diff -r 000000000000 -r 6474c204b198 layout/base/PositionedEventTargeting.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/base/PositionedEventTargeting.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,402 @@
+/* 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/EventListenerManager.h"
+#include "mozilla/EventStates.h"
+#include "mozilla/MouseEvents.h"
+#include "mozilla/Preferences.h"
+#include "nsLayoutUtils.h"
+#include "nsGkAtoms.h"
+#include "nsPrintfCString.h"
+#include "mozilla/dom/Element.h"
+#include "nsRegion.h"
+#include "nsDeviceContext.h"
+#include "nsIFrame.h"
+#include <algorithm>
+
+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;
+  bool mTouchOnly;
+};
+
+static EventRadiusPrefs sMouseEventRadiusPrefs;
+static EventRadiusPrefs sTouchEventRadiusPrefs;
+
+static const EventRadiusPrefs*
+GetPrefsFor(nsEventStructType 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);
+    }
+
+    if (aEventStructType == NS_MOUSE_EVENT) {
+      Preferences::AddBoolVarCache(&prefs->mTouchOnly,
+          "ui.mouse.radius.inputSource.touchOnly", true);
+    } else {
+      prefs->mTouchOnly = false;
+    }
+  }
+
+  return prefs;
+}
+
+static bool
+HasMouseListener(nsIContent* aContent)
+{
+  if (EventListenerManager* elm = aContent->GetExistingListenerManager()) {
+    return elm->HasListenersFor(nsGkAtoms::onclick) ||
+           elm->HasListenersFor(nsGkAtoms::onmousedown) ||
+           elm->HasListenersFor(nsGkAtoms::onmouseup);
+  }
+
+  return false;
+}
+
+static bool gTouchEventsRegistered = false;
+static int32_t gTouchEventsEnabled = 0;
+
+static bool
+HasTouchListener(nsIContent* aContent)
+{
+  EventListenerManager* elm = aContent->GetExistingListenerManager();
+  if (!elm) {
+    return false;
+  }
+
+  if (!gTouchEventsRegistered) {
+    Preferences::AddIntVarCache(&gTouchEventsEnabled,
+      "dom.w3c_touch_events.enabled", gTouchEventsEnabled);
+    gTouchEventsRegistered = true;
+  }
+
+  if (!gTouchEventsEnabled) {
+    return false;
+  }
+
+  return elm->HasListenersFor(nsGkAtoms::ontouchstart) ||
+         elm->HasListenersFor(nsGkAtoms::ontouchend);
+}
+
+static bool
+IsElementClickable(nsIFrame* aFrame, nsIAtom* stopAt = nullptr)
+{
+  // 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()) {
+    nsIAtom* tag = content->Tag();
+    if (content->IsHTML() && stopAt && tag == stopAt) {
+      break;
+    }
+    if (HasTouchListener(content) || HasMouseListener(content)) {
+      return true;
+    }
+    if (content->IsHTML()) {
+      if (tag == nsGkAtoms::button ||
+          tag == nsGkAtoms::input ||
+          tag == nsGkAtoms::select ||
+          tag == nsGkAtoms::textarea ||
+          tag == nsGkAtoms::label) {
+        return true;
+      }
+      // Bug 921928: we don't have access to the content of remote iframe.
+      // So fluffing won't go there. We do an optimistic assumption here:
+      // that the content of the remote iframe needs to be a target.
+      if (tag == nsGkAtoms::iframe &&
+          content->AttrValueIs(kNameSpaceID_None, nsGkAtoms::mozbrowser,
+                               nsGkAtoms::_true, eIgnoreCase) &&
+          content->AttrValueIs(kNameSpaceID_None, nsGkAtoms::Remote,
+                               nsGkAtoms::_true, eIgnoreCase)) {
+        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;
+      }
+    }
+    static nsIContent::AttrValuesArray clickableRoles[] =
+      { &nsGkAtoms::button, &nsGkAtoms::key, nullptr };
+    if (content->FindAttrValueIn(kNameSpaceID_None, nsGkAtoms::role,
+                                 clickableRoles, eIgnoreCase) >= 0) {
+      return true;
+    }
+    if (content->IsEditable()) {
+      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();
+  float result = float(aMM) *
+    (pc->DeviceContext()->AppUnitsPerPhysicalInch() / MM_PER_INCH_FLOAT);
+  return NSToCoordRound(result);
+}
+
+/**
+ * Clip aRect with the bounds of aFrame in the coordinate system of
+ * aRootFrame. aRootFrame is an ancestor of aFrame.
