SkDrawLooper.h revision 9efd9a048aebaa6681afb76b18e1a7dd642078d3 
1
2/*
3 * Copyright 2011 The Android Open Source Project
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9
10#ifndef SkDrawLooper_DEFINED
11#define SkDrawLooper_DEFINED
12
13#include "SkFlattenable.h"
14
15class SkCanvas;
16class SkPaint;
17
18/** \class SkDrawLooper
19    Subclasses of SkDrawLooper can be attached to a SkPaint. Where they are,
20    and something is drawn to a canvas with that paint, the looper subclass will
21    be called, allowing it to modify the canvas and/or paint for that draw call.
22    More than that, via the next() method, the looper can modify the draw to be
23    invoked multiple times (hence the name loop-er), allow it to perform effects
24    like shadows or frame/fills, that require more than one pass.
25*/
26class SK_API SkDrawLooper : public SkFlattenable {
27public:
28    /**
29     *  Called right before something is being drawn. This will be followed by
30     *  calls to next() until next() returns false.
31     */
32    virtual void init(SkCanvas*) = 0;
33
34    /**
35     *  Called in a loop (after init()). Each time true is returned, the object
36     *  is drawn (possibly with a modified canvas and/or paint). When false is
37     *  finally returned, drawing for the object stops.
38     *
39     *  On each call, the paint will be in its original state, but the canvas
40     *  will be as it was following the previous call to next() or init().
41     *
42     *  The implementation must ensure that, when next() finally returns false,
43     *  that the canvas has been restored to the state it was initially, before
44     *  init() was first called.
45     */
46    virtual bool next(SkCanvas*, SkPaint* paint) = 0;
47
48    /**
49     * The fast bounds functions are used to enable the paint to be culled early
50     * in the drawing pipeline. If a subclass can support this feature it must
51     * return true for the canComputeFastBounds() function.  If that function
52     * returns false then computeFastBounds behavior is undefined otherwise it
53     * is expected to have the following behavior. Given the parent paint and
54     * the parent's bounding rect the subclass must fill in and return the
55     * storage rect, where the storage rect is with the union of the src rect
56     * and the looper's bounding rect.
57     */
58    virtual bool canComputeFastBounds(const SkPaint& paint);
59    virtual void computeFastBounds(const SkPaint& paint,
60                                   const SkRect& src, SkRect* dst);
61
62protected:
63    SkDrawLooper() {}
64    SkDrawLooper(SkFlattenableReadBuffer& buffer) : INHERITED(buffer) {}
65
66private:
67    typedef SkFlattenable INHERITED;
68};
69
70#endif
71