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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 "SkBlurTypes.h"
14 #include "SkFlattenable.h"
15 #include "SkPoint.h"
16 #include "SkColor.h"
17 
18 class  SkArenaAlloc;
19 class  SkCanvas;
20 class  SkColorSpaceXformer;
21 class  SkPaint;
22 struct SkRect;
23 class  SkString;
24 
25 /** \class SkDrawLooper
26     Subclasses of SkDrawLooper can be attached to a SkPaint. Where they are,
27     and something is drawn to a canvas with that paint, the looper subclass will
28     be called, allowing it to modify the canvas and/or paint for that draw call.
29     More than that, via the next() method, the looper can modify the draw to be
30     invoked multiple times (hence the name loop-er), allow it to perform effects
31     like shadows or frame/fills, that require more than one pass.
32 */
33 class SK_API SkDrawLooper : public SkFlattenable {
34 public:
35     /**
36      *  Holds state during a draw. Users call next() until it returns false.
37      *
38      *  Subclasses of SkDrawLooper should create a subclass of this object to
39      *  hold state specific to their subclass.
40      */
41     class SK_API Context : ::SkNoncopyable {
42     public:
Context()43         Context() {}
~Context()44         virtual ~Context() {}
45 
46         /**
47          *  Called in a loop on objects returned by SkDrawLooper::createContext().
48          *  Each time true is returned, the object is drawn (possibly with a modified
49          *  canvas and/or paint). When false is finally returned, drawing for the object
50          *  stops.
51          *
52          *  On each call, the paint will be in its original state, but the
53          *  canvas will be as it was following the previous call to next() or
54          *  createContext().
55          *
56          *  The implementation must ensure that, when next() finally returns
57          *  false, the canvas has been restored to the state it was
58          *  initially, before createContext() was first called.
59          */
60         virtual bool next(SkCanvas* canvas, SkPaint* paint) = 0;
61     };
62 
63     /**
64      *  Called right before something is being drawn. Returns a Context
65      *  whose next() method should be called until it returns false.
66      */
67     virtual Context* makeContext(SkCanvas*, SkArenaAlloc*) const = 0;
68 
69     /**
70      * The fast bounds functions are used to enable the paint to be culled early
71      * in the drawing pipeline. If a subclass can support this feature it must
72      * return true for the canComputeFastBounds() function.  If that function
73      * returns false then computeFastBounds behavior is undefined otherwise it
74      * is expected to have the following behavior. Given the parent paint and
75      * the parent's bounding rect the subclass must fill in and return the
76      * storage rect, where the storage rect is with the union of the src rect
77      * and the looper's bounding rect.
78      */
79     bool canComputeFastBounds(const SkPaint& paint) const;
80     void computeFastBounds(const SkPaint& paint, const SkRect& src, SkRect* dst) const;
81 
82     struct BlurShadowRec {
83         SkScalar        fSigma;
84         SkVector        fOffset;
85         SkColor         fColor;
86         SkBlurStyle     fStyle;
87         SkBlurQuality   fQuality;
88     };
89     /**
90      *  If this looper can be interpreted as having two layers, such that
91      *      1. The first layer (bottom most) just has a blur and translate
92      *      2. The second layer has no modifications to either paint or canvas
93      *      3. No other layers.
94      *  then return true, and if not null, fill out the BlurShadowRec).
95      *
96      *  If any of the above are not met, return false and ignore the BlurShadowRec parameter.
97      */
98     virtual bool asABlurShadow(BlurShadowRec*) const;
99 
100     SK_TO_STRING_PUREVIRT()
SK_DEFINE_FLATTENABLE_TYPE(SkDrawLooper)101     SK_DEFINE_FLATTENABLE_TYPE(SkDrawLooper)
102 
103 protected:
104     sk_sp<SkDrawLooper> makeColorSpace(SkColorSpaceXformer* xformer) const {
105         return this->onMakeColorSpace(xformer);
106     }
107     virtual sk_sp<SkDrawLooper> onMakeColorSpace(SkColorSpaceXformer*) const = 0;
108 
SkDrawLooper()109     SkDrawLooper() {}
110 
111 private:
112     friend class SkColorSpaceXformer;
113 
114     typedef SkFlattenable INHERITED;
115 };
116 
117 #endif
118