SkXfermode.h revision 081560e3abe25c4821b79ca1465f4dbd371c4b5c 
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 GrEffectRef;
17class GrTexture;
18class SkString;
19
20/** \class SkXfermode
21 *
22 *  SkXfermode is the base class for objects that are called to implement custom
23 *  "transfer-modes" in the drawing pipeline. The static function Create(Modes)
24 *  can be called to return an instance of any of the predefined subclasses as
25 *  specified in the Modes enum. When an SkXfermode is assigned to an SkPaint,
26 *  then objects drawn with that paint have the xfermode applied.
27 *
28 *  All subclasses are required to be reentrant-safe : it must be legal to share
29 *  the same instance between several threads.
30 */
31class SK_API SkXfermode : public SkFlattenable {
32public:
33    SK_DECLARE_INST_COUNT(SkXfermode)
34
35    SkXfermode() {}
36
37    virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
38                        const SkAlpha aa[]) const;
39    virtual void xfer16(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    SK_ATTR_DEPRECATED("use 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 params NULL to simply test the return value. If effect is non-NULL
196        then the xfermode may optionally allocate an effect to return and the caller as *effect.
197        The caller will install it and own a ref to it. Since the xfermode may or may not assign
198        *effect, the caller should set *effect to NULL beforehand. background specifies the
199        texture to use as the background for compositing, and should be accessed in the effect's
200        fragment shader. If NULL, the effect should request access to destination color
201        (setWillReadDstColor()), and use that in the fragment shader (builder->dstColor()).
202     */
203    virtual bool asNewEffect(GrEffectRef** effect, GrTexture* background = NULL) const;
204
205    /** Returns true if the xfermode can be expressed as coeffs (src, dst), or as an effect
206        (effect). This helper calls the asCoeff() and asNewEffect() virtuals. If the xfermode is
207        NULL, it is treated as kSrcOver_Mode. It is legal to call this with all params NULL to
208        simply test the return value.  effect, src, and dst must all be NULL or all non-NULL.
209     */
210    static bool AsNewEffectOrCoeff(SkXfermode*,
211                                   GrEffectRef** effect,
212                                   Coeff* src,
213                                   Coeff* dst,
214                                   GrTexture* background = NULL);
215
216    SkDEVCODE(virtual void toString(SkString* str) const = 0;)
217    SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
218    SK_DEFINE_FLATTENABLE_TYPE(SkXfermode)
219
220protected:
221    SkXfermode(SkFlattenableReadBuffer& rb) : SkFlattenable(rb) {}
222
223    /** The default implementation of xfer32/xfer16/xferA8 in turn call this
224        method, 1 color at a time (upscaled to a SkPMColor). The default
225        implmentation of this method just returns dst. If performance is
226        important, your subclass should override xfer32/xfer16/xferA8 directly.
227
228        This method will not be called directly by the client, so it need not
229        be implemented if your subclass has overridden xfer32/xfer16/xferA8
230    */
231    virtual SkPMColor xferColor(SkPMColor src, SkPMColor dst) const;
232
233private:
234    enum {
235        kModeCount = kLastMode + 1
236    };
237
238    friend class SkGraphics;
239    static void Term();
240
241    typedef SkFlattenable INHERITED;
242};
243
244///////////////////////////////////////////////////////////////////////////////
245
246/** \class SkProcXfermode
247
248    SkProcXfermode is a xfermode that applies the specified proc to its colors.
249    This class is not exported to java.
250*/
251class SkProcXfermode : public SkXfermode {
252public:
253    SkProcXfermode(SkXfermodeProc proc) : fProc(proc) {}
254
255    // overrides from SkXfermode
256    virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
257                        const SkAlpha aa[]) const SK_OVERRIDE;
258    virtual void xfer16(uint16_t dst[], const SkPMColor src[], int count,
259                        const SkAlpha aa[]) const SK_OVERRIDE;
260    virtual void xferA8(SkAlpha dst[], const SkPMColor src[], int count,
261                        const SkAlpha aa[]) const SK_OVERRIDE;
262
263    SK_DEVELOPER_TO_STRING()
264    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkProcXfermode)
265
266protected:
267    SkProcXfermode(SkFlattenableReadBuffer&);
268    virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
269
270    // allow subclasses to update this after we unflatten
271    void setProc(SkXfermodeProc proc) {
272        fProc = proc;
273    }
274
275    SkXfermodeProc getProc() const {
276        return fProc;
277    }
278
279private:
280    SkXfermodeProc  fProc;
281
282    typedef SkXfermode INHERITED;
283};
284
285#endif
286