SkXfermode.h revision 43c50c8c77df82c5cffb55cae2d386e59802b88f 
1/*
2 * Copyright (C) 2006 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 SkXfermode_DEFINED
18#define SkXfermode_DEFINED
19
20#include "SkFlattenable.h"
21#include "SkColor.h"
22
23/** \class SkXfermode
24
25    SkXfermode is the base class for objects that are called to implement custom
26    "transfer-modes" in the drawing pipeline. The static function Create(Modes)
27    can be called to return an instance of any of the predefined subclasses as
28    specified in the Modes enum. When an SkXfermode is assigned to an SkPaint,
29    then objects drawn with that paint have the xfermode applied.
30*/
31class SK_API SkXfermode : public SkFlattenable {
32public:
33    SkXfermode() {}
34
35    virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
36                        const SkAlpha aa[]);
37    virtual void xfer16(uint16_t dst[], const SkPMColor src[], int count,
38                        const SkAlpha aa[]);
39    virtual void xfer4444(uint16_t dst[], const SkPMColor src[], int count,
40                          const SkAlpha aa[]);
41    virtual void xferA8(SkAlpha dst[], const SkPMColor src[], int count,
42                        const SkAlpha aa[]);
43
44    /** Enum of possible coefficients to describe some xfermodes
45     */
46    enum Coeff {
47        kZero_Coeff,    /** 0 */
48        kOne_Coeff,     /** 1 */
49        kSC_Coeff,      /** src color */
50        kISC_Coeff,     /** inverse src color (i.e. 1 - sc) */
51        kDC_Coeff,      /** dst color */
52        kIDC_Coeff,     /** inverse dst color (i.e. 1 - dc) */
53        kSA_Coeff,      /** src alpha */
54        kISA_Coeff,     /** inverse src alpha (i.e. 1 - sa) */
55        kDA_Coeff,      /** dst alpha */
56        kIDA_Coeff,     /** inverse dst alpha (i.e. 1 - da) */
57
58        kCoeffCount
59    };
60
61    /** If the xfermode can be expressed as an equation using the coefficients
62        in Coeff, then asCoeff() returns true, and sets (if not null) src and
63        dst accordingly.
64
65            result = src_coeff * src_color + dst_coeff * dst_color;
66
67        As examples, here are some of the porterduff coefficients
68
69        MODE        SRC_COEFF       DST_COEFF
70        clear       zero            zero
71        src         one             zero
72        dst         zero            one
73        srcover     one             isa
74        dstover     ida             one
75     */
76    virtual bool asCoeff(Coeff* src, Coeff* dst);
77
78    /**
79     *  The same as calling xfermode->asCoeff(..), except that this also checks
80     *  if the xfermode is NULL, and if so, treats its as kSrcOver_Mode.
81     */
82    static bool AsCoeff(SkXfermode*, Coeff* src, Coeff* dst);
83
84    /** List of predefined xfermodes.
85        The algebra for the modes uses the following symbols:
86        Sa, Sc  - source alpha and color
87        Da, Dc - destination alpha and color (before compositing)
88        [a, c] - Resulting (alpha, color) values
89        For these equations, the colors are in premultiplied state.
90        If no xfermode is specified, kSrcOver is assumed.
91     */
92    enum Mode {
93        kClear_Mode,    //!< [0, 0]
94        kSrc_Mode,      //!< [Sa, Sc]
95        kDst_Mode,      //!< [Da, Dc]
96        kSrcOver_Mode,  //!< [Sa + Da - Sa*Da, Rc = Sc + (1 - Sa)*Dc]
97        kDstOver_Mode,  //!< [Sa + Da - Sa*Da, Rc = Dc + (1 - Da)*Sc]
98        kSrcIn_Mode,    //!< [Sa * Da, Sc * Da]
99        kDstIn_Mode,    //!< [Sa * Da, Sa * Dc]
100        kSrcOut_Mode,   //!< [Sa * (1 - Da), Sc * (1 - Da)]
101        kDstOut_Mode,   //!< [Da * (1 - Sa), Dc * (1 - Sa)]
102        kSrcATop_Mode,  //!< [Da, Sc * Da + (1 - Sa) * Dc]
103        kDstATop_Mode,  //!< [Sa, Sa * Dc + Sc * (1 - Da)]
104        kXor_Mode,      //!< [Sa + Da - 2 * Sa * Da, Sc * (1 - Da) + (1 - Sa) * Dc]
105
106        // these modes are defined in the SVG Compositing standard
107        // http://www.w3.org/TR/2009/WD-SVGCompositing-20090430/
108        kPlus_Mode,
109        kMultiply_Mode,
110        kScreen_Mode,
111        kOverlay_Mode,
112        kDarken_Mode,
113        kLighten_Mode,
114        kColorDodge_Mode,
115        kColorBurn_Mode,
116        kHardLight_Mode,
117        kSoftLight_Mode,
118        kDifference_Mode,
119        kExclusion_Mode,
120
121        kLastMode = kExclusion_Mode
122    };
123
124    /**
125     *  If the xfermode is one of the modes in the Mode enum, then asMode()
126     *  returns true and sets (if not null) mode accordingly. Otherwise it
127     *  returns false and ignores the mode parameter.
