1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
|
/*
* Copyright 2017 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "GrCCTriangleShader.h"
#include "glsl/GrGLSLFragmentShaderBuilder.h"
#include "glsl/GrGLSLVertexGeoBuilder.h"
using Shader = GrCCCoverageProcessor::Shader;
Shader::WindHandling GrCCTriangleShader::onEmitVaryings(GrGLSLVaryingHandler* varyingHandler,
GrGLSLVarying::Scope scope,
SkString* code, const char* /*position*/,
const char* coverage, const char* wind) {
fCoverageTimesWind.reset(kHalf_GrSLType, scope);
if (!coverage) {
varyingHandler->addFlatVarying("wind", &fCoverageTimesWind);
code->appendf("%s = %s;", OutName(fCoverageTimesWind), wind);
} else {
varyingHandler->addVarying("coverage_times_wind", &fCoverageTimesWind);
code->appendf("%s = %s * %s;", OutName(fCoverageTimesWind), coverage, wind);
}
return WindHandling::kHandled;
}
void GrCCTriangleShader::onEmitFragmentCode(GrGLSLPPFragmentBuilder* f,
const char* outputCoverage) const {
f->codeAppendf("%s = %s;", outputCoverage, fCoverageTimesWind.fsIn());
}
void GrCCTriangleCornerShader::emitSetupCode(GrGLSLVertexGeoBuilder* s, const char* pts,
const char* repetitionID, const char* wind,
GeometryVars* vars) const {
s->codeAppendf("float2 corner = %s[%s];", pts, repetitionID);
vars->fCornerVars.fPoint = "corner";
s->codeAppendf("float2x2 vectors = float2x2(corner - %s[0 != %s ? %s - 1 : 2], "
"corner - %s[2 != %s ? %s + 1 : 0]);",
pts, repetitionID, repetitionID, pts, repetitionID,
repetitionID);
// Make sure neither vector is 0 to avoid a divide-by-zero. Wind will be zero anyway if this
// is the case, so whatever we output won't have any effect as long it isn't NaN or Inf.
s->codeAppend ("for (int i = 0; i < 2; ++i) {");
s->codeAppend ( "vectors[i] = (vectors[i] != float2(0)) ? vectors[i] : float2(1);");
s->codeAppend ("}");
// Find the vector that bisects the region outside the incoming edges. Each edge is
// responsible to subtract the outside region on its own the side of the bisector.
s->codeAppendf("float2 leftdir = normalize(vectors[%s > 0 ? 0 : 1]);", wind);
s->codeAppendf("float2 rightdir = normalize(vectors[%s > 0 ? 1 : 0]);", wind);
s->codeAppend ("float2 bisect = dot(leftdir, rightdir) >= 0 ? "
"leftdir + rightdir : "
"float2(leftdir.y - rightdir.y, rightdir.x - leftdir.x);");
// In ccpr we don't calculate exact geometric pixel coverage. What the distance-to-edge
// method actually finds is coverage inside a logical "AA box", one that is rotated inline
// with the edge, and in our case, up-scaled to circumscribe the actual pixel. Below we set
// up transformations into normalized logical AA box space for both incoming edges. These
// will tell the fragment shader where the corner is located within each edge's AA box.
s->declareGlobal(fAABoxMatrices);
s->declareGlobal(fAABoxTranslates);
s->declareGlobal(fGeoShaderBisects);
s->codeAppendf("for (int i = 0; i < 2; ++i) {");
// The X component runs parallel to the edge (i.e. distance to the corner).
s->codeAppendf( "float2 n = -vectors[%s > 0 ? i : 1 - i];", wind);
s->codeAppend ( "float nwidth = (abs(n.x) + abs(n.y)) * (bloat * 2);");
s->codeAppend ( "n /= nwidth;"); // nwidth != 0 because both vectors != 0.
s->codeAppendf( "%s[i][0] = n;", fAABoxMatrices.c_str());
s->codeAppendf( "%s[i][0] = -dot(n, corner) + .5;", fAABoxTranslates.c_str());
// The Y component runs perpendicular to the edge (i.e. distance-to-edge).
s->codeAppend ( "n = (i == 0) ? float2(-n.y, n.x) : float2(n.y, -n.x);");
s->codeAppendf( "%s[i][1] = n;", fAABoxMatrices.c_str());
s->codeAppendf( "%s[i][1] = -dot(n, corner) + .5;", fAABoxTranslates.c_str());
// Translate the bisector into logical AA box space.
