Refactor CCPR coverage shaders for a vertex impl

Decouples geometry generation and analytic coverage. This paves the
way for a vertex shader implementation.

Bug: skia:
Change-Id: I23b79d4397db22bd8fc063b8dfca58ab00037292
Reviewed-on: https://skia-review.googlesource.com/59200
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>

1 files changed, 278 insertions, 0 deletions

diff --git a/src/gpu/ccpr/GrCCPRCoverageProcessor_GSImpl.cpp b/src/gpu/ccpr/GrCCPRCoverageProcessor_GSImpl.cpp
new file mode 100644
index 0000000000..b9a38e732a
--- /dev/null
+++ b/src/gpu/ccpr/GrCCPRCoverageProcessor_GSImpl.cpp
@@ -0,0 +1,278 @@
+/*
+ * 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 "GrCCPRCoverageProcessor.h"
+
+#include "glsl/GrGLSLGeometryShaderBuilder.h"
+#include "glsl/GrGLSLVertexShaderBuilder.h"
+
+using Shader = GrCCPRCoverageProcessor::Shader;
+
+/**
+ * This class and its subclasses implement the coverage processor with geometry shaders.
+ */
+class GrCCPRCoverageProcessor::GSImpl : public GrGLSLGeometryProcessor {
+protected:
+    GSImpl(std::unique_ptr<Shader> shader) : fShader(std::move(shader)) {}
+
+    void setData(const GrGLSLProgramDataManager& pdman, const GrPrimitiveProcessor&,
+                 FPCoordTransformIter&& transformIter) final {
+        this->setTransformDataHelper(SkMatrix::I(), pdman, &transformIter);
+    }
+
+    void onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) final {
+        const GrCCPRCoverageProcessor& proc = args.fGP.cast<GrCCPRCoverageProcessor>();
+
+        // Vertex shader.
+        GrGLSLVertexBuilder* v = args.fVertBuilder;
+        // The Intel GLSL compiler hits an internal assertion if we index the input attrib itself
+        // with sk_VertexID.
+        v->codeAppendf("int pointID = sk_VertexID;");
+        v->codeAppend ("float2 self = ");
+        fShader->appendInputPointFetch(proc, v, args.fTexelBuffers[0], "pointID");
+        v->codeAppend (".xy;");
+        v->codeAppendf("int packedoffset = %s[%i];",
+                       proc.fInstanceAttrib.fName, proc.atlasOffsetIdx());
+        v->codeAppend ("float2 atlasoffset = float2((packedoffset << 16) >> 16, "
+                                                   "packedoffset >> 16);");
+        v->codeAppend ("self += atlasoffset;");
+        gpArgs->fPositionVar.set(kFloat2_GrSLType, "self");
+
+        // Geometry shader.
+        GrGLSLVaryingHandler* varyingHandler = args.fVaryingHandler;
+        this->emitGeometryShader(proc, varyingHandler, args.fGeomBuilder, args.fRTAdjustName);
+        varyingHandler->emitAttributes(proc);
+        SkASSERT(!args.fFPCoordTransformHandler->nextCoordTransform());
+
+        // Fragment shader.
