1/*
2 * Copyright 2014 Google Inc.
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 GrFragmentProcessor_DEFINED
9#define GrFragmentProcessor_DEFINED
10
11#include "GrProcessor.h"
12
13class GrCoordTransform;
14class GrGLSLCaps;
15class GrGLSLFragmentProcessor;
16class GrInvariantOutput;
17class GrProcessorKeyBuilder;
18
19/** Provides custom fragment shader code. Fragment processors receive an input color (vec4f) and
20    produce an output color. They may reference textures and uniforms. They may use
21    GrCoordTransforms to receive a transformation of the local coordinates that map from local space
22    to the fragment being processed.
23 */
24class GrFragmentProcessor : public GrProcessor {
25public:
26    /**
27    *  In many instances (e.g. SkShader::asFragmentProcessor() implementations) it is desirable to
28    *  only consider the input color's alpha. However, there is a competing desire to have reusable
29    *  GrFragmentProcessor subclasses that can be used in other scenarios where the entire input
30    *  color is considered. This function exists to filter the input color and pass it to a FP. It
31    *  does so by returning a parent FP that multiplies the passed in FPs output by the parent's
32    *  input alpha. The passed in FP will not receive an input color.
33    */
34    static const GrFragmentProcessor* MulOutputByInputAlpha(const GrFragmentProcessor*);
35
36    /**
37     *  Similar to the above but it modulates the output r,g,b of the child processor by the input
38     *  rgb and then multiplies all the components by the input alpha. This effectively modulates
39     *  the child processor's premul color by a unpremul'ed input and produces a premul output
40     */
41    static const GrFragmentProcessor* MulOutputByInputUnpremulColor(const GrFragmentProcessor*);
42
43    /**
44     *  Returns a parent fragment processor that adopts the passed fragment processor as a child.
45     *  The parent will ignore its input color and instead feed the passed in color as input to the
46     *  child.
47     */
48    static const GrFragmentProcessor* OverrideInput(const GrFragmentProcessor*, GrColor);
49
50    /**
51     * Returns a fragment processor that runs the passed in array of fragment processors in a
52     * series. The original input is passed to the first, the first's output is passed to the
53     * second, etc. The output of the returned processor is the output of the last processor of the
54     * series.
55     */
56    static const GrFragmentProcessor* RunInSeries(const GrFragmentProcessor*[], int cnt);
57
58    GrFragmentProcessor()
59        : INHERITED()
60        , fUsesLocalCoords(false)
61        , fNumTexturesExclChildren(0)
62        , fNumTransformsExclChildren(0) {}
63
64    ~GrFragmentProcessor() override;
65
66    GrGLSLFragmentProcessor* createGLSLInstance() const;
67
68    void getGLSLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const {
69        this->onGetGLSLProcessorKey(caps, b);
70        for (int i = 0; i < fChildProcessors.count(); ++i) {
71            fChildProcessors[i]->getGLSLProcessorKey(caps, b);
72        }
73    }
74
75    int numTexturesExclChildren() const { return fNumTexturesExclChildren; }
76
77    int numTransformsExclChildren() const { return fNumTransformsExclChildren; }
78
79    int numTransforms() const { return fCoordTransforms.count(); }
80
81    /** Returns the coordinate transformation at index. index must be valid according to
82        numTransforms(). */
83    const GrCoordTransform& coordTransform(int index) const { return *fCoordTransforms[index]; }
84
85    const SkTArray<const GrCoordTransform*, true>& coordTransforms() const {
86        return fCoordTransforms;
87    }
88
89    void gatherCoordTransforms(SkTArray<const GrCoordTransform*, true>* outTransforms) const {
90        if (!fCoordTransforms.empty()) {
91            outTransforms->push_back_n(fCoordTransforms.count(), fCoordTransforms.begin());
92        }
93    }
94
95    int numChildProcessors() const { return fChildProcessors.count(); }
96
97    const GrFragmentProcessor& childProcessor(int index) const { return *fChildProcessors[index]; }
98
99    /** Do any of the coordtransforms for this processor require local coords? */
100    bool usesLocalCoords() const { return fUsesLocalCoords; }
101
102    /** Returns true if this and other processor conservatively draw identically. It can only return
103        true when the two processor are of the same subclass (i.e. they return the same object from
104        from getFactory()).
105
106        A return value of true from isEqual() should not be used to test whether the processor would
107        generate the same shader code. To test for identical code generation use getGLSLProcessorKey
108     */
109    bool isEqual(const GrFragmentProcessor& that, bool ignoreCoordTransforms) const;
110
111    /**
112     * This function is used to perform optimizations. When called the invarientOuput param
113     * indicate whether the input components to this processor in the FS will have known values.
