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