+        fShader->emitFragmentCode(proc, args.fFragBuilder, args.fOutputColor, args.fOutputCoverage);
+    }
+
+    void emitGeometryShader(const GrCCPRCoverageProcessor& proc,
+                            GrGLSLVaryingHandler* varyingHandler, GrGLSLGeometryBuilder* g,
+                            const char* rtAdjust) const {
+        using InputType = GrGLSLGeometryBuilder::InputType;
+        using OutputType = GrGLSLGeometryBuilder::OutputType;
+
+        int numPts = fShader->getNumInputPoints();
+        SkASSERT(3 == numPts || 4 == numPts);
+
+        g->codeAppendf("float%ix2 pts = float%ix2(", numPts, numPts);
+        for (int i = 0; i < numPts; ++i) {
+            g->codeAppend (i ? ", " : "");
+            g->codeAppendf("sk_in[%i].sk_Position.xy", i);
+        }
+        g->codeAppend (");");
+
+        GrShaderVar wind("wind", kHalf_GrSLType);
+        g->declareGlobal(wind);
+        fShader->emitWind(g, "pts", rtAdjust, wind.c_str());
+
+        SkString emitVertexFn;
+        SkSTArray<2, GrShaderVar> emitArgs;
+        const char* position = emitArgs.emplace_back("position", kFloat2_GrSLType).c_str();
+        const char* coverage = emitArgs.emplace_back("coverage", kHalf_GrSLType).c_str();
+        g->emitFunction(kVoid_GrSLType, "emitVertex", emitArgs.count(), emitArgs.begin(), [&]() {
+            SkString fnBody;
+            fShader->emitVaryings(varyingHandler, &fnBody, position, coverage, wind.c_str());
+            fnBody.append("sk_Position = float4(position, 0, 1);");
+            fnBody.append("EmitVertex();");
+            return fnBody;
+        }().c_str(), &emitVertexFn);
+
+        g->codeAppendf("float2 bloat = %f * abs(%s.xz);", kAABloatRadius, rtAdjust);
+#ifdef SK_DEBUG
+        if (proc.debugVisualizationsEnabled()) {
+            g->codeAppendf("bloat *= %f;", proc.debugBloat());
+        }
+#endif
+
+        Shader::GeometryVars vars;
+        fShader->emitSetupCode(g, "pts", "sk_InvocationID", "bloat", wind.c_str(), rtAdjust, &vars);
+        int maxPoints = this->onEmitGeometryShader(g, wind, emitVertexFn.c_str(), rtAdjust, vars);
+
+        int numInputPoints = fShader->getNumInputPoints();
+        SkASSERT(3 == numInputPoints || 4 == numInputPoints);
+        InputType inputType = (3 == numInputPoints) ? InputType::kTriangles
+                                                    : InputType::kLinesAdjacency;
+
+        g->configure(inputType, OutputType::kTriangleStrip, maxPoints, fShader->getNumSegments());
+    }
+
+    virtual int onEmitGeometryShader(GrGLSLGeometryBuilder*, const GrShaderVar& wind,
+                                     const char* emitVertexFn, const char* rtAdjust,
+                                     const Shader::GeometryVars&) const = 0;
+
+    virtual ~GSImpl() {}
+
+    const std::unique_ptr<Shader> fShader;
+
+    typedef GrGLSLGeometryProcessor INHERITED;
+};
+
+class GSHullImpl : public GrCCPRCoverageProcessor::GSImpl {
+public:
+    GSHullImpl(std::unique_ptr<Shader> shader) : GSImpl(std::move(shader)) {}
+
+    int onEmitGeometryShader(GrGLSLGeometryBuilder* g, const GrShaderVar& wind,
+                             const char* emitVertexFn, const char* rtAdjust,
+                             const Shader::GeometryVars& vars) const override {
+        int numSides = fShader->getNumSegments();
+        SkASSERT(numSides >= 3);
+
+        const char* hullPts = vars.fHullVars.fAlternatePoints;
+        if (!hullPts) {
+            SkASSERT(fShader->getNumInputPoints() == numSides);
+            hullPts = "pts";
+        }
+
+        const char* midpoint = vars.fHullVars.fAlternateMidpoint;
+        if (!midpoint) {
+            g->codeAppendf("float2 midpoint = %s * float%i(%f);", hullPts, numSides, 1.0/numSides);
+            midpoint = "midpoint";
+        }
+
+        g->codeAppendf("int previdx = (sk_InvocationID + %i) %% %i, "
+                           "nextidx = (sk_InvocationID + 1) %% %i;",
+                       numSides - 1, numSides, numSides);
+
+        g->codeAppendf("float2 self = %s[sk_InvocationID];"
+                       "int leftidx = %s > 0 ? previdx : nextidx;"
+                       "int rightidx = %s > 0 ? nextidx : previdx;",
+                       hullPts, wind.c_str(), wind.c_str());
+
+        // Which quadrant does the vector from self -> right fall into?