128     */
129    virtual bool asMode(Mode* mode);
130
131    /**
132     *  The same as calling xfermode->asMode(mode), except that this also checks
133     *  if the xfermode is NULL, and if so, treats its as kSrcOver_Mode.
134     */
135    static bool AsMode(SkXfermode*, Mode* mode);
136
137    /** Return an SkXfermode object for the specified mode.
138     */
139    static SkXfermode* Create(Mode mode);
140
141    /** Return a function pointer to a routine that applies the specified
142        porter-duff transfer mode.
143     */
144    static SkXfermodeProc GetProc(Mode mode);
145
146    /** Return a function pointer to a routine that applies the specified
147        porter-duff transfer mode and srcColor to a 16bit device color. Note,
148        if the mode+srcColor might return a non-opaque color, then there is not
149        16bit proc, and this will return NULL.
150      */
151    static SkXfermodeProc16 GetProc16(Mode mode, SkColor srcColor);
152
153    /**
154     *  If the specified mode can be represented by a pair of Coeff, then return
155     *  true and set (if not NULL) the corresponding coeffs. If the mode is
156     *  not representable as a pair of Coeffs, return false and ignore the
157     *  src and dst parameters.
158     */
159    static bool ModeAsCoeff(Mode mode, Coeff* src, Coeff* dst);
160
161    // DEPRECATED: call AsMode(...)
162    static bool IsMode(SkXfermode* xfer, Mode* mode) {
163        return AsMode(xfer, mode);
164    }
165
166protected:
167    SkXfermode(SkFlattenableReadBuffer& rb) : SkFlattenable(rb) {}
168
169    /** The default implementation of xfer32/xfer16/xferA8 in turn call this
170        method, 1 color at a time (upscaled to a SkPMColor). The default
171        implmentation of this method just returns dst. If performance is
172        important, your subclass should override xfer32/xfer16/xferA8 directly.
173
174        This method will not be called directly by the client, so it need not
175        be implemented if your subclass has overridden xfer32/xfer16/xferA8
176    */
177    virtual SkPMColor xferColor(SkPMColor src, SkPMColor dst);
178
179private:
180    enum {
181        kModeCount = kLastMode + 1
182    };
183    typedef SkFlattenable INHERITED;
184};
185
186///////////////////////////////////////////////////////////////////////////////
187
188/** \class SkProcXfermode
189
190    SkProcXfermode is a xfermode that applies the specified proc to its colors.
191    This class is not exported to java.
192*/
193class SkProcXfermode : public SkXfermode {
194public:
195    SkProcXfermode(SkXfermodeProc proc) : fProc(proc) {}
196
197    // overrides from SkXfermode
198    virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
199                        const SkAlpha aa[]);
200    virtual void xfer16(uint16_t dst[], const SkPMColor src[], int count,
201                        const SkAlpha aa[]);
202    virtual void xfer4444(uint16_t dst[], const SkPMColor src[], int count,
203                          const SkAlpha aa[]);
204    virtual void xferA8(SkAlpha dst[], const SkPMColor src[], int count,
205                        const SkAlpha aa[]);
206
207    // overrides from SkFlattenable
208    virtual Factory getFactory() { return CreateProc; }
209    virtual void    flatten(SkFlattenableWriteBuffer&);
210
211protected:
212    SkProcXfermode(SkFlattenableReadBuffer&);
213
214private:
215    SkXfermodeProc  fProc;
216
217    static SkFlattenable* CreateProc(SkFlattenableReadBuffer& buffer) {
218        return SkNEW_ARGS(SkProcXfermode, (buffer)); }
219
220    typedef SkXfermode INHERITED;
221};
222
223#endif
224
225