gecko/gfx/thebes/gfxReusableSurfaceWrapper.h

74 lines
2.2 KiB
C++

/* 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 GFXCOWSURFACEWRAPPER
#define GFXCOWSURFACEWRAPPER
#include "gfxASurface.h"
#include "nsISupportsImpl.h"
#include "nsAutoPtr.h"
#include "mozilla/Atomics.h"
class gfxImageSurface;
/**
* Provides a cross thread wrapper for a gfxImageSurface
* that has copy-on-write schemantics.
*
* Only the owner thread can write to the surface and aquire
* read locks.
*
* OMTC Usage:
* 1) Content creates a writable copy of this surface
* wrapper which be optimized to the same wrapper if there
* are no readers.
* 2) The surface is sent from content to the compositor once
* or potentially many time, each increasing a read lock.
* 3) When the compositor has processed the surface and uploaded
* the content it then releases the read lock.
*/
class gfxReusableSurfaceWrapper {
NS_INLINE_DECL_THREADSAFE_REFCOUNTING(gfxReusableSurfaceWrapper)
public:
/**
* Pass the gfxASurface to the wrapper.
* The wrapper should hold the only strong reference
* to the surface and its memebers.
*/
gfxReusableSurfaceWrapper(gfxImageSurface* aSurface);
~gfxReusableSurfaceWrapper();
const unsigned char* GetReadOnlyData() const {
NS_ABORT_IF_FALSE(mReadCount > 0, "Should have read lock");
return mSurfaceData;
}
const gfxASurface::gfxImageFormat& Format() { return mFormat; }
/**
* Get a writable copy of the image.
* If necessary this will copy the wrapper. If there are no contention
* the same wrapper will be returned.
*/
gfxReusableSurfaceWrapper* GetWritable(gfxImageSurface** aSurface);
/**
* A read only lock count is recorded, any attempts to
* call GetWritable() while this count is positive will
* create a new surface/wrapper pair.
*/
void ReadLock();
void ReadUnlock();
private:
NS_DECL_OWNINGTHREAD
nsRefPtr<gfxImageSurface> mSurface;
const gfxASurface::gfxImageFormat mFormat;
const unsigned char* mSurfaceData;
mozilla::Atomic<int32_t> mReadCount;
};
#endif // GFXCOWSURFACEWRAPPER