1 files changed, 468 insertions, 0 deletions
diff --git a/layout/base/DisplayListClipState.h b/layout/base/DisplayListClipState.h
new file mode 100644
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+++ b/layout/base/DisplayListClipState.h
@@ -0,0 +1,468 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * 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/. */
+
+#ifndef DISPLAYLISTCLIPSTATE_H_
+#define DISPLAYLISTCLIPSTATE_H_
+
+#include "DisplayItemClip.h"
+#include "DisplayItemScrollClip.h"
+
+#include "mozilla/DebugOnly.h"
+
+class nsIFrame;
+class nsIScrollableFrame;
+class nsDisplayListBuilder;
+
+namespace mozilla {
+
+/**
+ * All clip coordinates are in appunits relative to the reference frame
+ * for the display item we're building.
+ */
+class DisplayListClipState {
+public:
+  DisplayListClipState()
+    : mClipContentDescendants(nullptr)
+    , mClipContainingBlockDescendants(nullptr)
+    , mCurrentCombinedClip(nullptr)
+    , mScrollClipContentDescendants(nullptr)
+    , mScrollClipContainingBlockDescendants(nullptr)
+    , mClipContentDescendantsScrollClip(nullptr)
+    , mStackingContextAncestorSC(nullptr)
+  {}
+
+  /**
+   * Returns intersection of mClipContainingBlockDescendants and
+   * mClipContentDescendants, allocated on aBuilder's arena.
+   */
+  const DisplayItemClip* GetCurrentCombinedClip(nsDisplayListBuilder* aBuilder);
+
+  const DisplayItemClip* GetClipForContainingBlockDescendants() const
+  {
+    return mClipContainingBlockDescendants;
+  }
+  const DisplayItemClip* GetClipForContentDescendants() const
+  {
+    return mClipContentDescendants;
+  }
+
+  const DisplayItemScrollClip* GetCurrentInnermostScrollClip();
+
+  const DisplayItemScrollClip* CurrentAncestorScrollClipForStackingContextContents()
+  {
+    return mStackingContextAncestorSC;
+  }
+
+  class AutoSaveRestore;
+  friend class AutoSaveRestore;
+
+  class AutoClipContainingBlockDescendantsToContentBox;
+  friend class AutoClipContainingBlockDescendantsToContentBox;
+
+  class AutoClipMultiple;
+  friend class AutoClipMultiple;
+
+  enum {
+    ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT = 0x01
+  };
+
+private:
+  void SetClipForContainingBlockDescendants(const DisplayItemClip* aClip)
+  {
+    mClipContainingBlockDescendants = aClip;
+    mCurrentCombinedClip = nullptr;
+  }
+
+  void SetScrollClipForContainingBlockDescendants(nsDisplayListBuilder* aBuilder,
+                                                  const DisplayItemScrollClip* aScrollClip);
+
+  void Clear()
+  {
+    mClipContentDescendants = nullptr;
+    mClipContainingBlockDescendants = nullptr;
+    mCurrentCombinedClip = nullptr;
+    // We do not clear scroll clips.
+  }
+
+  void EnterStackingContextContents(bool aClear)
+  {
+    if (aClear) {
+      mClipContentDescendants = nullptr;
+      mClipContainingBlockDescendants = nullptr;
+      mCurrentCombinedClip = nullptr;
+      mScrollClipContentDescendants = nullptr;
+      mScrollClipContainingBlockDescendants = nullptr;
+      mStackingContextAncestorSC = nullptr;
+    } else {
+      mStackingContextAncestorSC = GetCurrentInnermostScrollClip();
+    }
+  }
+
+  /**
+   * Clear the current clip, and instead add it as a scroll clip to the current
+   * scroll clip chain.
+   */
+  void TurnClipIntoScrollClipForContentDescendants(nsDisplayListBuilder* aBuilder,
+                                                   nsIScrollableFrame* aScrollableFrame);
+  void TurnClipIntoScrollClipForContainingBlockDescendants(nsDisplayListBuilder* aBuilder,
+                                                           nsIScrollableFrame* aScrollableFrame);
+
+  /**
+   * Insert a scroll clip without clearing the current clip.
