SkXfermode.h revision 86fc266eda887920e3dd104bee8121ae19729cf5 
1
2/*
3 * Copyright 2006 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 SkXfermode_DEFINED
11#define SkXfermode_DEFINED
12
13#include "SkFlattenable.h"
14#include "SkColor.h"
15
16class GrContext;
17class GrEffectRef;
18class GrTexture;
19class SkString;
20
21/** \class SkXfermode
22
23    SkXfermode is the base class for objects that are called to implement custom
24    "transfer-modes" in the drawing pipeline. The static function Create(Modes)
25    can be called to return an instance of any of the predefined subclasses as
26    specified in the Modes enum. When an SkXfermode is assigned to an SkPaint,
27    then objects drawn with that paint have the xfermode applied.
28*/
29class SK_API SkXfermode : public SkFlattenable {
30public:
31    SK_DECLARE_INST_COUNT(SkXfermode)
32
33    SkXfermode() {}
34
35    virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
36                        const SkAlpha aa[]) const;
37    virtual void xfer16(uint16_t dst[], const SkPMColor src[], int count,
38                        const SkAlpha aa[]) const;
39    virtual void xfer4444(uint16_t dst[], const SkPMColor src[], int count,
40                          const SkAlpha aa[]) const;
41    virtual void xferA8(SkAlpha dst[], const SkPMColor src[], int count,
42                        const SkAlpha aa[]) const;
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) const;
77
78    /**
79     *  The same as calling xfermode->asCoeff(..), except that this also checks
80     *  if the xfermode is NULL, and if so, treats it as kSrcOver_Mode.
81     */
82    static bool AsCoeff(const 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        The modes are ordered by those that can be expressed as a pair of Coeffs, followed by those
92        that aren't Coeffs but have separable r,g,b computations, and finally
93        those that are not separable.
94     */
95    enum Mode {
96        kClear_Mode,    //!< [0, 0]
97        kSrc_Mode,      //!< [Sa, Sc]
98        kDst_Mode,      //!< [Da, Dc]
99        kSrcOver_Mode,  //!< [Sa + Da - Sa*Da, Rc = Sc + (1 - Sa)*Dc]
100        kDstOver_Mode,  //!< [Sa + Da - Sa*Da, Rc = Dc + (1 - Da)*Sc]
101        kSrcIn_Mode,    //!< [Sa * Da, Sc * Da]
102        kDstIn_Mode,    //!< [Sa * Da, Sa * Dc]
103        kSrcOut_Mode,   //!< [Sa * (1 - Da), Sc * (1 - Da)]
104        kDstOut_Mode,   //!< [Da * (1 - Sa), Dc * (1 - Sa)]
105        kSrcATop_Mode,  //!< [Da, Sc * Da + (1 - Sa) * Dc]
106        kDstATop_Mode,  //!< [Sa, Sa * Dc + Sc * (1 - Da)]
107        kXor_Mode,      //!< [Sa + Da - 2 * Sa * Da, Sc * (1 - Da) + (1 - Sa) * Dc]
108        kPlus_Mode,     //!< [Sa + Da, Sc + Dc]
109        kModulate_Mode, // multiplies all components (= alpha and color)
110
111        // Following blend modes are defined in the CSS Compositing standard:
112        // https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html#blending
113        kScreen_Mode,
114        kLastCoeffMode = kScreen_Mode,
115
116        kOverlay_Mode,
117        kDarken_Mode,
118        kLighten_Mode,
119        kColorDodge_Mode,
120        kColorBurn_Mode,
121        kHardLight_Mode,
122        kSoftLight_Mode,
123        kDifference_Mode,
124        kExclusion_Mode,
125        kMultiply_Mode,
126        kLastSeparableMode = kMultiply_Mode,
127
128        kHue_Mode,
129        kSaturation_Mode,
130        kColor_Mode,
131        kLuminosity_Mode,
132        kLastMode = kLuminosity_Mode
133    };
134
135    /**
136     * Gets the name of the Mode as a string.
137     */
138    static const char* ModeName(Mode);
139
140    /**
141     *  If the xfermode is one of the modes in the Mode enum, then asMode()
142     *  returns true and sets (if not null) mode accordingly. Otherwise it
143     *  returns false and ignores the mode parameter.
144     */
145    virtual bool asMode(Mode* mode) const;
146
147    /**
148     *  The same as calling xfermode->asMode(mode), except that this also checks
149     *  if the xfermode is NULL, and if so, treats it as kSrcOver_Mode.
150     */
151    static bool AsMode(const SkXfermode*, Mode* mode);
152
153    /**
154     *  Returns true if the xfermode claims to be the specified Mode. This works
155     *  correctly even if the xfermode is NULL (which equates to kSrcOver.) Thus
156     *  you can say this without checking for a null...
157     *
158     *  If (SkXfermode::IsMode(paint.getXfermode(),
159     *                         SkXfermode::kDstOver_Mode)) {
160     *      ...
