SkDrawLooper.h revision 8a1c16ff38322f0210116fa7293eb8817c7e477e 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef SkDrawLooper_DEFINED
18#define SkDrawLooper_DEFINED
19
20#include "SkFlattenable.h"
21
22////////////////// EXPERIMENTAL //////////////////////////
23
24class SkCanvas;
25class SkPaint;
26
27/** \class SkDrawLooper
28    Subclasses of SkDrawLooper can be attached to a SkPaint. Where they are,
29    and something is drawn to a canvas with that paint, the looper subclass will
30    be called, allowing it to modify the canvas and/or paint for that draw call.
31    More than that, via the next() method, the looper can modify the draw to be
32    invoked multiple times (hence the name loop-er), allow it to perform effects
33    like shadows or frame/fills, that require more than one pass.
34*/
35class SkDrawLooper : public SkFlattenable {
36public:
37    /** Called right before something is being drawn to the specified canvas
38        with the specified paint. Subclass that want to modify either parameter
39        can do so now.
40    */
41    virtual void init(SkCanvas*, SkPaint*) {}
42    /** Called in a loop (after init()). Each time true is returned, the object
43        is drawn (possibly with a modified canvas and/or paint). When false is
44        finally returned, drawing for the object stops.
45    */
46    virtual bool next() { return false; }
47    /** Called after the looper has finally returned false from next(), allowing
48        the looper to restore the canvas/paint to their original states.
49        is this required, since the subclass knows when it is done???
50        should we pass the canvas/paint here, and/or to the next call
51        so that subclasses don't need to retain pointers to them during the
52        loop?
53    */
54    virtual void restore() {}
55
56protected:
57    SkDrawLooper() {}
58    SkDrawLooper(SkFlattenableReadBuffer& buffer) : INHERITED(buffer) {}
59
60private:
61    typedef SkFlattenable INHERITED;
62};
63
64#endif
65