1/*
2 * Copyright 2013 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 GrBezierEffect_DEFINED
9#define GrBezierEffect_DEFINED
10
11#include "include/private/GrTypesPriv.h"
12#include "src/core/SkArenaAlloc.h"
13#include "src/gpu/GrCaps.h"
14#include "src/gpu/GrGeometryProcessor.h"
15#include "src/gpu/GrProcessor.h"
16
17/**
18 * Shader is based off of Loop-Blinn Quadratic GPU Rendering
19 * The output of this effect is a hairline edge for conics.
20 * Conics specified by implicit equation K^2 - LM.
21 * K, L, and M, are the first three values of the vertex attribute,
22 * the fourth value is not used. Distance is calculated using a
23 * first order approximation from the taylor series.
24 * Coverage for AA is max(0, 1-distance).
25 *
26 * Test were also run using a second order distance approximation.
27 * There were two versions of the second order approx. The first version
28 * is of roughly the form:
29 * f(q) = |f(p)| - ||f'(p)||*||q-p|| - ||f''(p)||*||q-p||^2.
30 * The second is similar:
31 * f(q) = |f(p)| + ||f'(p)||*||q-p|| + ||f''(p)||*||q-p||^2.
32 * The exact version of the equations can be found in the paper
33 * "Distance Approximations for Rasterizing Implicit Curves" by Gabriel Taubin
34 *
35 * In both versions we solve the quadratic for ||q-p||.
36 * Version 1:
37 * gFM is magnitude of first partials and gFM2 is magnitude of 2nd partials (as derived from paper)
38 * builder->fsCodeAppend("\t\tedgeAlpha = (sqrt(gFM*gFM+4.0*func*gF2M) - gFM)/(2.0*gF2M);\n");
39 * Version 2:
40 * builder->fsCodeAppend("\t\tedgeAlpha = (gFM - sqrt(gFM*gFM-4.0*func*gF2M))/(2.0*gF2M);\n");
41 *
42 * Also note that 2nd partials of k,l,m are zero
43 *
44 * When comparing the two second order approximations to the first order approximations,
45 * the following results were found. Version 1 tends to underestimate the distances, thus it
46 * basically increases all the error that we were already seeing in the first order
47 * approx. So this version is not the one to use. Version 2 has the opposite effect
48 * and tends to overestimate the distances. This is much closer to what we are
49 * looking for. It is able to render ellipses (even thin ones) without the need to chop.
50 * However, it can not handle thin hyperbolas well and thus would still rely on
51 * chopping to tighten the clipping. Another side effect of the overestimating is
52 * that the curves become much thinner and "ropey". If all that was ever rendered
53 * were "not too thin" curves and ellipses then 2nd order may have an advantage since
54 * only one geometry would need to be rendered. However no benches were run comparing
55 * chopped first order and non chopped 2nd order.
56 */
57class GrGLConicEffect;
58
59class GrConicEffect : public GrGeometryProcessor {
60public:
61 static GrGeometryProcessor* Make(SkArenaAlloc* arena,
62 const SkPMColor4f& color,
63 const SkMatrix& viewMatrix,
64 const GrCaps& caps,
65 const SkMatrix& localMatrix,
66 bool usesLocalCoords,
67 uint8_t coverage = 0xff) {
68 if (!caps.shaderCaps()->shaderDerivativeSupport()) {
69 return nullptr;
70 }
71
72 return arena->make<GrConicEffect>(color, viewMatrix, coverage, localMatrix,
73 usesLocalCoords);
74 }
75
76 ~GrConicEffect() override;
77
78 const char* name() const override { return "Conic"; }
79
80 inline const Attribute& inPosition() const { return kAttributes[0]; }
81 inline const Attribute& inConicCoeffs() const { return kAttributes[1]; }
82 inline bool isAntiAliased() const { return true; }
83 inline bool isFilled() const { return false; }
84 const SkPMColor4f& color() const { return fColor; }
