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1 /*
2  * Copyright 2018 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 #include "GrCCConicShader.h"
9 
10 #include "glsl/GrGLSLFragmentShaderBuilder.h"
11 #include "glsl/GrGLSLVertexGeoBuilder.h"
12 
emitSetupCode(GrGLSLVertexGeoBuilder * s,const char * pts,const char * wind,const char ** outHull4) const13 void GrCCConicShader::emitSetupCode(GrGLSLVertexGeoBuilder* s, const char* pts, const char* wind,
14                                     const char** outHull4) const {
15     // K is distance from the line P2 -> P0. L is distance from the line P0 -> P1, scaled by 2w.
16     // M is distance from the line P1 -> P2, scaled by 2w. We do this in a space where P1=0.
17     s->declareGlobal(fKLMMatrix);
18     s->codeAppendf("float x0 = %s[0].x - %s[1].x, x2 = %s[2].x - %s[1].x;", pts, pts, pts, pts);
19     s->codeAppendf("float y0 = %s[0].y - %s[1].y, y2 = %s[2].y - %s[1].y;", pts, pts, pts, pts);
20     s->codeAppendf("float w = %s[3].x;", pts);
21     s->codeAppendf("%s = float3x3(y2 - y0, x0 - x2, x2*y0 - x0*y2, "
22                                  "2*w * float2(+y0, -x0), 0, "
23                                  "2*w * float2(-y2, +x2), 0);", fKLMMatrix.c_str());
24 
25     s->declareGlobal(fControlPoint);
26     s->codeAppendf("%s = %s[1];", fControlPoint.c_str(), pts);
27 
28     // Scale KLM by the inverse Manhattan width of K. This allows K to double as the flat opposite
29     // edge AA. kwidth will not be 0 because we cull degenerate conics on the CPU.
30     s->codeAppendf("float kwidth = 2*bloat * %s * (abs(%s[0].x) + abs(%s[0].y));",
31                    wind, fKLMMatrix.c_str(), fKLMMatrix.c_str());
32     s->codeAppendf("%s *= 1/kwidth;", fKLMMatrix.c_str());
33 
34     if (outHull4) {
35         // Clip the conic triangle by the tangent line at maximum height. Conics have the nice
36         // property that maximum height always occurs at T=.5. This is a simple application for
37         // De Casteljau's algorithm.
38         s->codeAppendf("float2 p1w = %s[1]*w;", pts);
39         s->codeAppend ("float r = 1 / (1 + w);");
40         s->codeAppend ("float2 conic_hull[4];");
41         s->codeAppendf("conic_hull[0] = %s[0];", pts);
42         s->codeAppendf("conic_hull[1] = (%s[0] + p1w) * r;", pts);
43         s->codeAppendf("conic_hull[2] = (p1w + %s[2]) * r;", pts);
44         s->codeAppendf("conic_hull[3] = %s[2];", pts);
45         *outHull4 = "conic_hull";
46     }
47 }
48 
onEmitVaryings(GrGLSLVaryingHandler * varyingHandler,GrGLSLVarying::Scope scope,SkString * code,const char * position,const char * coverage,const char * cornerCoverage)49 void GrCCConicShader::onEmitVaryings(GrGLSLVaryingHandler* varyingHandler,
50                                      GrGLSLVarying::Scope scope, SkString* code,
51                                      const char* position, const char* coverage,
52                                      const char* cornerCoverage) {
53     fKLM_fWind.reset(kFloat4_GrSLType, scope);
54     varyingHandler->addVarying("klm_and_wind", &fKLM_fWind);
55     code->appendf("float3 klm = float3(%s - %s, 1) * %s;",
56                   position, fControlPoint.c_str(), fKLMMatrix.c_str());
57     code->appendf("%s.xyz = klm;", OutName(fKLM_fWind));
58     code->appendf("%s.w = %s;", OutName(fKLM_fWind), coverage); // coverage == wind.
59 
60     fGrad_fCorner.reset(cornerCoverage ? kFloat4_GrSLType : kFloat2_GrSLType, scope);
61     varyingHandler->addVarying(cornerCoverage ? "grad_and_corner" : "grad", &fGrad_fCorner);
62     code->appendf("%s.xy = 2*bloat * (float3x2(%s) * float3(2*klm[0], -klm[2], -klm[1]));",
63                   OutName(fGrad_fCorner), fKLMMatrix.c_str());
64 
65     if (cornerCoverage) {
66         code->appendf("half hull_coverage;");
67         this->calcHullCoverage(code, "klm", OutName(fGrad_fCorner), "hull_coverage");
68         code->appendf("%s.zw = half2(hull_coverage, 1) * %s;",
69                       OutName(fGrad_fCorner), cornerCoverage);
70     }
71 }
72 
onEmitFragmentCode(GrGLSLFPFragmentBuilder * f,const char * outputCoverage) const73 void GrCCConicShader::onEmitFragmentCode(GrGLSLFPFragmentBuilder* f,
74                                          const char* outputCoverage) const {
75     this->calcHullCoverage(&AccessCodeString(f), fKLM_fWind.fsIn(), fGrad_fCorner.fsIn(),
76                            outputCoverage);
77     f->codeAppendf("%s *= %s.w;", outputCoverage, fKLM_fWind.fsIn()); // Wind.
78 
79     if (kFloat4_GrSLType == fGrad_fCorner.type()) {
80         f->codeAppendf("%s = %s.z * %s.w + %s;", // Attenuated corner coverage.
81                        outputCoverage, fGrad_fCorner.fsIn(), fGrad_fCorner.fsIn(),
82                        outputCoverage);
83     }
84 }
85 
calcHullCoverage(SkString * code,const char * klm,const char * grad,const char * outputCoverage) const86 void GrCCConicShader::calcHullCoverage(SkString* code, const char* klm, const char* grad,
87                                        const char* outputCoverage) const {
88     code->appendf("float k = %s.x, l = %s.y, m = %s.z;", klm, klm, klm);
89     code->append ("float f = k*k - l*m;");
90     code->appendf("float fwidth = abs(%s.x) + abs(%s.y);", grad, grad);
91     code->appendf("%s = min(0.5 - f/fwidth, 1);", outputCoverage); // Curve coverage.
92     code->append ("half d = min(k - 0.5, 0);"); // K doubles as the flat opposite edge's AA.
93     code->appendf("%s = max(%s + d, 0);", outputCoverage, outputCoverage); // Total hull coverage.
94 }
95