// NOTE: Since the region outside two edges of a convex shape is in [180 deg, 360 deg], the
// bisector will therefore be in [90 deg, 180 deg]. Or, x >= 0 and y <= 0 in AA box space.
s->codeAppendf( "%s[i] = -bisect * %s[i];",
fGeoShaderBisects.c_str(), fAABoxMatrices.c_str());
s->codeAppend ("}");
}
Shader::WindHandling
GrCCTriangleCornerShader::onEmitVaryings(GrGLSLVaryingHandler* varyingHandler,
GrGLSLVarying::Scope scope, SkString* code,
const char* position, const char* coverage,
const char* /*wind*/) {
SkASSERT(!coverage);
fCornerLocationInAABoxes.reset(kFloat2x2_GrSLType, scope);
varyingHandler->addVarying("corner_location_in_aa_boxes", &fCornerLocationInAABoxes);
fBisectInAABoxes.reset(kFloat2x2_GrSLType, scope);
varyingHandler->addFlatVarying("bisect_in_aa_boxes", &fBisectInAABoxes);
code->appendf("for (int i = 0; i < 2; ++i) {");
code->appendf( "%s[i] = %s * %s[i] + %s[i];",
OutName(fCornerLocationInAABoxes), position, fAABoxMatrices.c_str(),
fAABoxTranslates.c_str());
code->appendf( "%s[i] = %s[i];", OutName(fBisectInAABoxes), fGeoShaderBisects.c_str());
code->appendf("}");
return WindHandling::kNotHandled;
}
void GrCCTriangleCornerShader::onEmitFragmentCode(GrGLSLPPFragmentBuilder* f,
const char* outputCoverage) const {
// By the time we reach this shader, the pixel is in the following state:
//
// 1. The hull shader has emitted a coverage of 1.
// 2. Both edges have subtracted the area on their outside.
//
// This generally works, but it is a problem for corner pixels. There is a region within
// corner pixels that is outside both edges at the same time. This means the region has been
// double subtracted (once by each edge). The purpose of this shader is to fix these corner
// pixels.
//
// More specifically, each edge redoes its coverage analysis so that it only subtracts the
// outside area that falls on its own side of the bisector line.
//
// NOTE: unless the edges fall on multiples of 90 deg from one another, they will have
// different AA boxes. (For an explanation of AA boxes, see comments in
// onEmitGeometryShader.) This means the coverage analysis will only be approximate. It
// seems acceptable, but if we want exact coverage we will need to switch to a more
// expensive model.
f->codeAppendf("for (int i = 0; i < 2; ++i) {"); // Loop through both edges.
f->codeAppendf( "half2 corner = %s[i];", fCornerLocationInAABoxes.fsIn());
f->codeAppendf( "half2 bisect = %s[i];", fBisectInAABoxes.fsIn());
// Find the point at which the bisector exits the logical AA box.
// (The inequality works because bisect.x is known >= 0 and bisect.y is known <= 0.)
f->codeAppendf( "half2 d = half2(1 - corner.x, -corner.y);");
f->codeAppendf( "half T = d.y * bisect.x >= d.x * bisect.y ? d.y / bisect.y "
": d.x / bisect.x;");
f->codeAppendf( "half2 exit = corner + bisect * T;");
// These lines combined (and the final multiply by .5) accomplish the following:
// 1. Add back the area beyond the corner that was subtracted out previously.
// 2. Subtract out the area beyond the corner, but under the bisector.
// The other edge will take care of the area on its own side of the bisector.
f->codeAppendf( "%s += (2 - corner.x - exit.x) * corner.y;", outputCoverage);
f->codeAppendf( "%s += (corner.x - 1) * exit.y;", outputCoverage);
f->codeAppendf("}");
f->codeAppendf("%s *= .5;", outputCoverage);
}
|