85 const SkMatrix& viewMatrix() const { return fViewMatrix; }
86 const SkMatrix& localMatrix() const { return fLocalMatrix; }
87 bool usesLocalCoords() const { return fUsesLocalCoords; }
88 uint8_t coverageScale() const { return fCoverageScale; }
89
90 void getGLSLProcessorKey(const GrShaderCaps& caps, GrProcessorKeyBuilder* b) const override;
91
92 GrGLSLPrimitiveProcessor* createGLSLInstance(const GrShaderCaps&) const override;
93
94private:
95 friend class ::SkArenaAlloc; // for access to ctor
96
97 GrConicEffect(const SkPMColor4f&, const SkMatrix& viewMatrix, uint8_t coverage,
98 const SkMatrix& localMatrix, bool usesLocalCoords);
99
100 SkPMColor4f fColor;
101 SkMatrix fViewMatrix;
102 SkMatrix fLocalMatrix;
103 bool fUsesLocalCoords;
104 uint8_t fCoverageScale;
105 static constexpr Attribute kAttributes[] = {
106 {"inPosition", kFloat2_GrVertexAttribType, kFloat2_GrSLType},
107 {"inConicCoeffs", kFloat4_GrVertexAttribType, kHalf4_GrSLType}
108 };
109
110 GR_DECLARE_GEOMETRY_PROCESSOR_TEST
111
112 typedef GrGeometryProcessor INHERITED;
113};
114
115///////////////////////////////////////////////////////////////////////////////
116/**
117 * The output of this effect is a hairline edge for quadratics.
118 * Quadratic specified by 0=u^2-v canonical coords. u and v are the first
119 * two components of the vertex attribute. At the three control points that define
120 * the Quadratic, u, v have the values {0,0}, {1/2, 0}, and {1, 1} respectively.
121 * Coverage for AA is min(0, 1-distance). 3rd & 4th cimponent unused.
122 * Requires shader derivative instruction support.
123 */
124class GrGLQuadEffect;
125
126class GrQuadEffect : public GrGeometryProcessor {
127public:
128 static GrGeometryProcessor* Make(SkArenaAlloc* arena,
129 const SkPMColor4f& color,
130 const SkMatrix& viewMatrix,
131 const GrCaps& caps,
132 const SkMatrix& localMatrix,
133 bool usesLocalCoords,
134 uint8_t coverage = 0xff) {
135 if (!caps.shaderCaps()->shaderDerivativeSupport()) {
136 return nullptr;
137 }
138
139 return arena->make<GrQuadEffect>(color, viewMatrix, coverage, localMatrix, usesLocalCoords);
140 }
141
142 ~GrQuadEffect() override;
143
144 const char* name() const override { return "Quad"; }
145
146 inline const Attribute& inPosition() const { return kAttributes[0]; }
147 inline const Attribute& inHairQuadEdge() const { return kAttributes[1]; }
148 inline bool isAntiAliased() const { return true; }
149 inline bool isFilled() const { return false; }
150 const SkPMColor4f& color() const { return fColor; }
151 const SkMatrix& viewMatrix() const { return fViewMatrix; }
152 const SkMatrix& localMatrix() const { return fLocalMatrix; }
153 bool usesLocalCoords() const { return fUsesLocalCoords; }
154 uint8_t coverageScale() const { return fCoverageScale; }
155
156 void getGLSLProcessorKey(const GrShaderCaps& caps, GrProcessorKeyBuilder* b) const override;
157
158 GrGLSLPrimitiveProcessor* createGLSLInstance(const GrShaderCaps&) const override;
159
160private:
161 friend class ::SkArenaAlloc; // for access to ctor
162
163 GrQuadEffect(const SkPMColor4f&, const SkMatrix& viewMatrix, uint8_t coverage,
164 const SkMatrix& localMatrix, bool usesLocalCoords);
165
166 SkPMColor4f fColor;
167 SkMatrix fViewMatrix;
168 SkMatrix fLocalMatrix;
169 bool fUsesLocalCoords;
170 uint8_t fCoverageScale;
171
172 static constexpr Attribute kAttributes[] = {
173 {"inPosition", kFloat2_GrVertexAttribType, kFloat2_GrSLType},
174 {"inHairQuadEdge", kFloat4_GrVertexAttribType, kHalf4_GrSLType}
175 };
176
177 GR_DECLARE_GEOMETRY_PROCESSOR_TEST
178
179 typedef GrGeometryProcessor INHERITED;
180};
181
182#endif
183