCOMPtr<dom::Element>& aElement,
const RefPtr<dom::Document>& aInProcessRootContentDocument,
nsIScrollableFrame* aRootScrollFrame,
const DoubleTapToZoomMetrics& aMetrics) {
if (nsIFrame* frame = aElement->GetPrimaryFrame()) {
if (frame->StyleDisplay()->IsInlineFlow() &&
// Replaced elements are suitable zoom targets because they act like
// inline-blocks instead of inline. (textarea's are the specific reason
// we do this)
!frame->IsReplaced()) {
return false;
// Trying to zoom to the html element will just end up scrolling to the start
// of the document, return false and we'll run out of elements and just
// zoomout (without scrolling to the start).
if (aElement->OwnerDoc() == aInProcessRootContentDocument &&
aElement->IsHTMLElement(nsGkAtoms::html)) {
return false;
if (aElement->IsAnyOfHTMLElements(nsGkAtoms::li, nsGkAtoms::q)) {
return false;
// Ignore elements who are table cells or their parents are table cells, and
// they take up less than 30% of page rect width because they are likely cells
// in data tables (as opposed to tables used for layout purposes), and we
// don't want to zoom to them. This heuristic is quite naive and leaves a lot
// to be desired.
if (dom::Element* tableCell = GetNearbyTableCell(aElement)) {
CSSRect rect = GetBoundingContentRect(
tableCell, aInProcessRootContentDocument, aRootScrollFrame, aMetrics);
if (rect.width < 0.3 * aMetrics.mRootScrollableRect.width) {
return false;
return true;
// Calculates if zooming to aRect would have almost the same zoom level as
// aCompositedArea currently has. If so we would want to zoom out instead.
static bool RectHasAlmostSameZoomLevel(const CSSRect& aRect,
const CSSRect& aCompositedArea) {
// This functions checks to see if the area of the rect visible in the
// composition bounds (i.e. the overlapArea variable below) is approximately
// the max area of the rect we can show.
// AsyncPanZoomController::ZoomToRect will adjust the zoom and scroll offset
// so that the zoom to rect fills the composited area. If after adjusting the
// scroll offset _only_ the rect would fill the composited area we want to
// zoom out (we don't want to _just_ scroll, we want to do some amount of
// zooming, either in or out it doesn't matter which). So translate both rects
// to the same origin and then compute their overlap, which is what the
// following calculation does.
float overlapArea = std::min(aRect.width, aCompositedArea.width) *
std::min(aRect.height, aCompositedArea.height);
float availHeight = std::min(
aRect.Width() * aCompositedArea.Height() / aCompositedArea.Width(),
float showing = overlapArea / (aRect.Width() * availHeight);
float ratioW = aRect.Width() / aCompositedArea.Width();
float ratioH = aRect.Height() / aCompositedArea.Height();
return showing > 0.9 && (ratioW > 0.9 || ratioH > 0.9);
} // namespace
static CSSRect AddHMargin(const CSSRect& aRect, const CSSCoord& aMargin,
const CSSRect& aRootScrollableRect) {
CSSRect rect =
CSSRect(std::max(aRootScrollableRect.X(), aRect.X() - aMargin), aRect.Y(),
aRect.Width() + 2 * aMargin, aRect.Height());
// Constrict the rect to the screen's right edge
rect.SetWidth(std::min(rect.Width(), aRootScrollableRect.XMost() - rect.X()));
return rect;
static CSSRect AddVMargin(const CSSRect& aRect, const CSSCoord& aMargin,
const CSSRect& aRootScrollableRect) {
CSSRect rect =
CSSRect(aRect.X(), std::max(aRootScrollableRect.Y(), aRect.Y() - aMargin),
aRect.Width(), aRect.Height() + 2 * aMargin);
// Constrict the rect to the screen's bottom edge
std::min(rect.Height(), aRootScrollableRect.YMost() - rect.Y()));
return rect;
static bool IsReplacedElement(const nsCOMPtr<dom::Element>& aElement) {
if (nsIFrame* frame = aElement->GetPrimaryFrame()) {
if (frame->IsReplaced()) {
return true;
return false;
static bool HasNonPassiveWheelListenerOnAncestor(nsIContent* aContent) {
for (nsIContent* content = aContent; content;
content = content->GetFlattenedTreeParent()) {
EventListenerManager* elm = content->GetExistingListenerManager();
if (elm && elm->HasNonPassiveWheelListener()) {
return true;
return false;
ZoomTarget CalculateRectToZoomTo(
const RefPtr<dom::Document>& aInProcessRootContentDocument,
const CSSPoint& aPoint, const DoubleTapToZoomMetrics& aMetrics) {
// Ensure the layout information we get is up-to-date.
// An empty rect as return value is interpreted as "zoom out".
const CSSRect zoomOut;
RefPtr<PresShell> presShell = aInProcessRootContentDocument->GetPresShell();
if (!presShell) {
return ZoomTarget{zoomOut, CantZoomOutBehavior::ZoomIn};
nsIScrollableFrame* rootScrollFrame =
if (!rootScrollFrame) {
return ZoomTarget{zoomOut, CantZoomOutBehavior::ZoomIn};
CSSPoint documentRelativePoint =
? CSSPoint::FromAppUnits(ViewportUtils::VisualToLayout(
CSSPoint::ToAppUnits(aPoint), presShell)) +
: aMetrics.mTransformMatrix.TransformPoint(aPoint);
nsCOMPtr<dom::Element> element = ElementFromPoint(presShell, aPoint);
if (!element) {
return ZoomTarget{zoomOut, CantZoomOutBehavior::ZoomIn, Nothing(),
CantZoomOutBehavior cantZoomOutBehavior =
? CantZoomOutBehavior::Nothing
: CantZoomOutBehavior::ZoomIn;
while (element && !ShouldZoomToElement(element, aInProcessRootContentDocument,
rootScrollFrame, aMetrics)) {
element = element->GetFlattenedTreeParentElement();
if (!element) {
return ZoomTarget{zoomOut, cantZoomOutBehavior, Nothing(),
Maybe<CSSRect> nearestScrollClip;
CSSRect rect =
GetBoundingContentRect(element, aInProcessRootContentDocument,
rootScrollFrame, aMetrics, &nearestScrollClip);
// In some cases, like overflow: visible and overflowing content, the bounding
// client rect of the targeted element won't contain the point the user double
// tapped on. In that case we use the scrollable overflow rect if it contains
// the user point.
