gecko/layout/base/PositionedEventTargeting.cpp

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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 http://mozilla.org/MPL/2.0/. */
#include "PositionedEventTargeting.h"
#include "mozilla/Preferences.h"
#include "nsGUIEvent.h"
#include "nsLayoutUtils.h"
#include "nsGkAtoms.h"
#include "nsEventListenerManager.h"
#include "nsPrintfCString.h"
#include "mozilla/dom/Element.h"
namespace mozilla {
/*
* The basic goal of FindFrameTargetedByInputEvent() is to find a good
* target element that can respond to mouse events. Both mouse events and touch
* events are targeted at this element. Note that even for touch events, we
* check responsiveness to mouse events. We assume Web authors
* designing for touch events will take their own steps to account for
* inaccurate touch events.
*
* IsElementClickable() encapsulates the heuristic that determines whether an
* element is expected to respond to mouse events. An element is deemed
* "clickable" if it has registered listeners for "click", "mousedown" or
* "mouseup", or is on a whitelist of element tags (<a>, <button>, <input>,
* <select>, <textarea>, <label>), or has role="button", or is a link, or
* is a suitable XUL element.
* Any descendant (in the same document) of a clickable element is also
* deemed clickable since events will propagate to the clickable element from its
* descendant.
*
* If the element directly under the event position is clickable (or
* event radii are disabled), we always use that element. Otherwise we collect
* all frames intersecting a rectangle around the event position (taking CSS
* transforms into account) and choose the best candidate in GetClosest().
* Only IsElementClickable() candidates are considered; if none are found,
* then we revert to targeting the element under the event position.
* We ignore candidates outside the document subtree rooted by the
* document of the element directly under the event position. This ensures that
* event listeners in ancestor documents don't make it completely impossible
* to target a non-clickable element in a child document.
*
* When both a frame and its ancestor are in the candidate list, we ignore
* the ancestor. Otherwise a large ancestor element with a mouse event listener
* and some descendant elements that need to be individually targetable would
* disable intelligent targeting of those descendants within its bounds.
*
* GetClosest() computes the transformed axis-aligned bounds of each
* candidate frame, then computes the Manhattan distance from the event point
* to the bounds rect (which can be zero). The frame with the
* shortest distance is chosen. For visited links we multiply the distance
* by a specified constant weight; this can be used to make visited links
* more or less likely to be targeted than non-visited links.
*/
struct EventRadiusPrefs
{
uint32_t mVisitedWeight; // in percent, i.e. default is 100
uint32_t mSideRadii[4]; // TRBL order, in millimetres
bool mEnabled;
bool mRegistered;
};
static EventRadiusPrefs sMouseEventRadiusPrefs;
static EventRadiusPrefs sTouchEventRadiusPrefs;
static const EventRadiusPrefs*
GetPrefsFor(uint8_t aEventStructType)
{
EventRadiusPrefs* prefs = nullptr;
const char* prefBranch = nullptr;
if (aEventStructType == NS_TOUCH_EVENT) {
prefBranch = "touch";
prefs = &sTouchEventRadiusPrefs;
} else if (aEventStructType == NS_MOUSE_EVENT) {
// Mostly for testing purposes
prefBranch = "mouse";
prefs = &sMouseEventRadiusPrefs;
} else {
return nullptr;
}
if (!prefs->mRegistered) {
prefs->mRegistered = true;
nsPrintfCString enabledPref("ui.%s.radius.enabled", prefBranch);
Preferences::AddBoolVarCache(&prefs->mEnabled, enabledPref.get(), false);
nsPrintfCString visitedWeightPref("ui.%s.radius.visitedWeight", prefBranch);
Preferences::AddUintVarCache(&prefs->mVisitedWeight, visitedWeightPref.get(), 100);
static const char prefNames[4][9] =
{ "topmm", "rightmm", "bottommm", "leftmm" };
for (int32_t i = 0; i < 4; ++i) {
nsPrintfCString radiusPref("ui.%s.radius.%s", prefBranch, prefNames[i]);
Preferences::AddUintVarCache(&prefs->mSideRadii[i], radiusPref.get(), 0);
}
}
return prefs;
}
static bool
HasMouseListener(nsIContent* aContent)
{
nsEventListenerManager* elm = aContent->GetListenerManager(false);
if (!elm) {
return false;
}
return elm->HasListenersFor(nsGkAtoms::onclick) ||
elm->HasListenersFor(nsGkAtoms::onmousedown) ||
elm->HasListenersFor(nsGkAtoms::onmouseup);
}
static bool
IsElementClickable(nsIFrame* aFrame)
{
// Input events propagate up the content tree so we'll follow the content
// ancestors to look for elements accepting the click.
for (nsIContent* content = aFrame->GetContent(); content;
content = content->GetFlattenedTreeParent()) {
if (HasMouseListener(content)) {
return true;
}
if (content->IsHTML()) {
nsIAtom* tag = content->Tag();
if (tag == nsGkAtoms::button ||
tag == nsGkAtoms::input ||
tag == nsGkAtoms::select ||
tag == nsGkAtoms::textarea ||
tag == nsGkAtoms::label) {
return true;
}
} else if (content->IsXUL()) {
nsIAtom* tag = content->Tag();
// See nsCSSFrameConstructor::FindXULTagData. This code is not
// really intended to be used with XUL, though.