+        g->codeAppendf("float2 right = %s[rightidx];", hullPts);
+        if (3 == numSides) {
+            // TODO: evaluate perf gains.
+            g->codeAppend ("float2 qsr = sign(right - self);");
+        } else {
+            SkASSERT(4 == numSides);
+            g->codeAppendf("float2 diag = %s[(sk_InvocationID + 2) %% 4];", hullPts);
+            g->codeAppend ("float2 qsr = sign((right != self ? right : diag) - self);");
+        }
+
+        // Which quadrant does the vector from left -> self fall into?
+        g->codeAppendf("float2 qls = sign(self - %s[leftidx]);", hullPts);
+
+        // d2 just helps us reduce triangle counts with orthogonal, axis-aligned lines.
+        // TODO: evaluate perf gains.
+        const char* dr2 = "dr";
+        if (3 == numSides) {
+            // TODO: evaluate perf gains.
+            g->codeAppend ("float2 dr = float2(qsr.y != 0 ? +qsr.y : +qsr.x, "
+                                              "qsr.x != 0 ? -qsr.x : +qsr.y);");
+            g->codeAppend ("float2 dr2 = float2(qsr.y != 0 ? +qsr.y : -qsr.x, "
+                                               "qsr.x != 0 ? -qsr.x : -qsr.y);");
+            g->codeAppend ("float2 dl = float2(qls.y != 0 ? +qls.y : +qls.x, "
+                                              "qls.x != 0 ? -qls.x : +qls.y);");
+            dr2 = "dr2";
+        } else {
+            g->codeAppend ("float2 dr = float2(qsr.y != 0 ? +qsr.y : 1, "
+                                              "qsr.x != 0 ? -qsr.x : 1);");
+            g->codeAppend ("float2 dl = (qls == float2(0)) ? dr : "
+                                       "float2(qls.y != 0 ? +qls.y : 1, qls.x != 0 ? -qls.x : 1);");
+        }
+        g->codeAppendf("bool2 dnotequal = notEqual(%s, dl);", dr2);
+
+        // Emit one third of what is the convex hull of pixel-size boxes centered on the vertices.
+        // Each invocation emits a different third.
+        g->codeAppendf("%s(right + bloat * dr, 1);", emitVertexFn);
+        g->codeAppendf("%s(%s, 1);", emitVertexFn, midpoint);
+        g->codeAppendf("%s(self + bloat * %s, 1);", emitVertexFn, dr2);
+        g->codeAppend ("if (any(dnotequal)) {");
+        g->codeAppendf(    "%s(self + bloat * dl, 1);", emitVertexFn);
+        g->codeAppend ("}");
+        g->codeAppend ("if (all(dnotequal)) {");
+        g->codeAppendf(    "%s(self + bloat * float2(-dl.y, dl.x), 1);", emitVertexFn);
+        g->codeAppend ("}");
+        g->codeAppend ("EndPrimitive();");
+
+        return 5;
+    }
+};
+
+class GSEdgeImpl : public GrCCPRCoverageProcessor::GSImpl {
+public:
+    GSEdgeImpl(std::unique_ptr<Shader> shader) : GSImpl(std::move(shader)) {}
+
+    int onEmitGeometryShader(GrGLSLGeometryBuilder* g, const GrShaderVar& wind,
+                             const char* emitVertexFn, const char* rtAdjust,
+                             const Shader::GeometryVars&) const override {
+        int numSides = fShader->getNumSegments();
+
+        g->codeAppendf("int nextidx = (sk_InvocationID + 1) %% %i;", numSides);
+        g->codeAppendf("float2 left = pts[%s > 0 ? sk_InvocationID : nextidx], "
+                                     "right = pts[%s > 0 ? nextidx : sk_InvocationID];",
+                                     wind.c_str(), wind.c_str());
+
+        Shader::EmitEdgeDistanceEquation(g, "left", "right", "float3 edge_distance_equation");
+
+        // qlr is defined in EmitEdgeDistanceEquation. TODO: address in a followup CL!
