src/gpu/ccpr/GrCCPathProcessor.cpp - platform/external/skia - Gitiles

 /*
  * 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 "GrCCPathProcessor.h"

 #include "GrGpuCommandBuffer.h"
 #include "GrOnFlushResourceProvider.h"
 #include "GrTexture.h"
 #include "ccpr/GrCCPerFlushResources.h"
 #include "glsl/GrGLSLFragmentShaderBuilder.h"
 #include "glsl/GrGLSLGeometryProcessor.h"
 #include "glsl/GrGLSLProgramBuilder.h"
 #include "glsl/GrGLSLVarying.h"

 // Slightly undershoot an AA bloat radius of 0.5 so vertices that fall on integer boundaries don't
 // accidentally reach into neighboring path masks within the atlas.
 constexpr float kAABloatRadius = 0.491111f;

 // Paths are drawn as octagons. Each point on the octagon is the intersection of two lines: one edge
 // from the path's bounding box and one edge from its 45-degree bounding box. The below inputs
 // define a vertex by the two edges that need to be intersected. Normals point out of the octagon,
 // and the bounding boxes are sent in as instance attribs.
 static constexpr float kOctoEdgeNorms[8 * 4] = {
     // bbox   // bbox45
     -1, 0,    -1,+1,
     -1, 0,    -1,-1,
      0,-1,    -1,-1,
      0,-1,    +1,-1,
     +1, 0,    +1,-1,
     +1, 0,    +1,+1,
      0,+1,    +1,+1,
      0,+1,    -1,+1,
 };

 GR_DECLARE_STATIC_UNIQUE_KEY(gVertexBufferKey);

 sk_sp<const GrBuffer> GrCCPathProcessor::FindVertexBuffer(GrOnFlushResourceProvider* onFlushRP) {
     GR_DEFINE_STATIC_UNIQUE_KEY(gVertexBufferKey);
     return onFlushRP->findOrMakeStaticBuffer(kVertex_GrBufferType, sizeof(kOctoEdgeNorms),
                                              kOctoEdgeNorms, gVertexBufferKey);
 }

 static constexpr uint16_t kRestartStrip = 0xffff;

 static constexpr uint16_t kOctoIndicesAsStrips[] = {
     1, 0, 2, 4, 3, kRestartStrip, // First half.
     5, 4, 6, 0, 7 // Second half.
 };

 static constexpr uint16_t kOctoIndicesAsTris[] = {
     // First half.
     1, 0, 2,
     0, 4, 2,
     2, 4, 3,

     // Second half.
     5, 4, 6,
     4, 0, 6,
     6, 0, 7,
 };

 GR_DECLARE_STATIC_UNIQUE_KEY(gIndexBufferKey);

 constexpr GrPrimitiveProcessor::Attribute GrCCPathProcessor::kInstanceAttribs[];
 constexpr GrPrimitiveProcessor::Attribute GrCCPathProcessor::kEdgeNormsAttrib;

 sk_sp<const GrBuffer> GrCCPathProcessor::FindIndexBuffer(GrOnFlushResourceProvider* onFlushRP) {
     GR_DEFINE_STATIC_UNIQUE_KEY(gIndexBufferKey);
     if (onFlushRP->caps()->usePrimitiveRestart()) {
         return onFlushRP->findOrMakeStaticBuffer(kIndex_GrBufferType, sizeof(kOctoIndicesAsStrips),
                                                  kOctoIndicesAsStrips, gIndexBufferKey);
     } else {
         return onFlushRP->findOrMakeStaticBuffer(kIndex_GrBufferType, sizeof(kOctoIndicesAsTris),
                                                  kOctoIndicesAsTris, gIndexBufferKey);
     }
 }

 GrCCPathProcessor::GrCCPathProcessor(GrResourceProvider* resourceProvider,
                                      sk_sp<GrTextureProxy> atlas,
                                      const SkMatrix& viewMatrixIfUsingLocalCoords)
         : INHERITED(kGrCCPathProcessor_ClassID)
         , fAtlasAccess(std::move(atlas), GrSamplerState::Filter::kNearest,
                        GrSamplerState::WrapMode::kClamp, kFragment_GrShaderFlag) {
     this->setInstanceAttributeCnt(kNumInstanceAttribs);
     // Check that instance attributes exactly match Instance struct layout.
     SkASSERT(!strcmp(this->instanceAttribute(0).name(), "devbounds"));
     SkASSERT(!strcmp(this->instanceAttribute(1).name(), "devbounds45"));
     SkASSERT(!strcmp(this->instanceAttribute(2).name(), "dev_to_atlas_offset"));
     SkASSERT(!strcmp(this->instanceAttribute(3).name(), "color"));
     SkASSERT(this->debugOnly_instanceAttributeOffset(0) == offsetof(Instance, fDevBounds));
     SkASSERT(this->debugOnly_instanceAttributeOffset(1) == offsetof(Instance, fDevBounds45));
     SkASSERT(this->debugOnly_instanceAttributeOffset(2) == offsetof(Instance, fDevToAtlasOffset));
     SkASSERT(this->debugOnly_instanceAttributeOffset(3) == offsetof(Instance, fColor));
     SkASSERT(this->debugOnly_instanceStride() == sizeof(Instance));

