1
2/*
3 * Copyright 2011 Google Inc.
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 GrPaint_DEFINED
11#define GrPaint_DEFINED
12
13#include "GrColor.h"
14#include "GrEffectStage.h"
15
16#include "SkXfermode.h"
17
18/**
19 * The paint describes how color and coverage are computed at each pixel by GrContext draw
20 * functions and the how color is blended with the destination pixel.
21 *
22 * The paint allows installation of custom color and coverage stages. New types of stages are
23 * created by subclassing GrEffect.
24 *
25 * The primitive color computation starts with the color specified by setColor(). This color is the
26 * input to the first color stage. Each color stage feeds its output to the next color stage. The
27 * final color stage's output color is input to the color filter specified by
28 * setXfermodeColorFilter which produces the final source color, S.
29 *
30 * Fractional pixel coverage follows a similar flow. The coverage is initially the value specified
31 * by setCoverage(). This is input to the first coverage stage. Coverage stages are chained
32 * together in the same manner as color stages. The output of the last stage is modulated by any
33 * fractional coverage produced by anti-aliasing. This last step produces the final coverage, C.
34 *
35 * setBlendFunc() specifies blending coefficients for S (described above) and D, the initial value
36 * of the destination pixel, labeled Bs and Bd respectively. The final value of the destination
37 * pixel is then D' = (1-C)*D + C*(Bd*D + Bs*S).
38 *
39 * Note that the coverage is applied after the blend. This is why they are computed as distinct
40 * values.
41 *
42 * TODO: Encapsulate setXfermodeColorFilter in a GrEffect and remove from GrPaint.
43 */
44class GrPaint {
45public:
46    GrPaint() { this->reset(); }
47
48    GrPaint(const GrPaint& paint) { *this = paint; }
49
50    ~GrPaint() {}
51
52    /**
53     * Sets the blending coefficients to use to blend the final primitive color with the
54     * destination color. Defaults to kOne for src and kZero for dst (i.e. src mode).
55     */
56    void setBlendFunc(GrBlendCoeff srcCoeff, GrBlendCoeff dstCoeff) {
57        fSrcBlendCoeff = srcCoeff;
58        fDstBlendCoeff = dstCoeff;
59    }
60    GrBlendCoeff getSrcBlendCoeff() const { return fSrcBlendCoeff; }
61    GrBlendCoeff getDstBlendCoeff() const { return fDstBlendCoeff; }
62
63    /**
64     * The initial color of the drawn primitive. Defaults to solid white.
65     */
66    void setColor(GrColor color) { fColor = color; }
67    GrColor getColor() const { return fColor; }
68
69    /**
70     * Applies fractional coverage to the entire drawn primitive. Defaults to 0xff.
71     */
72    void setCoverage(uint8_t coverage) { fCoverage = coverage; }
73    uint8_t getCoverage() const { return fCoverage; }
74
75    /**
76     * Should primitives be anti-aliased or not. Defaults to false.
77     */
78    void setAntiAlias(bool aa) { fAntiAlias = aa; }
79    bool isAntiAlias() const { return fAntiAlias; }
80
81    /**
82     * Should dithering be applied. Defaults to false.
83     */
84    void setDither(bool dither) { fDither = dither; }
85    bool isDither() const { return fDither; }
86
87    /**
88     * Appends an additional color effect to the color computation.
89     */
90    const GrEffectRef* addColorEffect(const GrEffectRef* effect, int attr0 = -1, int attr1 = -1) {
91        SkASSERT(NULL != effect);
92        if (!(*effect)->willUseInputColor()) {
93            fColorStages.reset();
94        }
95        SkNEW_APPEND_TO_TARRAY(&fColorStages, GrEffectStage, (effect, attr0, attr1));
96        return effect;
97    }
98
99    /**
100     * Appends an additional coverage effect to the coverage computation.
101     */
102    const GrEffectRef* addCoverageEffect(const GrEffectRef* effect, int attr0 = -1, int attr1 = -1) {
103        SkASSERT(NULL != effect);
104        if (!(*effect)->willUseInputColor()) {
105            fCoverageStages.reset();
106        }
107        SkNEW_APPEND_TO_TARRAY(&fCoverageStages, GrEffectStage, (effect, attr0, attr1));
108        return effect;
109    }
110
111    /**
112     * Helpers for adding color or coverage effects that sample a texture. The matrix is applied
113     * to the src space position to compute texture coordinates.
