/* * 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 { … }; /////////////////////////////////////////////////////////////////////////////// /** * 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 { … }; #endif
Codebase Browser
chromium