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1 /*
2  * Copyright 2017 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 GrCCCubicShader_DEFINED
9 #define GrCCCubicShader_DEFINED
10 
11 #include "ccpr/GrCCCoverageProcessor.h"
12 
13 /**
14  * This class renders the coverage of convex closed cubic segments using the techniques outlined in
15  * "Resolution Independent Curve Rendering using Programmable Graphics Hardware" by Charles Loop and
16  * Jim Blinn:
17  *
18  * https://www.microsoft.com/en-us/research/wp-content/uploads/2005/01/p1000-loop.pdf
19  *
20  * The provided curve segments must be convex, monotonic with respect to the vector of their closing
21  * edge [P3 - P0], and must not contain or be near any inflection points or loop intersections.
22  * (Use GrCCGeometry::cubicTo().)
23  */
24 class GrCCCubicShader : public GrCCCoverageProcessor::Shader {
25 public:
26     void emitSetupCode(GrGLSLVertexGeoBuilder*, const char* pts, const char* wind,
27                        const char** outHull4) const override;
28 
29     void onEmitVaryings(GrGLSLVaryingHandler*, GrGLSLVarying::Scope, SkString* code,
30                         const char* position, const char* coverage,
31                         const char* cornerCoverage) override;
32 
33     void onEmitFragmentCode(GrGLSLFPFragmentBuilder*, const char* outputCoverage) const override;
34 
35 private:
36     void calcHullCoverage(SkString* code, const char* klmAndEdge, const char* gradMatrix,
37                           const char* outputCoverage) const;
38 
39     const GrShaderVar fKLMMatrix{"klm_matrix", kFloat3x3_GrSLType};
40     const GrShaderVar fEdgeDistanceEquation{"edge_distance_equation", kFloat3_GrSLType};
41     GrGLSLVarying fKLM_fEdge;
42     GrGLSLVarying fGradMatrix;
43     GrGLSLVarying fCornerCoverage;
44 };
45 
46 #endif
47