The Tor Browser: gfx/thebes/gfxReusableSurfaceWrapper.h@b8a032363ba2

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

     1 /* This Source Code Form is subject to the terms of the Mozilla Public

     2  * License, v. 2.0. If a copy of the MPL was not distributed with this file,

     3  * You can obtain one at http://mozilla.org/MPL/2.0/. */

     5 #ifndef GFXCOWSURFACEWRAPPER

     6 #define GFXCOWSURFACEWRAPPER

     8 #include "gfxImageSurface.h"

     9 #include "nsISupportsImpl.h"

    10 #include "nsAutoPtr.h"

    13 /**

    14  * Provides an interface to implement a cross thread/process wrapper for a

    15  * gfxImageSurface that has copy-on-write semantics.

    16  *

    17  * Only the owner thread can write to the surface and acquire

    18  * read locks. Destroying a gfxReusableSurfaceWrapper releases

    19  * a read lock.

    20  *

    21  * OMTC Usage:

    22  * 1) Content creates a writable copy of this surface

    23  *    wrapper which will be optimized to the same wrapper if there

    24  *    are no readers.

    25  * 2) The surface is sent from content to the compositor once

    26  *    or potentially many times, each increasing a read lock.

    27  * 3) When the compositor receives the surface, it adopts the

    28  *    read lock.

    29  * 4) Once the compositor has processed the surface and uploaded

    30  *    the content, it then releases the read lock by dereferencing

    31  *    its wrapper.

    32  */

    33 class gfxReusableSurfaceWrapper {

    34   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(gfxReusableSurfaceWrapper)

    35 public:

    37   /**

    38    * Returns a read-only pointer to the image data.

    39    */

    40   virtual const unsigned char* GetReadOnlyData() const = 0;

    42   /**

    43    * Returns the image surface format.

    44    */

    45   virtual gfxImageFormat Format() = 0;

    47   /**

    48    * Returns a writable copy of the image.

    49    * If necessary this will copy the wrapper. If there are no contention

    50    * the same wrapper will be returned. A ReadLock must be held when

    51    * calling this function, and calling it will give up this lock.

    52    */

    53   virtual gfxReusableSurfaceWrapper* GetWritable(gfxImageSurface** aSurface) = 0;

    55   /**

    56    * A read only lock count is recorded, any attempts to

    57    * call GetWritable() while this count is greater than one will

    58    * create a new surface/wrapper pair.

    59    *

    60    * When a surface's read count falls to zero, its memory will be

    61    * deallocated. It is the responsibility of the user to make sure

    62    * that all locks are matched with an equal number of unlocks.

    63    */

    64   virtual void ReadLock() = 0;

    65   virtual void ReadUnlock() = 0;

    67   /**

    68    * Types for each implementation of gfxReusableSurfaceWrapper.

    69    */

    70   enum Type {

    71     TYPE_SHARED_IMAGE,

    72     TYPE_IMAGE,

    74     TYPE_MAX

    75   };

    77   /**

    78    * Returns a unique ID for each implementation of gfxReusableSurfaceWrapper.

    79    */

    80   virtual Type GetType() = 0;

    82 protected:

    83   // Protected destructor, to discourage deletion outside of Release():

    84   virtual ~gfxReusableSurfaceWrapper() {}

    86   NS_DECL_OWNINGTHREAD

    87 };

    89 #endif // GFXCOWSURFACEWRAPPER

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