127 lines
4.5 KiB
C++
127 lines
4.5 KiB
C++
/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef DISPLAYITEMSCROLLCLIP_H_
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#define DISPLAYITEMSCROLLCLIP_H_
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#include "mozilla/Assertions.h"
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#include "nsString.h"
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class nsIScrollableFrame;
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namespace mozilla {
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class DisplayItemClip;
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/**
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* A DisplayItemScrollClip represents a DisplayItemClip from a scrollable
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* frame. This clip is stored on a display item separately from the item's
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* regular DisplayItemClip for async scrolling purposes: The item's regular
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* clip can be fused to the item's contents when drawing layer contents, but
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* scroll clips need to be kept separate so that they can be applied at
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* composition time, after any async scroll offsets have been applied.
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* Scroll clips are created during display list construction when
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* async-scrollable scroll frames are entered. At that point, the current
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* regular clip is cleared on the display list clip state. They are also
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* created for scroll frames that are inactivate and not async scrollable;
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* in that case, mIsAsyncScrollable on the scroll clip will be false.
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* When async-scrollable scroll frames are nested, the inner display items
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* can walk the whole chain of scroll clips via the DisplayItemScrollClip's
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* mParent pointer.
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* Storing scroll clips on display items allows easy access of all scroll
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* frames that affect a certain display item, and it allows some display list
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* operations to compute more accurate clips, for example when computing the
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* bounds of a container item for a frame that contains an async-scrollable
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* scroll frame.
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*/
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class DisplayItemScrollClip {
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public:
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DisplayItemScrollClip(const DisplayItemScrollClip* aParent,
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nsIScrollableFrame* aScrollableFrame,
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const DisplayItemClip* aClip,
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bool aIsAsyncScrollable)
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: mParent(aParent)
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, mScrollableFrame(aScrollableFrame)
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, mClip(aClip)
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, mIsAsyncScrollable(aIsAsyncScrollable)
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, mDepth(aParent ? aParent->mDepth + 1 : 1)
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{
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MOZ_ASSERT(mScrollableFrame);
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}
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/**
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* "Pick descendant" is analogous to the intersection operation on regular
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* clips: In some cases, there are multiple candidate clips that can apply to
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* an item, one of them being the ancestor of the other. This method picks
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* the descendant.
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* Both aClip1 and aClip2 are allowed to be null.
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*/
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static const DisplayItemScrollClip*
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PickDescendant(const DisplayItemScrollClip* aClip1,
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const DisplayItemScrollClip* aClip2)
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{
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MOZ_ASSERT(IsAncestor(aClip1, aClip2) || IsAncestor(aClip2, aClip1),
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"one of the scroll clips must be an ancestor of the other");
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return Depth(aClip1) > Depth(aClip2) ? aClip1 : aClip2;
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}
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static const DisplayItemScrollClip*
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PickAncestor(const DisplayItemScrollClip* aClip1,
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const DisplayItemScrollClip* aClip2)
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{
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MOZ_ASSERT(IsAncestor(aClip1, aClip2) || IsAncestor(aClip2, aClip1),
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"one of the scroll clips must be an ancestor of the other");
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return Depth(aClip1) < Depth(aClip2) ? aClip1 : aClip2;
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}
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/**
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* Returns whether aAncestor is an ancestor scroll clip of aDescendant.
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* A scroll clip that's null is considered the root scroll clip.
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*/
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static bool IsAncestor(const DisplayItemScrollClip* aAncestor,
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const DisplayItemScrollClip* aDescendant);
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/**
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* Return a string which contains the list of stringified clips for this
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* scroll clip and its ancestors. aScrollClip can be null.
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*/
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static nsCString ToString(const DisplayItemScrollClip* aScrollClip);
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bool HasRoundedCorners() const;
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/**
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* The previous (outer) scroll clip, or null.
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*/
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const DisplayItemScrollClip* mParent;
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/**
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* The scrollable frame that this scroll clip is for. Always non-null.
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*/
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nsIScrollableFrame* mScrollableFrame;
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/**
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* The clip represented by this scroll clip, relative to mScrollableFrame's
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* reference frame. Can be null.
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*/
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const DisplayItemClip* mClip;
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/**
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* Whether this scroll clip is for an async-scrollable scroll frame.
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* Can change during display list construction.
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*/
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bool mIsAsyncScrollable;
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private:
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static uint32_t Depth(const DisplayItemScrollClip* aSC)
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{ return aSC ? aSC->mDepth : 0; }
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const uint32_t mDepth;
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};
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} // namespace mozilla
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#endif /* DISPLAYITEMSCROLLCLIP_H_ */
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