161     *  }
162     */
163    static bool IsMode(const SkXfermode* xfer, Mode mode);
164
165    /** Return an SkXfermode object for the specified mode.
166     */
167    static SkXfermode* Create(Mode mode);
168
169    /** Return a function pointer to a routine that applies the specified
170        porter-duff transfer mode.
171     */
172    static SkXfermodeProc GetProc(Mode mode);
173
174    /** Return a function pointer to a routine that applies the specified
175        porter-duff transfer mode and srcColor to a 16bit device color. Note,
176        if the mode+srcColor might return a non-opaque color, then there is not
177        16bit proc, and this will return NULL.
178      */
179    static SkXfermodeProc16 GetProc16(Mode mode, SkColor srcColor);
180
181    /**
182     *  If the specified mode can be represented by a pair of Coeff, then return
183     *  true and set (if not NULL) the corresponding coeffs. If the mode is
184     *  not representable as a pair of Coeffs, return false and ignore the
185     *  src and dst parameters.
186     */
187    static bool ModeAsCoeff(Mode mode, Coeff* src, Coeff* dst);
188
189    // DEPRECATED: call AsMode(...)
190    static bool IsMode(const SkXfermode* xfer, Mode* mode) {
191        return AsMode(xfer, mode);
192    }
193
194    /** A subclass may implement this factory function to work with the GPU backend. It is legal
195        to call this with all but the context param NULL to simply test the return value. effect,
196        src, and dst must all be NULL or all non-NULL. If effect is non-NULL then the xfermode may
197        optionally allocate an effect to return and the caller as *effect. The caller will install
198        it and own a ref to it. Since the xfermode may or may not assign *effect, the caller should
199        set *effect to NULL beforehand. If the function returns true and *effect is NULL then the
200        src and dst coeffs will be applied to the draw. When *effect is non-NULL the coeffs are
201        ignored. background specifies the texture to use as the background for compositing, and
202        should be accessed in the effect's fragment shader. If NULL, the effect should request
203        access to destination color (setWillReadDstColor()), and use that in the fragment shader
204        (builder->dstColor()).
205     */
206    virtual bool asNewEffectOrCoeff(GrContext*,
207                                    GrEffectRef** effect,
208                                    Coeff* src,
209                                    Coeff* dst,
210                                    GrTexture* background = NULL) const;
211
212    /**
213     *  The same as calling xfermode->asNewEffect(...), except that this also checks if the xfermode
214     *  is NULL, and if so, treats it as kSrcOver_Mode.
215     */
216    static bool AsNewEffectOrCoeff(SkXfermode*,
217                                   GrContext*,
218                                   GrEffectRef** effect,
219                                   Coeff* src,
220                                   Coeff* dst,
221                                   GrTexture* background = NULL);
222
223    SkDEVCODE(virtual void toString(SkString* str) const = 0;)
224    SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
225protected:
226    SkXfermode(SkFlattenableReadBuffer& rb) : SkFlattenable(rb) {}
227
228    /** The default implementation of xfer32/xfer16/xferA8 in turn call this
229        method, 1 color at a time (upscaled to a SkPMColor). The default
230        implmentation of this method just returns dst. If performance is
231        important, your subclass should override xfer32/xfer16/xferA8 directly.
232
233        This method will not be called directly by the client, so it need not
234        be implemented if your subclass has overridden xfer32/xfer16/xferA8
235    */
236    virtual SkPMColor xferColor(SkPMColor src, SkPMColor dst) const;
237
238private:
239    enum {
240        kModeCount = kLastMode + 1
241    };
242    typedef SkFlattenable INHERITED;
243};
244
245///////////////////////////////////////////////////////////////////////////////
246
247/** \class SkProcXfermode
248
249    SkProcXfermode is a xfermode that applies the specified proc to its colors.
250    This class is not exported to java.
251*/
252class SkProcXfermode : public SkXfermode {
253public:
254    SkProcXfermode(SkXfermodeProc proc) : fProc(proc) {}
255
256    // overrides from SkXfermode
257    virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
258                        const SkAlpha aa[]) const SK_OVERRIDE;
259    virtual void xfer16(uint16_t dst[], const SkPMColor src[], int count,
260                        const SkAlpha aa[]) const SK_OVERRIDE;
261    virtual void xfer4444(uint16_t dst[], const SkPMColor src[], int count,
262                          const SkAlpha aa[]) const SK_OVERRIDE;
263    virtual void xferA8(SkAlpha dst[], const SkPMColor src[], int count,
264                        const SkAlpha aa[]) const SK_OVERRIDE;
265
266    SK_DEVELOPER_TO_STRING()
267    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkProcXfermode)
268
269protected:
270    SkProcXfermode(SkFlattenableReadBuffer&);
271    virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
272
273    // allow subclasses to update this after we unflatten
274    void setProc(SkXfermodeProc proc) {
275        fProc = proc;
276    }
277
278private:
279    SkXfermodeProc  fProc;
280
281    typedef SkXfermode INHERITED;
282};
283
284#endif
285