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      1 /*
      2  * Copyright 2012 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #ifndef SkSurface_Base_DEFINED
      9 #define SkSurface_Base_DEFINED
     10 
     11 #include "SkSurface.h"
     12 #include "SkCanvas.h"
     13 
     14 class SkSurface_Base : public SkSurface {
     15 public:
     16     SkSurface_Base(int width, int height);
     17     explicit SkSurface_Base(const SkImageInfo&);
     18     virtual ~SkSurface_Base();
     19 
     20     /**
     21      *  Allocate a canvas that will draw into this surface. We will cache this
     22      *  canvas, to return the same object to the caller multiple times. We
     23      *  take ownership, and will call unref() on the canvas when we go out of
     24      *  scope.
     25      */
     26     virtual SkCanvas* onNewCanvas() = 0;
     27 
     28     virtual SkSurface* onNewSurface(const SkImageInfo&) = 0;
     29 
     30     /**
     31      *  Allocate an SkImage that represents the current contents of the surface.
     32      *  This needs to be able to outlive the surface itself (if need be), and
     33      *  must faithfully represent the current contents, even if the surface
     34      *  is chaged after this calle (e.g. it is drawn to via its canvas).
     35      */
     36     virtual SkImage* onNewImageSnapshot() = 0;
     37 
     38     /**
     39      *  Default implementation:
     40      *
     41      *  image = this->newImageSnapshot();
     42      *  if (image) {
     43      *      image->draw(canvas, ...);
     44      *      image->unref();
     45      *  }
     46      */
     47     virtual void onDraw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*);
     48 
     49     /**
     50      * Called as a performance hint when the Surface is allowed to make it's contents
     51      * undefined.
     52      */
     53     virtual void onDiscard() {}
     54 
     55     /**
     56      *  If the surface is about to change, we call this so that our subclass
     57      *  can optionally fork their backend (copy-on-write) in case it was
     58      *  being shared with the cachedImage.
     59      */
     60     virtual void onCopyOnWrite(ContentChangeMode) = 0;
     61 
     62     inline SkCanvas* getCachedCanvas();
     63     inline SkImage* getCachedImage();
     64 
     65     // called by SkSurface to compute a new genID
     66     uint32_t newGenerationID();
     67 
     68 private:
     69     SkCanvas*   fCachedCanvas;
     70     SkImage*    fCachedImage;
     71 
     72     void aboutToDraw(ContentChangeMode mode);
     73     friend class SkCanvas;
     74     friend class SkSurface;
     75 
     76     typedef SkSurface INHERITED;
     77 };
     78 
     79 SkCanvas* SkSurface_Base::getCachedCanvas() {
     80     if (NULL == fCachedCanvas) {
     81         fCachedCanvas = this->onNewCanvas();
     82         if (NULL != fCachedCanvas) {
     83             fCachedCanvas->setSurfaceBase(this);
     84         }
     85     }
     86     return fCachedCanvas;
     87 }
     88 
     89 SkImage* SkSurface_Base::getCachedImage() {
     90     if (NULL == fCachedImage) {
     91         fCachedImage = this->onNewImageSnapshot();
     92         SkASSERT(!fCachedCanvas || fCachedCanvas->getSurfaceBase() == this);
     93     }
     94     return fCachedImage;
     95 }
     96 
     97 #endif
     98