SkImageFilter.h revision 9c39744a00573b7133fc765b0a9d50a0ceace7b8 
1/*
2 * Copyright 2011 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 SkImageFilter_DEFINED
9#define SkImageFilter_DEFINED
10
11#include "SkFlattenable.h"
12
13class SkBitmap;
14class SkDevice;
15class SkMatrix;
16struct SkIPoint;
17struct SkIRect;
18struct SkRect;
19class GrCustomStage;
20class GrTexture;
21
22/**
23 *  Experimental.
24 *
25 *  Base class for image filters. If one is installed in the paint, then
26 *  all drawing occurs as usual, but it is as if the drawing happened into an
27 *  offscreen (before the xfermode is applied). This offscreen bitmap will
28 *  then be handed to the imagefilter, who in turn creates a new bitmap which
29 *  is what will finally be drawn to the device (using the original xfermode).
30 *
31 *  THIS SIGNATURE IS TEMPORARY
32 *
33 *  There are several weaknesses in this function signature:
34 *  1. Does not expose the destination/target device, so filters that can draw
35 *     directly to it are unable to take advantage of that optimization.
36 *  2. Does not expose a way to create a "compabitible" image (i.e. gpu -> gpu)
37 *  3. As with #1, the filter is unable to "read" the dest (which would be slow)
38 *
39 *  Therefore, we should not create any real dependencies on this API yet -- it
40 *  is being checked in as a check-point so we can explore these and other
41 *  considerations.
42 */
43class SK_API SkImageFilter : public SkFlattenable {
44public:
45    SK_DECLARE_INST_COUNT(SkImageFilter)
46
47    class Proxy {
48    public:
49        virtual ~Proxy() {};
50
51        virtual SkDevice* createDevice(int width, int height) = 0;
52        // returns true if the proxy can handle this filter natively
53        virtual bool canHandleImageFilter(SkImageFilter*) = 0;
54        // returns true if the proxy handled the filter itself. if this returns
55        // false then the filter's code will be called.
56        virtual bool filterImage(SkImageFilter*, const SkBitmap& src,
57                                 const SkMatrix& ctm,
58                                 SkBitmap* result, SkIPoint* offset) = 0;
59    };
60
61    /**
62     *  Request a new (result) image to be created from the src image.
63     *  If the src has no pixels (isNull()) then the request just wants to
64     *  receive the config and width/height of the result.
65     *
66     *  The matrix is the current matrix on the canvas.
67     *
68     *  Offset is the amount to translate the resulting image relative to the
69     *  src when it is drawn.
70     *
71     *  If the result image cannot be created, return false, in which case both
72     *  the result and offset parameters will be ignored by the caller.
73     */
74    bool filterImage(Proxy*, const SkBitmap& src, const SkMatrix& ctm,
75                     SkBitmap* result, SkIPoint* offset);
76
77    /**
78     *  Given the src bounds of an image, this returns the bounds of the result
79     *  image after the filter has been applied.
80     */
81    bool filterBounds(const SkIRect& src, const SkMatrix& ctm, SkIRect* dst);
82
83    /**
84     *  Returns true if the filter can be expressed a single-pass
85     *  GrCustomStage, used to process this filter on the GPU, or false if
86     *  not.
87     *
88     *  If stage is non-NULL, a new GrCustomStage instance is stored
89     *  in it.  The caller assumes ownership of the stage, and it is up to the
90     *  caller to unref it.
91     */
92    virtual bool asNewCustomStage(GrCustomStage** stage, GrTexture*) const;
93
94    /**
95     *  Returns true if the filter can be processed on the GPU.  This is most
96     *  often used for multi-pass effects, where intermediate results must be
97     *  rendered to textures.  For single-pass effects, use asNewCustomStage().
98     *  The default implementation returns false.
99     */
100    virtual bool canFilterImageGPU() const;
101
102    /**
103     *  Process this image filter on the GPU.  texture is the source texture
104     *  for processing, and rect is the effect region to process.  The
105     *  function must allocate a new texture of at least rect width/height
106     *  size, and return it to the caller.  The default implementation returns
107     *  NULL.
108     */
109    virtual GrTexture* onFilterImageGPU(Proxy*, GrTexture* texture, const SkRect& rect);
110
111protected:
112    SkImageFilter() {}
113    explicit SkImageFilter(SkFlattenableReadBuffer& rb) : INHERITED(rb) {}
114
115    // Default impl returns false
116    virtual bool onFilterImage(Proxy*, const SkBitmap& src, const SkMatrix&,
117                               SkBitmap* result, SkIPoint* offset);
118    // Default impl copies src into dst and returns true
119    virtual bool onFilterBounds(const SkIRect&, const SkMatrix&, SkIRect*);
120
121private:
122    typedef SkFlattenable INHERITED;
123};
124
125#endif
126