+   * The returned DisplayItemScrollClip will have mIsAsyncScrollable == false,
+   * and it can be activated once the scroll frame knows that it needs to be
+   * async scrollable.
+   */
+  DisplayItemScrollClip* InsertInactiveScrollClipForContentDescendants(nsDisplayListBuilder* aBuilder,
+                                                                       nsIScrollableFrame* aScrollableFrame);
+  DisplayItemScrollClip* InsertInactiveScrollClipForContainingBlockDescendants(nsDisplayListBuilder* aBuilder,
+                                                                               nsIScrollableFrame* aScrollableFrame);
+
+  DisplayItemScrollClip* CreateInactiveScrollClip(nsDisplayListBuilder* aBuilder,
+                                                  nsIScrollableFrame* aScrollableFrame);
+
+  /**
+   * Intersects the given clip rect (with optional aRadii) with the current
+   * mClipContainingBlockDescendants and sets mClipContainingBlockDescendants to
+   * the result, stored in aClipOnStack.
+   */
+  void ClipContainingBlockDescendants(const nsRect& aRect,
+                                      const nscoord* aRadii,
+                                      DisplayItemClip& aClipOnStack);
+
+  void ClipContentDescendants(const nsRect& aRect,
+                              const nscoord* aRadii,
+                              DisplayItemClip& aClipOnStack);
+  void ClipContentDescendants(const nsRect& aRect,
+                              const nsRect& aRoundedRect,
+                              const nscoord* aRadii,
+                              DisplayItemClip& aClipOnStack);
+
+  /**
+   * Clips containing-block descendants to the frame's content-box,
+   * taking border-radius into account.
+   * If aFlags contains ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT then
+   * we assume display items will not draw outside the content rect, so
+   * clipping is only required if there is a border-radius. This is an
+   * optimization to reduce the amount of clipping required.
+   */
+  void ClipContainingBlockDescendantsToContentBox(nsDisplayListBuilder* aBuilder,
+                                                  nsIFrame* aFrame,
+                                                  DisplayItemClip& aClipOnStack,
+                                                  uint32_t aFlags);
+
+  /**
+   * All content descendants (i.e. following placeholder frames to their
+   * out-of-flows if necessary) should be clipped by mClipContentDescendants.
+   * Null if no clipping applies.
+   */
+  const DisplayItemClip* mClipContentDescendants;
+  /**
+   * All containing-block descendants (i.e. frame descendants), including
+   * display items for the current frame, should be clipped by
+   * mClipContainingBlockDescendants.
+   * Null if no clipping applies.
+   */
+  const DisplayItemClip* mClipContainingBlockDescendants;
+  /**
+   * The intersection of mClipContentDescendants and
+   * mClipContainingBlockDescendants.
+   * Allocated in the nsDisplayListBuilder arena. Null if none has been
+   * allocated or both mClipContentDescendants and mClipContainingBlockDescendants
+   * are null.
+   */
+  const DisplayItemClip* mCurrentCombinedClip;
+
+  /**
+   * The same for scroll clips.
+   */
+  const DisplayItemScrollClip* mScrollClipContentDescendants;
+  const DisplayItemScrollClip* mScrollClipContainingBlockDescendants;
+
+  /**
+   * The scroll clip that was in effect when mClipContentDescendants was set.
+   */
+  const DisplayItemScrollClip* mClipContentDescendantsScrollClip;
+
+  /**
+   * A scroll clip that is an ancestor of all the scroll clips that were
+   * "current" on this clip state since EnterStackingContextContents was
+   * called.
+   */
+  const DisplayItemScrollClip* mStackingContextAncestorSC;
+};
+
+/**
+ * A class to automatically save and restore the current clip state. Also
+ * offers methods for modifying the clip state. Only one modification is allowed
+ * to be in scope at a time using one of these objects; multiple modifications
+ * require nested objects. The interface is written this way to prevent
+ * dangling pointers to DisplayItemClips.
+ */
+class DisplayListClipState::AutoSaveRestore {
+public:
+  explicit AutoSaveRestore(nsDisplayListBuilder* aBuilder);
+  void Restore()
+  {
+    if (!mClearedForStackingContextContents) {
+      // Forward along the ancestor scroll clip to the original clip state.