114     */
115    void addColorTextureEffect(GrTexture* texture, const SkMatrix& matrix);
116    void addCoverageTextureEffect(GrTexture* texture, const SkMatrix& matrix);
117
118    void addColorTextureEffect(GrTexture* texture,
119                               const SkMatrix& matrix,
120                               const GrTextureParams& params);
121    void addCoverageTextureEffect(GrTexture* texture,
122                                  const SkMatrix& matrix,
123                                  const GrTextureParams& params);
124
125    int numColorStages() const { return fColorStages.count(); }
126    int numCoverageStages() const { return fCoverageStages.count(); }
127    int numTotalStages() const { return this->numColorStages() + this->numCoverageStages(); }
128
129    const GrEffectStage& getColorStage(int s) const { return fColorStages[s]; }
130    const GrEffectStage& getCoverageStage(int s) const { return fCoverageStages[s]; }
131
132    GrPaint& operator=(const GrPaint& paint) {
133        fSrcBlendCoeff = paint.fSrcBlendCoeff;
134        fDstBlendCoeff = paint.fDstBlendCoeff;
135        fAntiAlias = paint.fAntiAlias;
136        fDither = paint.fDither;
137
138        fColor = paint.fColor;
139        fCoverage = paint.fCoverage;
140
141        fColorStages = paint.fColorStages;
142        fCoverageStages = paint.fCoverageStages;
143
144        return *this;
145    }
146
147    /**
148     * Resets the paint to the defaults.
149     */
150    void reset() {
151        this->resetBlend();
152        this->resetOptions();
153        this->resetColor();
154        this->resetCoverage();
155        this->resetStages();
156    }
157
158    /**
159     * Determines whether the drawing with this paint is opaque with respect to both color blending
160     * and fractional coverage. It does not consider whether AA has been enabled on the paint or
161     * not. Depending upon whether multisampling or coverage-based AA is in use, AA may make the
162     * result only apply to the interior of primitives.
163     *
164     */
165    bool isOpaque() const;
166
167    /**
168     * Returns true if isOpaque would return true and the paint represents a solid constant color
169     * draw. If the result is true, constantColor will be updated to contain the constant color.
170     */
171    bool isOpaqueAndConstantColor(GrColor* constantColor) const;
172
173private:
174
175    /**
176     * Helper for isOpaque and isOpaqueAndConstantColor.
177     */
178    bool getOpaqueAndKnownColor(GrColor* solidColor, uint32_t* solidColorKnownComponents) const;
179
180    /**
181     * Called when the source coord system from which geometry is rendered changes. It ensures that
182     * the local coordinates seen by effects remains unchanged. oldToNew gives the transformation
183     * from the previous coord system to the new coord system.
184     */
185    void localCoordChange(const SkMatrix& oldToNew) {
186        for (int i = 0; i < fColorStages.count(); ++i) {
187            fColorStages[i].localCoordChange(oldToNew);
188        }
189        for (int i = 0; i < fCoverageStages.count(); ++i) {
190            fCoverageStages[i].localCoordChange(oldToNew);
191        }
192    }
193
194    bool localCoordChangeInverse(const SkMatrix& newToOld) {
195        SkMatrix oldToNew;
196        bool computed = false;
197        for (int i = 0; i < fColorStages.count(); ++i) {
198            if (!computed && !newToOld.invert(&oldToNew)) {
199                return false;
200            } else {
201                computed = true;
202            }
203            fColorStages[i].localCoordChange(oldToNew);
204        }
205        for (int i = 0; i < fCoverageStages.count(); ++i) {
206            if (!computed && !newToOld.invert(&oldToNew)) {
207                return false;
208            } else {
209                computed = true;
210            }
211            fCoverageStages[i].localCoordChange(oldToNew);
212        }
213        return true;
214    }
215
216    friend class GrContext; // To access above two functions
217
218    SkSTArray<4, GrEffectStage> fColorStages;
219    SkSTArray<2, GrEffectStage> fCoverageStages;
220
221    GrBlendCoeff                fSrcBlendCoeff;
222    GrBlendCoeff                fDstBlendCoeff;
223    bool                        fAntiAlias;
224    bool                        fDither;
225
226    GrColor                     fColor;
227    uint8_t                     fCoverage;
228
229    void resetBlend() {
230        fSrcBlendCoeff = kOne_GrBlendCoeff;
231        fDstBlendCoeff = kZero_GrBlendCoeff;
232    }
233
234    void resetOptions() {
235        fAntiAlias = false;
236        fDither = false;
237    }
238
239    void resetColor() {
240        fColor = GrColorPackRGBA(0xff, 0xff, 0xff, 0xff);
241    }
242
243    void resetCoverage() {
244        fCoverage = 0xff;
245    }
246
247    void resetStages() {
248        fColorStages.reset();
249        fCoverageStages.reset();
250    }
251};
252
253#endif
254