1/*
2 * Copyright 2006 The Android Open Source Project
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8#ifndef SkColorFilter_DEFINED
9#define SkColorFilter_DEFINED
10
11#include "SkColor.h"
12#include "SkFlattenable.h"
13#include "SkXfermode.h"
14
15class GrContext;
16class GrFragmentProcessor;
17class SkBitmap;
18
19/**
20 *  ColorFilters are optional objects in the drawing pipeline. When present in
21 *  a paint, they are called with the "src" colors, and return new colors, which
22 *  are then passed onto the next stage (either ImageFilter or Xfermode).
23 *
24 *  All subclasses are required to be reentrant-safe : it must be legal to share
25 *  the same instance between several threads.
26 */
27class SK_API SkColorFilter : public SkFlattenable {
28public:
29    /**
30     *  If the filter can be represented by a source color plus Mode, this
31     *  returns true, and sets (if not NULL) the color and mode appropriately.
32     *  If not, this returns false and ignores the parameters.
33     */
34    virtual bool asColorMode(SkColor* color, SkXfermode::Mode* mode) const;
35
36    /**
37     *  If the filter can be represented by a 5x4 matrix, this
38     *  returns true, and sets the matrix appropriately.
39     *  If not, this returns false and ignores the parameter.
40     */
41    virtual bool asColorMatrix(SkScalar matrix[20]) const;
42
43    /**
44     *  If the filter can be represented by per-component table, return true,
45     *  and if table is not null, copy the bitmap containing the table into it.
46     *
47     *  The table bitmap will be in SkBitmap::kA8_Config. Each row corresponding
48     *  to each component in ARGB order. e.g. row[0] == alpha, row[1] == red,
49     *  etc. To transform a color, you (logically) perform the following:
50     *
51     *      a' = *table.getAddr8(a, 0);
52     *      r' = *table.getAddr8(r, 1);
53     *      g' = *table.getAddr8(g, 2);
54     *      b' = *table.getAddr8(b, 3);
55     *
56     *  The original component value is the horizontal index for a given row,
57     *  and the stored value at that index is the new value for that component.
58     */
59    virtual bool asComponentTable(SkBitmap* table) const;
60
61    /** Called with a scanline of colors, as if there was a shader installed.
62        The implementation writes out its filtered version into result[].
63        Note: shader and result may be the same buffer.
64        @param src      array of colors, possibly generated by a shader
65        @param count    the number of entries in the src[] and result[] arrays
66        @param result   written by the filter
67    */
68    virtual void filterSpan(const SkPMColor src[], int count, SkPMColor result[]) const = 0;
69
70    virtual void filterSpan4f(const SkPM4f src[], int count, SkPM4f result[]) const;
71
72    enum Flags {
73        /** If set the filter methods will not change the alpha channel of the colors.
74        */
75        kAlphaUnchanged_Flag = 1 << 0,
76    };
77
78    /** Returns the flags for this filter. Override in subclasses to return custom flags.
79    */
80    virtual uint32_t getFlags() const { return 0; }
81
82    /**
83     *  If this subclass can optimally createa composition with the inner filter, return it as
84     *  a new filter (which the caller must unref() when it is done). If no such optimization
85     *  is known, return NULL.
86     *
87     *  e.g. result(color) == this_filter(inner(color))
88     */
89    virtual SkColorFilter* newComposed(const SkColorFilter* /*inner*/) const { return NULL; }
90
91    /**
92     *  Apply this colorfilter to the specified SkColor. This routine handles
93     *  converting to SkPMColor, calling the filter, and then converting back
94     *  to SkColor. This method is not virtual, but will call filterSpan()
95     *   which is virtual.
96     */
97    SkColor filterColor(SkColor) const;
98
99    /**
100     *  Filters a single color.
101     */
102    SkColor4f filterColor4f(const SkColor4f&) const;
103
104    /** Create a colorfilter that uses the specified color and mode.
105        If the Mode is DST, this function will return NULL (since that
106        mode will have no effect on the result).
107        @param c    The source color used with the specified mode
108        @param mode The xfermode mode that is applied to each color in
109                        the colorfilter's filterSpan[16,32] methods
110        @return colorfilter object that applies the src color and mode,
111                    or NULL if the mode will have no effect.
112    */
113    static SkColorFilter* CreateModeFilter(SkColor c, SkXfermode::Mode mode);
114
115    /** Construct a colorfilter whose effect is to first apply the inner filter and then apply
116     *  the outer filter to the result of the inner's.
117     *  The reference counts for outer and inner are incremented.
118     *
119     *  Due to internal limits, it is possible that this will return NULL, so the caller must
120     *  always check.
121     */
122    static SkColorFilter* CreateComposeFilter(SkColorFilter* outer, SkColorFilter* inner);
123
124    /** Construct a color filter that transforms a color by a 4x5 matrix. The matrix is in row-
125     *  major order and the translation column is specified in unnormalized, 0...255, space.
126     */
127    static SkColorFilter* CreateMatrixFilterRowMajor255(const SkScalar array[20]);
128
129    /**
130     *  A subclass may implement this factory function to work with the GPU backend. It returns
131     *  a GrFragmentProcessor that implemets the color filter in GPU shader code.
132     *
133     *  The fragment processor receives a premultiplied input color and produces a premultiplied
134     *  output color.
135     *
136     *  A null return indicates that the color filter isn't implemented for the GPU backend.
137     */
138    virtual const GrFragmentProcessor* asFragmentProcessor(GrContext*) const {
139        return nullptr;
140    }
141
142    bool affectsTransparentBlack() const {
143        return this->filterColor(0) != 0;
144    }
145
146    SK_TO_STRING_PUREVIRT()
147
148    SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
149    SK_DEFINE_FLATTENABLE_TYPE(SkColorFilter)
150
151protected:
152    SkColorFilter() {}
153
154private:
155    /*
156     *  Returns 1 if this is a single filter (not a composition of other filters), otherwise it
157     *  reutrns the number of leaf-node filters in a composition. This should be the same value
158     *  as the number of GrFragmentProcessors returned by asFragmentProcessors's array parameter.
159     *
160     *  e.g. compose(filter, compose(compose(filter, filter), filter)) --> 4
161     */
162    virtual int privateComposedFilterCount() const { return 1; }
163    friend class SkComposeColorFilter;
164
165    typedef SkFlattenable INHERITED;
166};
167
168#endif
169