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/*
* 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 "GrCCPRTriangleShader.h"
#include "glsl/GrGLSLFragmentShaderBuilder.h"
#include "glsl/GrGLSLVertexGeoBuilder.h"
using Shader = GrCCPRCoverageProcessor::Shader;
Shader::WindHandling GrCCPRTriangleShader::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 GrCCPRTriangleShader::onEmitFragmentCode(GrGLSLPPFragmentBuilder* f,
const char* outputCoverage) const {
f->codeAppendf("%s = %s;", outputCoverage, fCoverageTimesWind.fsIn());
}
void GrCCPRTriangleCornerShader::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
GrCCPRTriangleCornerShader::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 GrCCPRTriangleCornerShader::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);
}
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