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/*
* Copyright 2013 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef GrBezierEffect_DEFINED
#define GrBezierEffect_DEFINED
#include "include/core/SkMatrix.h"
#include "include/private/SkColorData.h"
#include "include/private/gpu/ganesh/GrTypesPriv.h"
#include "src/base/SkArenaAlloc.h"
#include "src/core/SkSLTypeShared.h"
#include "src/gpu/ganesh/GrCaps.h"
#include "src/gpu/ganesh/GrGeometryProcessor.h"
#include "src/gpu/ganesh/GrProcessorUnitTest.h"
#include "src/gpu/ganesh/GrShaderCaps.h"
#include <cstdint>
#include <memory>
namespace skgpu { class KeyBuilder; }
/**
* Shader is based off of Loop-Blinn Quadratic GPU Rendering
* The output of this effect is a hairline edge for conics.
* Conics specified by implicit equation K^2 - LM.
* K, L, and M, are the first three values of the vertex attribute,
* the fourth value is not used. Distance is calculated using a
* first order approximation from the taylor series.
* Coverage for AA is max(0, 1-distance).
*
* Test were also run using a second order distance approximation.
* There were two versions of the second order approx. The first version
* is of roughly the form:
* f(q) = |f(p)| - ||f'(p)||*||q-p|| - ||f''(p)||*||q-p||^2.
* The second is similar:
* f(q) = |f(p)| + ||f'(p)||*||q-p|| + ||f''(p)||*||q-p||^2.
* The exact version of the equations can be found in the paper
* "Distance Approximations for Rasterizing Implicit Curves" by Gabriel Taubin
*
* In both versions we solve the quadratic for ||q-p||.
* Version 1:
* gFM is magnitude of first partials and gFM2 is magnitude of 2nd partials (as derived from paper)
* builder->fsCodeAppend("\t\tedgeAlpha = (sqrt(gFM*gFM+4.0*func*gF2M) - gFM)/(2.0*gF2M);\n");
* Version 2:
* builder->fsCodeAppend("\t\tedgeAlpha = (gFM - sqrt(gFM*gFM-4.0*func*gF2M))/(2.0*gF2M);\n");
*
* Also note that 2nd partials of k,l,m are zero
*
* When comparing the two second order approximations to the first order approximations,
* the following results were found. Version 1 tends to underestimate the distances, thus it
* basically increases all the error that we were already seeing in the first order
* approx. So this version is not the one to use. Version 2 has the opposite effect
* and tends to overestimate the distances. This is much closer to what we are
* looking for. It is able to render ellipses (even thin ones) without the need to chop.
* However, it can not handle thin hyperbolas well and thus would still rely on
* chopping to tighten the clipping. Another side effect of the overestimating is
* that the curves become much thinner and "ropey". If all that was ever rendered
* were "not too thin" curves and ellipses then 2nd order may have an advantage since
* only one geometry would need to be rendered. However no benches were run comparing
* chopped first order and non chopped 2nd order.
*/
class GrConicEffect : public GrGeometryProcessor {
public:
static GrGeometryProcessor* Make(SkArenaAlloc* arena,
const SkPMColor4f& color,
const SkMatrix& viewMatrix,
const GrCaps& caps,
const SkMatrix& localMatrix,
bool usesLocalCoords,
uint8_t coverage = 0xff) {
if (!caps.shaderCaps()->fShaderDerivativeSupport) {
return nullptr;
}
return arena->make([&](void* ptr) {
return new (ptr) GrConicEffect(color, viewMatrix, coverage, localMatrix,
usesLocalCoords);
});
}
~GrConicEffect() override;
const char* name() const override { return "Conic"; }
void addToKey(const GrShaderCaps& caps, skgpu::KeyBuilder* b) const override;
std::unique_ptr<ProgramImpl> makeProgramImpl(const GrShaderCaps&) const override;
private:
class Impl;
GrConicEffect(const SkPMColor4f&, const SkMatrix& viewMatrix, uint8_t coverage,
const SkMatrix& localMatrix, bool usesLocalCoords);
inline const Attribute& inPosition() const { return kAttributes[0]; }
inline const Attribute& inConicCoeffs() const { return kAttributes[1]; }
SkPMColor4f fColor;
SkMatrix fViewMatrix;
SkMatrix fLocalMatrix;
bool fUsesLocalCoords;
uint8_t fCoverageScale;
inline static constexpr Attribute kAttributes[] = {
{"inPosition", kFloat2_GrVertexAttribType, SkSLType::kFloat2},
{"inConicCoeffs", kFloat4_GrVertexAttribType, SkSLType::kHalf4}
};
GR_DECLARE_GEOMETRY_PROCESSOR_TEST
using INHERITED = GrGeometryProcessor;
};
///////////////////////////////////////////////////////////////////////////////
/**
* The output of this effect is a hairline edge for quadratics.
* Quadratic specified by 0=u^2-v canonical coords. u and v are the first
* two components of the vertex attribute. At the three control points that define
* the Quadratic, u, v have the values {0,0}, {1/2, 0}, and {1, 1} respectively.
* Coverage for AA is min(0, 1-distance). 3rd & 4th cimponent unused.
* Requires shader derivative instruction support.
*/
class GrQuadEffect : public GrGeometryProcessor {
public:
static GrGeometryProcessor* Make(SkArenaAlloc* arena,
const SkPMColor4f& color,
const SkMatrix& viewMatrix,
const GrCaps& caps,
const SkMatrix& localMatrix,
bool usesLocalCoords,
uint8_t coverage = 0xff) {
if (!caps.shaderCaps()->fShaderDerivativeSupport) {
return nullptr;
}
return arena->make([&](void* ptr) {
return new (ptr) GrQuadEffect(color, viewMatrix, coverage, localMatrix,
usesLocalCoords);
});
}
~GrQuadEffect() override;
const char* name() const override { return "Quad"; }
void addToKey(const GrShaderCaps& caps, skgpu::KeyBuilder* b) const override;
std::unique_ptr<ProgramImpl> makeProgramImpl(const GrShaderCaps&) const override;
private:
class Impl;
GrQuadEffect(const SkPMColor4f&, const SkMatrix& viewMatrix, uint8_t coverage,
const SkMatrix& localMatrix, bool usesLocalCoords);
inline const Attribute& inPosition() const { return kAttributes[0]; }
inline const Attribute& inHairQuadEdge() const { return kAttributes[1]; }
SkPMColor4f fColor;
SkMatrix fViewMatrix;
SkMatrix fLocalMatrix;
bool fUsesLocalCoords;
uint8_t fCoverageScale;
inline static constexpr Attribute kAttributes[] = {
{"inPosition", kFloat2_GrVertexAttribType, SkSLType::kFloat2},
{"inHairQuadEdge", kFloat4_GrVertexAttribType, SkSLType::kHalf4}
};
GR_DECLARE_GEOMETRY_PROCESSOR_TEST
using INHERITED = GrGeometryProcessor;
};
#endif