+      mSavedState.mStackingContextAncestorSC =
+        DisplayItemScrollClip::PickAncestor(mSavedState.mStackingContextAncestorSC,
+                                            mState.mStackingContextAncestorSC);
+    }
+    mState = mSavedState;
+#ifdef DEBUG
+    mRestored = true;
+#endif
+  }
+  ~AutoSaveRestore()
+  {
+    Restore();
+  }
+
+  void Clear()
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    mState.Clear();
+#ifdef DEBUG
+    mClipUsed = false;
+#endif
+  }
+
+  void EnterStackingContextContents(bool aClear)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    mState.EnterStackingContextContents(aClear);
+    mClearedForStackingContextContents = aClear;
+  }
+
+  void ExitStackingContextContents(const DisplayItemScrollClip** aOutContainerSC)
+  {
+    if (mClearedForStackingContextContents) {
+      // If we cleared the scroll clip, then the scroll clip that was current
+      // just before we cleared it is the one that needs to be set on the
+      // container item.
+      *aOutContainerSC = mSavedState.GetCurrentInnermostScrollClip();
+    } else {
+      // If we didn't clear the scroll clip, then the container item needs to
+      // get a scroll clip that's an ancestor of all its direct child items'
+      // scroll clips.
+      // The simplest way to satisfy this requirement would be to just take the
+      // root scroll clip (i.e. nullptr). However, this can cause the bounds of
+      // the container items to be enlarged unnecessarily, so instead we try to
+      // take the "deepest" scroll clip that satisfies the requirement.
+      // Usually this is the scroll clip that was current before we entered
+      // the stacking context contents (call that the "initial scroll clip").
+      // There are two cases in which the container scroll clip *won't* be the
+      // initial scroll clip (instead the container scroll clip will be a
+      // proper ancestor of the initial scroll clip):
+      //  (1) If SetScrollClipForContainingBlockDescendants was called with an
+      //      ancestor scroll clip of the initial scroll clip while we were
+      //      building our direct child items. This happens if we entered a
+      //      position:absolute or position:fixed element whose containing
+      //      block is an ancestor of the frame that generated the initial
+      //      scroll clip. Then the "ancestor scroll clip for stacking context
+      //      contents" will be set to that scroll clip.
+      //  (2) If one of our direct child items is a container item for which
+      //      (1) or (2) happened.
+      *aOutContainerSC = mState.CurrentAncestorScrollClipForStackingContextContents();
+    }
+    Restore();
+  }
+
+  bool SavedStateHasRoundedCorners()
+  {
+    const DisplayItemScrollClip* scrollClip = mSavedState.GetCurrentInnermostScrollClip();
+    if (scrollClip && scrollClip->HasRoundedCorners()) {
+      return true;
+    }
+    const DisplayItemClip* clip = mSavedState.GetClipForContainingBlockDescendants();
+    if (clip && clip->GetRoundedRectCount() > 0) {
+      return true;
+    }
+
+    clip = mSavedState.GetClipForContentDescendants();
+    if (clip && clip->GetRoundedRectCount() > 0) {
+      return true;
+    }
+    return false;
+  }
+
+  void TurnClipIntoScrollClipForContentDescendants(nsDisplayListBuilder* aBuilder, nsIScrollableFrame* aScrollableFrame)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    mState.TurnClipIntoScrollClipForContentDescendants(aBuilder, aScrollableFrame);
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+  }
+
+  void TurnClipIntoScrollClipForContainingBlockDescendants(nsDisplayListBuilder* aBuilder, nsIScrollableFrame* aScrollableFrame)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    mState.TurnClipIntoScrollClipForContainingBlockDescendants(aBuilder, aScrollableFrame);
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+  }
+
+  DisplayItemScrollClip* InsertInactiveScrollClipForContentDescendants(nsDisplayListBuilder* aBuilder, nsIScrollableFrame* aScrollableFrame)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    DisplayItemScrollClip* scrollClip = mState.InsertInactiveScrollClipForContentDescendants(aBuilder, aScrollableFrame);
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    return scrollClip;
+  }
+
+  DisplayItemScrollClip* InsertInactiveScrollClipForContainingBlockDescendants(nsDisplayListBuilder* aBuilder, nsIScrollableFrame* aScrollableFrame)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    DisplayItemScrollClip* scrollClip = mState.InsertInactiveScrollClipForContainingBlockDescendants(aBuilder, aScrollableFrame);
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    return scrollClip;
+  }
+
+  /**
+   * Intersects the given clip rect (with optional aRadii) with the current
+   * mClipContainingBlockDescendants and sets mClipContainingBlockDescendants to
+   * the result, stored in aClipOnStack.