+        g->codeAppend ("float2x2 outer_pts = float2x2(left - bloat * qlr, right + bloat * qlr);");
+        g->codeAppend ("half2 outer_coverage = edge_distance_equation.xy * outer_pts + "
+                                              "edge_distance_equation.z;");
+
+        // d1 is defined in EmitEdgeDistanceEquation. TODO: address in a followup CL!
+        g->codeAppend ("float2 d2 = d1;");
+        g->codeAppend ("bool aligned = qlr.x == 0 || qlr.y == 0;");
+        g->codeAppend ("if (aligned) {");
+        g->codeAppend (    "d1 -= qlr;");
+        g->codeAppend (    "d2 += qlr;");
+        g->codeAppend ("}");
+
+        // Emit the convex hull of 2 pixel-size boxes centered on the endpoints of the edge. Each
+        // invocation emits a different edge. Emit negative coverage that subtracts the appropiate
+        // amount back out from the hull we drew above.
+        g->codeAppend ("if (!aligned) {");
+        g->codeAppendf(    "%s(outer_pts[0], outer_coverage[0]);", emitVertexFn);
+        g->codeAppend ("}");
+        g->codeAppendf("%s(left + bloat * d1, -1);", emitVertexFn);
+        g->codeAppendf("%s(left - bloat * d2, 0);", emitVertexFn);
+        g->codeAppendf("%s(right + bloat * d2, -1);", emitVertexFn);
+        g->codeAppendf("%s(right - bloat * d1, 0);", emitVertexFn);
+        g->codeAppend ("if (!aligned) {");
+        g->codeAppendf(    "%s(outer_pts[1], outer_coverage[1]);", emitVertexFn);
+        g->codeAppend ("}");
+        g->codeAppend ("EndPrimitive();");
+
+        return 6;
+    }
+};
+
+class GSCornerImpl : public GrCCPRCoverageProcessor::GSImpl {
+public:
+    GSCornerImpl(std::unique_ptr<Shader> shader) : GSImpl(std::move(shader)) {}
+
+    int onEmitGeometryShader(GrGLSLGeometryBuilder* g, const GrShaderVar& wind,
+                             const char* emitVertexFn, const char* rtAdjust,
+                             const Shader::GeometryVars& vars) const override {
+        const char* corner = vars.fCornerVars.fPoint;
+        SkASSERT(corner);
+
+        g->codeAppendf("%s(%s + float2(-bloat.x, -bloat.y), 1);", emitVertexFn, corner);
+        g->codeAppendf("%s(%s + float2(-bloat.x, +bloat.y), 1);", emitVertexFn, corner);
+        g->codeAppendf("%s(%s + float2(+bloat.x, -bloat.y), 1);", emitVertexFn, corner);
+        g->codeAppendf("%s(%s + float2(+bloat.x, +bloat.y), 1);", emitVertexFn, corner);
+        g->codeAppend ("EndPrimitive();");
+
+        return 4;
+    }
+};
+
+GrGLSLPrimitiveProcessor* GrCCPRCoverageProcessor::CreateGSImpl(std::unique_ptr<Shader> shader) {
+    switch (shader->getGeometryType()) {
+        case Shader::GeometryType::kHull:
+            return new GSHullImpl(std::move(shader));
+        case Shader::GeometryType::kEdges:
+            return new GSEdgeImpl(std::move(shader));
+        case Shader::GeometryType::kCorners:
+            return new GSCornerImpl(std::move(shader));
+    }
+    SK_ABORT("Unexpected Shader::GeometryType.");
+    return nullptr;
+}