if (!rect.Contains(documentRelativePoint)) {
if (nsIFrame* scrolledFrame = rootScrollFrame->GetScrolledFrame()) {
if (nsIFrame* f = element->GetPrimaryFrame()) {
nsRect overflowRect = f->ScrollableOverflowRect();
nsLayoutUtils::TransformResult res =
nsLayoutUtils::TransformRect(f, scrolledFrame, overflowRect);
if (res == nsLayoutUtils::TRANSFORM_SUCCEEDED) {
CSSRect overflowRectCSS = CSSRect::FromAppUnits(overflowRect);
// In the case of OOP iframes, above |overflowRectCSS| in the iframe
// documents coords, we need to convert it into the top level coords.
if (!aInProcessRootContentDocument->IsTopLevelContentDocument()) {
overflowRectCSS =
if (nearestScrollClip.isSome()) {
overflowRectCSS = nearestScrollClip->Intersect(overflowRectCSS);
if (overflowRectCSS.Contains(documentRelativePoint)) {
rect = overflowRectCSS;
CSSRect elementBoundingRect = rect;
// Generally we zoom to the width of some element, but sometimes we zoom to
// the height. We set this to true when that happens so that we can add a
// vertical margin to the rect, otherwise it looks weird.
bool heightConstrained = false;
// If the element is taller than the visible area of the page scale
// the height of the |rect| so that it has the same aspect ratio as
// the root frame. The clipped |rect| is centered on the y value of
// the touch point. This allows tall narrow elements to be zoomed.
if (!rect.IsEmpty() && aMetrics.mVisualViewport.Width() > 0.0f &&
aMetrics.mVisualViewport.Height() > 0.0f) {
// Calculate the height of the rect if it had the same aspect ratio as
// aMetrics.mVisualViewport.
const float widthRatio = rect.Width() / aMetrics.mVisualViewport.Width();
float targetHeight = aMetrics.mVisualViewport.Height() * widthRatio;
// We don't want to cut off the top or bottoms of replaced elements that are
// square or wider in aspect ratio.
// If it's a replaced element and we would otherwise trim it's height below
if (IsReplacedElement(element) && targetHeight < rect.Height() &&
// If the target rect is at most 1.1x away from being square or wider
// aspect ratio
rect.Height() < 1.1 * rect.Width() &&
// and our aMetrics.mVisualViewport is wider than it is tall
aMetrics.mVisualViewport.Width() >= aMetrics.mVisualViewport.Height()) {
heightConstrained = true;
// Expand the width of the rect so that it fills aMetrics.mVisualViewport
// so that if we are already zoomed to this element then the
// IsRectZoomedIn call below returns true so that we zoom out. This won't
// change what we actually zoom to as we are just making the rect the same
// aspect ratio as aMetrics.mVisualViewport.
float targetWidth = rect.Height() * aMetrics.mVisualViewport.Width() /
MOZ_ASSERT(targetWidth > rect.Width());
if (targetWidth > rect.Width()) {
rect.x -= (targetWidth - rect.Width()) / 2;
// keep elementBoundingRect containing rect
elementBoundingRect = rect;
} else if (targetHeight < rect.Height()) {
// Trim the height so that the target rect has the same aspect ratio as
// aMetrics.mVisualViewport, centering it around the user tap point.
float newY = documentRelativePoint.y - (targetHeight * 0.5f);
if ((newY + targetHeight) > rect.YMost()) {
rect.MoveByY(rect.Height() - targetHeight);
} else if (newY > rect.Y()) {
const CSSCoord margin = 15;
rect = AddHMargin(rect, margin, aMetrics.mRootScrollableRect);
if (heightConstrained) {
rect = AddVMargin(rect, margin, aMetrics.mRootScrollableRect);
// If the rect is already taking up most of the visible area and is
// stretching the width of the page, then we want to zoom out instead.
if (RectHasAlmostSameZoomLevel(rect, aMetrics.mVisualViewport)) {
return ZoomTarget{zoomOut, cantZoomOutBehavior, Nothing(),
elementBoundingRect =
AddHMargin(elementBoundingRect, margin, aMetrics.mRootScrollableRect);
// Unlike rect, elementBoundingRect is the full height of the element we are
// zooming to. If we zoom to it without a margin it can look a weird, so give
// it a vertical margin.
elementBoundingRect =
AddVMargin(elementBoundingRect, margin, aMetrics.mRootScrollableRect);
return ZoomTarget{rect, cantZoomOutBehavior, Some(elementBoundingRect),
std::ostream& operator<<(std::ostream& aStream,
const DoubleTapToZoomMetrics& aMetrics) {
aStream << "{ vv=" << aMetrics.mVisualViewport
<< ", rscr=" << aMetrics.mRootScrollableRect
<< ", transform=" << aMetrics.mTransformMatrix << " }";
return aStream;
} // namespace layers
} // namespace mozilla