+ */
+static nsRect
+ClipToFrame(nsIFrame* aRootFrame, nsIFrame* aFrame, nsRect& aRect)
+{
+  nsRect bound = nsLayoutUtils::TransformFrameRectToAncestor(
+    aFrame, nsRect(nsPoint(0, 0), aFrame->GetSize()), aRootFrame);
+  nsRect result = bound.Intersect(aRect);
+  return result;
+}
+
+static nsRect
+GetTargetRect(nsIFrame* aRootFrame, const nsPoint& aPointRelativeToRootFrame,
+              nsIFrame* aRestrictToDescendants, const EventRadiusPrefs* aPrefs)
+{
+  nsMargin m(AppUnitsFromMM(aRootFrame, aPrefs->mSideRadii[0], true),
+             AppUnitsFromMM(aRootFrame, aPrefs->mSideRadii[1], false),
+             AppUnitsFromMM(aRootFrame, aPrefs->mSideRadii[2], true),
+             AppUnitsFromMM(aRootFrame, aPrefs->mSideRadii[3], false));
+  nsRect r(aPointRelativeToRootFrame, nsSize(0,0));
+  r.Inflate(m);
+  return ClipToFrame(aRootFrame, aRestrictToDescendants, r);
+}
+
+static float
+ComputeDistanceFromRect(const nsPoint& aPoint, const nsRect& aRect)
+{
+  nscoord dx = std::max(0, std::max(aRect.x - aPoint.x, aPoint.x - aRect.XMost()));
+  nscoord dy = std::max(0, std::max(aRect.y - aPoint.y, aPoint.y - aRect.YMost()));
+  return float(NS_hypot(dx, dy));
+}
+
+static float
+ComputeDistanceFromRegion(const nsPoint& aPoint, const nsRegion& aRegion)
+{
+  MOZ_ASSERT(!aRegion.IsEmpty(), "can't compute distance between point and empty region");
+  nsRegionRectIterator iter(aRegion);
+  const nsRect* r;
+  float minDist = -1;
+  while ((r = iter.Next()) != nullptr) {
+    float dist = ComputeDistanceFromRect(aPoint, *r);
+    if (dist < minDist || minDist < 0) {
+      minDist = dist;
+    }
+  }
+  return minDist;
+}
+
+// Subtract aRegion from aExposedRegion as long as that doesn't make the
+// exposed region get too complex or removes a big chunk of the exposed region.
+static void
+SubtractFromExposedRegion(nsRegion* aExposedRegion, const nsRegion& aRegion)
+{
+  if (aRegion.IsEmpty())
+    return;
+
+  nsRegion tmp;
+  tmp.Sub(*aExposedRegion, aRegion);
+  // Don't let *aExposedRegion get too complex, but don't let it fluff out to
+  // its bounds either. Do let aExposedRegion get more complex if by doing so
+  // we reduce its area by at least half.
+  if (tmp.GetNumRects() <= 15 || tmp.Area() <= aExposedRegion->Area()/2) {
+    *aExposedRegion = tmp;
+  }
+}
+
+static nsIFrame*
+GetClosest(nsIFrame* aRoot, const nsPoint& aPointRelativeToRootFrame,
+           const nsRect& aTargetRect, const EventRadiusPrefs* aPrefs,
+           nsIFrame* aRestrictToDescendants, nsTArray<nsIFrame*>& aCandidates)
+{
+  nsIFrame* bestTarget = nullptr;
+  // Lower is better; distance is in appunits
+  float bestDistance = 1e6f;
+  nsRegion exposedRegion(aTargetRect);
+  for (uint32_t i = 0; i < aCandidates.Length(); ++i) {
+    nsIFrame* f = aCandidates[i];
+
+    bool preservesAxisAlignedRectangles = false;
+    nsRect borderBox = nsLayoutUtils::TransformFrameRectToAncestor(f,
+        nsRect(nsPoint(0, 0), f->GetSize()), aRoot, &preservesAxisAlignedRectangles);
+    nsRegion region;
+    region.And(exposedRegion, borderBox);
+
+    if (region.IsEmpty()) {
+      continue;
+    }
+
+    if (preservesAxisAlignedRectangles) {
+      // Subtract from the exposed region if we have a transform that won't make
+      // the bounds include a bunch of area that we don't actually cover.
+      SubtractFromExposedRegion(&exposedRegion, region);
+    }
+
+    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;
+    }
+
+    // distance is in appunits
+    float distance = ComputeDistanceFromRegion(aPointRelativeToRootFrame, region);
+    nsIContent* content = f->GetContent();
+    if (content && content->IsElement() &&
+        content->AsElement()->State().HasState(
+                                        EventStates(NS_EVENT_STATE_VISITED))) {
+      distance *= aPrefs->mVisitedWeight / 100.0f;
+    }
+    if (distance < bestDistance) {
+      bestDistance = distance;
+      bestTarget = f;
+    }
+  }
+  return bestTarget;
+}
+
+nsIFrame*
+FindFrameTargetedByInputEvent(const WidgetGUIEvent* aEvent,
+                              nsIFrame* aRootFrame,
+                              const nsPoint& aPointRelativeToRootFrame,
+                              uint32_t aFlags)
+{
+  uint32_t flags = (aFlags & INPUT_IGNORE_ROOT_SCROLL_FRAME) ?
+     nsLayoutUtils::IGNORE_ROOT_SCROLL_FRAME : 0;
+  nsIFrame* target =
+    nsLayoutUtils::GetFrameForPoint(aRootFrame, aPointRelativeToRootFrame, flags);
+
+  const EventRadiusPrefs* prefs = GetPrefsFor(aEvent->eventStructType);
+  if (!prefs || !prefs->mEnabled || (target && IsElementClickable(target, nsGkAtoms::body))) {
+    return target;
+  }
+
+  // Do not modify targeting for actual mouse hardware; only for mouse
+  // events generated by touch-screen hardware.
+  if (aEvent->eventStructType == NS_MOUSE_EVENT &&
+      prefs->mTouchOnly &&
+      aEvent->AsMouseEvent()->inputSource !=
+        nsIDOMMouseEvent::MOZ_SOURCE_TOUCH) {
+    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;
+
+  nsRect targetRect = GetTargetRect(aRootFrame, aPointRelativeToRootFrame,
+                                    restrictToDescendants, prefs);
+  nsAutoTArray<nsIFrame*,8> candidates;
+  nsresult rv = nsLayoutUtils::GetFramesForArea(aRootFrame, targetRect, candidates, flags);
+  if (NS_FAILED(rv)) {
+    return target;
+  }
+
+  nsIFrame* closestClickable =
+    GetClosest(aRootFrame, aPointRelativeToRootFrame, targetRect, prefs,
+               restrictToDescendants, candidates);
+  return closestClickable ? closestClickable : target;
+}
+
+}