gfx/thebes/gfxCachedTempSurface.h

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  21  * Contributor(s):
  22  *   Karl Tomlinson <karlt+@karlt.net>
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  37
  38 #ifndef GFX_CACHED_TEMP_SURFACE_H
  39 #define GFX_CACHED_TEMP_SURFACE_H
  40
  41 #include "gfxASurface.h"
  42 #include "nsExpirationTracker.h"
  43
  44 class gfxContext;
  45
  46 /**
  47  * This class can be used to cache double-buffering back surfaces.
  48  *
  49  * Large resource allocations may have an overhead that can be avoided by
  50  * caching.  Caching also alows the system to use history in deciding whether
  51  * to manage the surfaces in video or system memory.
  52  *
  53  * However, because we don't want to set aside megabytes of unused resources
  54  * unncessarily, these surfaces are released on a timer.
  55  */
  56
  57 class THEBES_API gfxCachedTempSurface {
  58 public:
  59   /**
  60    * Returns a context for a surface that can be efficiently copied to
  61    * |aSimilarTo|.
  62    *
  63    * When |aContentType| has an alpha component, the surface will be cleared.
  64    * For opaque surfaces, the initial surface contents are undefined.
  65    * When |aContentType| differs in different invocations this is handled
  66    * appropriately, creating a new surface if necessary.
  67    *
  68    * |aSimilarTo| should be of the same gfxSurfaceType in each invocation.
  69    * Because the cached surface may have been created during a previous
  70    * invocation, this will not be efficient if the new |aSimilarTo| has a
  71    * different format.
  72    */
  73   already_AddRefed<gfxContext> Get(gfxASurface::gfxContentType aContentType,
  74                                    const gfxIntSize& aSize,
  75                                    gfxASurface* aSimilarTo);
  76
  77   void Expire() { mSurface = nsnull; }
  78   nsExpirationState* GetExpirationState() { return &mExpirationState; }
  79   ~gfxCachedTempSurface();
  80
  81 private:
  82   nsRefPtr<gfxASurface> mSurface;
  83   gfxIntSize mSize;
  84   nsExpirationState mExpirationState;
  85 #ifdef DEBUG
  86   gfxASurface::gfxSurfaceType mType;
  87 #endif
  88 };
  89
  90 #endif /* GFX_CACHED_TEMP_SURFACE_H */