114     * In inout the validFlags member is a bitfield of GrColorComponentFlags. The isSingleComponent
115     * member indicates whether the input will be 1 or 4 bytes. The function updates the members of
116     * inout to indicate known values of its output. A component of the color member only has
117     * meaning if the corresponding bit in validFlags is set.
118     */
119    void computeInvariantOutput(GrInvariantOutput* inout) const {
120        this->onComputeInvariantOutput(inout);
121    }
122
123protected:
124    void addTextureAccess(const GrTextureAccess* textureAccess) override;
125
126    /**
127     * Fragment Processor subclasses call this from their constructor to register coordinate
128     * transformations. Coord transforms provide a mechanism for a processor to receive coordinates
129     * in their FS code. The matrix expresses a transformation from local space. For a given
130     * fragment the matrix will be applied to the local coordinate that maps to the fragment.
131     *
132     * When the transformation has perspective, the transformed coordinates will have
133     * 3 components. Otherwise they'll have 2.
134     *
135     * This must only be called from the constructor because GrProcessors are immutable. The
136     * processor subclass manages the lifetime of the transformations (this function only stores a
137     * pointer). The GrCoordTransform is typically a member field of the GrProcessor subclass.
138     *
139     * A processor subclass that has multiple methods of construction should always add its coord
140     * transforms in a consistent order. The non-virtual implementation of isEqual() automatically
141     * compares transforms and will assume they line up across the two processor instances.
142     */
143    void addCoordTransform(const GrCoordTransform*);
144
145    /**
146     * FragmentProcessor subclasses call this from their constructor to register any child
147     * FragmentProcessors they have. This must be called AFTER all texture accesses and coord
148     * transforms have been added.
149     * This is for processors whose shader code will be composed of nested processors whose output
150     * colors will be combined somehow to produce its output color.  Registering these child
151     * processors will allow the ProgramBuilder to automatically handle their transformed coords and
152     * texture accesses and mangle their uniform and output color names.
153     */
154    int registerChildProcessor(const GrFragmentProcessor* child);
155
156    /**
157     * Subclass implements this to support getConstantColorComponents(...).
158     *
159     * Note: it's up to the subclass implementation to do any recursive call to compute the child
160     * procs' output invariants; computeInvariantOutput will not be recursive.
161     */
162    virtual void onComputeInvariantOutput(GrInvariantOutput* inout) const = 0;
163
164private:
165    void notifyRefCntIsZero() const final;
166
167    /** Returns a new instance of the appropriate *GL* implementation class
168        for the given GrFragmentProcessor; caller is responsible for deleting
169        the object. */
170    virtual GrGLSLFragmentProcessor* onCreateGLSLInstance() const = 0;
171
172    /** Implemented using GLFragmentProcessor::GenKey as described in this class's comment. */
173    virtual void onGetGLSLProcessorKey(const GrGLSLCaps& caps,
174                                       GrProcessorKeyBuilder* b) const = 0;
175
176    /**
177     * Subclass implements this to support isEqual(). It will only be called if it is known that
178     * the two processors are of the same subclass (i.e. they return the same object from
179     * getFactory()). The processor subclass should not compare its coord transforms as that will
180     * be performed automatically in the non-virtual isEqual().
181     */
182    virtual bool onIsEqual(const GrFragmentProcessor&) const = 0;
183
184    bool hasSameTransforms(const GrFragmentProcessor&) const;
185
186    bool                                            fUsesLocalCoords;
187
188    /**
189     * fCoordTransforms stores the transforms of this proc, followed by all the transforms of this
190     * proc's children. In other words, each proc stores all the transforms of its subtree as if
191     * they were collected using preorder traversal.
192     *
193     * Example:
194     * Suppose we have frag proc A, who has two children B and D. B has a child C, and D has
195     * two children E and F. Suppose procs A, B, C, D, E, F have 1, 2, 1, 1, 3, 2 transforms
196     * respectively. The following shows what the fCoordTransforms array of each proc would contain:
197     *
198     *                                   (A)
199     *                        [a1,b1,b2,c1,d1,e1,e2,e3,f1,f2]
200     *                                  /    \
201     *                                /        \
202     *                            (B)           (D)
203     *                        [b1,b2,c1]   [d1,e1,e2,e3,f1,f2]
204     *                          /             /    \
205     *                        /             /        \
206     *                      (C)          (E)          (F)
207     *                     [c1]      [e1,e2,e3]      [f1,f2]
208     *
209     * The same goes for fTextureAccesses with textures.
210     */
211    SkSTArray<4, const GrCoordTransform*, true>     fCoordTransforms;
212    int                                             fNumTexturesExclChildren;
213    int                                             fNumTransformsExclChildren;
214    SkSTArray<1, const GrFragmentProcessor*, true>  fChildProcessors;
215
216    typedef GrProcessor INHERITED;
217};
218
219#endif
220