if (tag == nsGkAtoms::button ||
tag == nsGkAtoms::checkbox ||
tag == nsGkAtoms::radio ||
tag == nsGkAtoms::autorepeatbutton ||
tag == nsGkAtoms::menu ||
tag == nsGkAtoms::menubutton ||
tag == nsGkAtoms::menuitem ||
tag == nsGkAtoms::menulist ||
tag == nsGkAtoms::scrollbarbutton ||
tag == nsGkAtoms::resizer) {
return true;
}
}
if (content->AttrValueIs(kNameSpaceID_None, nsGkAtoms::role,
nsGkAtoms::button, eIgnoreCase)) {
return true;
}
nsCOMPtr<nsIURI> linkURI;
if (content->IsLink(getter_AddRefs(linkURI))) {
return true;
}
}
return false;
}
static nscoord
AppUnitsFromMM(nsIFrame* aFrame, uint32_t aMM, bool aVertical)
{
nsPresContext* pc = aFrame->PresContext();
nsIPresShell* presShell = pc->PresShell();
float result = float(aMM) *
(pc->DeviceContext()->AppUnitsPerPhysicalInch() / MM_PER_INCH_FLOAT) *
(aVertical ? presShell->GetYResolution() : presShell->GetXResolution());
return NSToCoordRound(result);
}
static nsRect
GetTargetRect(nsIFrame* aRootFrame, const nsPoint& aPointRelativeToRootFrame,
const EventRadiusPrefs* aPrefs)
{
nsMargin m(AppUnitsFromMM(aRootFrame, aPrefs->mSideRadii[3], false),
AppUnitsFromMM(aRootFrame, aPrefs->mSideRadii[0], true),
AppUnitsFromMM(aRootFrame, aPrefs->mSideRadii[1], false),
AppUnitsFromMM(aRootFrame, aPrefs->mSideRadii[2], true));
nsRect r(aPointRelativeToRootFrame, nsSize(0,0));
r.Inflate(m);
return r;
}
static float
ComputeDistanceFromRect(const nsPoint& aPoint, const nsRect& aRect)
{
nscoord dx = NS_MAX(0, NS_MAX(aRect.x - aPoint.x, aPoint.x - aRect.XMost()));
nscoord dy = NS_MAX(0, NS_MAX(aRect.y - aPoint.y, aPoint.y - aRect.YMost()));
return float(NS_hypot(dx, dy));
}
static nsIFrame*
GetClosest(nsIFrame* aRoot, const nsPoint& aPointRelativeToRootFrame,
const EventRadiusPrefs* aPrefs, nsIFrame* aRestrictToDescendants,
nsTArray<nsIFrame*>& aCandidates)
{
nsIFrame* bestTarget = nullptr;
// Lower is better; distance is in appunits
float bestDistance = 1e6f;
for (uint32_t i = 0; i < aCandidates.Length(); ++i) {
nsIFrame* f = aCandidates[i];
if (!IsElementClickable(f)) {
continue;
}
// If our current closest frame is a descendant of 'f', skip 'f' (prefer
// the nested frame).
if (bestTarget && nsLayoutUtils::IsProperAncestorFrameCrossDoc(f, bestTarget, aRoot)) {
continue;
}
if (!nsLayoutUtils::IsAncestorFrameCrossDoc(aRestrictToDescendants, f, aRoot)) {
continue;
}
nsRect borderBox = nsLayoutUtils::TransformFrameRectToAncestor(f,
nsRect(nsPoint(0, 0), f->GetSize()), aRoot);
// distance is in appunits
float distance = ComputeDistanceFromRect(aPointRelativeToRootFrame, borderBox);
nsIContent* content = f->GetContent();
if (content && content->IsElement() &&
content->AsElement()->State().HasState(nsEventStates(NS_EVENT_STATE_VISITED))) {
distance *= aPrefs->mVisitedWeight / 100.0f;
}
if (distance < bestDistance) {
bestDistance = distance;
bestTarget = f;
}
}
return bestTarget;
}
nsIFrame*
FindFrameTargetedByInputEvent(uint8_t aEventStructType,
nsIFrame* aRootFrame,
const nsPoint& aPointRelativeToRootFrame,
uint32_t aFlags)
{
bool ignoreRootScrollFrame = (aFlags & INPUT_IGNORE_ROOT_SCROLL_FRAME) != 0;
nsIFrame* target =
nsLayoutUtils::GetFrameForPoint(aRootFrame, aPointRelativeToRootFrame,
false, ignoreRootScrollFrame);
const EventRadiusPrefs* prefs = GetPrefsFor(aEventStructType);
if (!prefs || !prefs->mEnabled || (target && IsElementClickable(target))) {
return target;
}
nsRect targetRect = GetTargetRect(aRootFrame, aPointRelativeToRootFrame, prefs);
nsAutoTArray<nsIFrame*,8> candidates;
nsresult rv = nsLayoutUtils::GetFramesForArea(aRootFrame, targetRect, candidates,
false, ignoreRootScrollFrame);
if (NS_FAILED(rv)) {
return target;
}
// If the exact target is non-null, only consider candidate targets in the same
// document as the exact target. Otherwise, if an ancestor document has
// a mouse event handler for example, targets that are !IsElementClickable can
// never be targeted --- something nsSubDocumentFrame in an ancestor document
// would be targeted instead.
nsIFrame* restrictToDescendants = target ?
target->PresContext()->PresShell()->GetRootFrame() : aRootFrame;
nsIFrame* closestClickable =
GetClosest(aRootFrame, aPointRelativeToRootFrame, prefs,
restrictToDescendants, candidates);
return closestClickable ? closestClickable : target;
}
}