+   */
+  void ClipContainingBlockDescendants(const nsRect& aRect,
+                                      const nscoord* aRadii = nullptr)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendants(aRect, aRadii, mClip);
+  }
+
+  void ClipContentDescendants(const nsRect& aRect,
+                              const nscoord* aRadii = nullptr)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContentDescendants(aRect, aRadii, mClip);
+  }
+
+  void ClipContentDescendants(const nsRect& aRect,
+                              const nsRect& aRoundedRect,
+                              const nscoord* aRadii = nullptr)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContentDescendants(aRect, aRoundedRect, aRadii, mClip);
+  }
+
+  /**
+   * Clips containing-block descendants to the frame's content-box,
+   * taking border-radius into account.
+   * If aFlags contains ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT then
+   * we assume display items will not draw outside the content rect, so
+   * clipping is only required if there is a border-radius. This is an
+   * optimization to reduce the amount of clipping required.
+   */
+  void ClipContainingBlockDescendantsToContentBox(nsDisplayListBuilder* aBuilder,
+                                                  nsIFrame* aFrame,
+                                                  uint32_t aFlags = 0)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendantsToContentBox(aBuilder, aFrame, mClip, aFlags);
+  }
+
+protected:
+  DisplayListClipState& mState;
+  DisplayListClipState mSavedState;
+  DisplayItemClip mClip;
+#ifdef DEBUG
+  bool mClipUsed;
+  bool mRestored;
+#endif
+  bool mClearedForStackingContextContents;
+};
+
+class DisplayListClipState::AutoClipContainingBlockDescendantsToContentBox : public AutoSaveRestore {
+public:
+  AutoClipContainingBlockDescendantsToContentBox(nsDisplayListBuilder* aBuilder,
+                                                 nsIFrame* aFrame,
+                                                 uint32_t aFlags = 0)
+    : AutoSaveRestore(aBuilder)
+  {
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendantsToContentBox(aBuilder, aFrame, mClip, aFlags);
+  }
+};
+
+/**
+ * Do not use this outside of nsFrame::BuildDisplayListForChild, use
+ * multiple AutoSaveRestores instead. We provide this class just to ensure
+ * BuildDisplayListForChild is as efficient as possible.
+ */
+class DisplayListClipState::AutoClipMultiple : public AutoSaveRestore {
+public:
+  explicit AutoClipMultiple(nsDisplayListBuilder* aBuilder)
+    : AutoSaveRestore(aBuilder)
+#ifdef DEBUG
+    , mExtraClipUsed(false)
+#endif
+  {}
+
+  /**
+   * *aClip must survive longer than this object. Be careful!!!
+   */
+  void SetClipForContainingBlockDescendants(const DisplayItemClip* aClip)
+  {
+    mState.SetClipForContainingBlockDescendants(aClip);
+  }
+
+  void SetScrollClipForContainingBlockDescendants(nsDisplayListBuilder* aBuilder,
+                                                  const DisplayItemScrollClip* aScrollClip)
+  {
+    mState.SetScrollClipForContainingBlockDescendants(aBuilder, aScrollClip);
+  }
+
+  /**
+   * Intersects the given clip rect (with optional aRadii) with the current
+   * mClipContainingBlockDescendants and sets mClipContainingBlockDescendants to
+   * the result, stored in aClipOnStack.
+   */
+  void ClipContainingBlockDescendantsExtra(const nsRect& aRect,
+                                           const nscoord* aRadii)
+  {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mExtraClipUsed, "mExtraClip already used");
+#ifdef DEBUG
+    mExtraClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendants(aRect, aRadii, mExtraClip);
+  }
+
+protected:
+  DisplayItemClip mExtraClip;
+#ifdef DEBUG
+  bool mExtraClipUsed;
+#endif
+};
+
+} // namespace mozilla
+
+#endif /* DISPLAYLISTCLIPSTATE_H_ */