     this->setVertexAttributeCnt(1);

     fAtlasAccess.instantiate(resourceProvider);
     this->addTextureSampler(&fAtlasAccess);

     if (!viewMatrixIfUsingLocalCoords.invert(&fLocalMatrix)) {
         fLocalMatrix.setIdentity();
     }
 }

 class GLSLPathProcessor : public GrGLSLGeometryProcessor {
 public:
     void onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) override;

 private:
     void setData(const GrGLSLProgramDataManager& pdman, const GrPrimitiveProcessor& primProc,
                  FPCoordTransformIter&& transformIter) override {
         const GrCCPathProcessor& proc = primProc.cast<GrCCPathProcessor>();
         pdman.set2f(fAtlasAdjustUniform, 1.0f / proc.atlas()->width(),
                     1.0f / proc.atlas()->height());
         this->setTransformDataHelper(proc.localMatrix(), pdman, &transformIter);
     }

     GrGLSLUniformHandler::UniformHandle fAtlasAdjustUniform;

     typedef GrGLSLGeometryProcessor INHERITED;
 };

 GrGLSLPrimitiveProcessor* GrCCPathProcessor::createGLSLInstance(const GrShaderCaps&) const {
     return new GLSLPathProcessor();
 }

 void GrCCPathProcessor::drawPaths(GrOpFlushState* flushState, const GrPipeline& pipeline,
                                   const GrCCPerFlushResources& resources, int baseInstance,
                                   int endInstance, const SkRect& bounds) const {
     const GrCaps& caps = flushState->caps();
     GrPrimitiveType primitiveType = caps.usePrimitiveRestart()
                                             ? GrPrimitiveType::kTriangleStrip
                                             : GrPrimitiveType::kTriangles;
     int numIndicesPerInstance = caps.usePrimitiveRestart()
                                         ? SK_ARRAY_COUNT(kOctoIndicesAsStrips)
                                         : SK_ARRAY_COUNT(kOctoIndicesAsTris);
     GrMesh mesh(primitiveType);
     auto enablePrimitiveRestart = GrPrimitiveRestart(flushState->caps().usePrimitiveRestart());

     mesh.setIndexedInstanced(resources.indexBuffer(), numIndicesPerInstance,
                              resources.instanceBuffer(), endInstance - baseInstance, baseInstance,
                              enablePrimitiveRestart);
     mesh.setVertexData(resources.vertexBuffer());

     flushState->rtCommandBuffer()->draw(*this, pipeline, &mesh, nullptr, 1, bounds);
 }

 void GLSLPathProcessor::onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) {
     using InstanceAttribs = GrCCPathProcessor::InstanceAttribs;
     using Interpolation = GrGLSLVaryingHandler::Interpolation;

     const GrCCPathProcessor& proc = args.fGP.cast<GrCCPathProcessor>();
     GrGLSLUniformHandler* uniHandler = args.fUniformHandler;
     GrGLSLVaryingHandler* varyingHandler = args.fVaryingHandler;

     const char* atlasAdjust;
     fAtlasAdjustUniform = uniHandler->addUniform(
             kVertex_GrShaderFlag,
             kFloat2_GrSLType, "atlas_adjust", &atlasAdjust);

     varyingHandler->emitAttributes(proc);

     GrGLSLVarying texcoord(kFloat3_GrSLType);
     GrGLSLVarying color(kHalf4_GrSLType);
     varyingHandler->addVarying("texcoord", &texcoord);
     varyingHandler->addPassThroughAttribute(proc.getInstanceAttrib(InstanceAttribs::kColor),
                                             args.fOutputColor, Interpolation::kCanBeFlat);

     // The vertex shader bloats and intersects the devBounds and devBounds45 rectangles, in order to
     // find an octagon that circumscribes the (bloated) path.
     GrGLSLVertexBuilder* v = args.fVertBuilder;

     // Each vertex is the intersection of one edge from devBounds and one from devBounds45.
     // 'N' holds the normals to these edges as column vectors.
     //
     // NOTE: "float2x2(float4)" is valid and equivalent to "float2x2(float4.xy, float4.zw)",
     // however Intel compilers crash when we use the former syntax in this shader.
     v->codeAppendf("float2x2 N = float2x2(%s.xy, %s.zw);", proc.getEdgeNormsAttrib().name(),
                    proc.getEdgeNormsAttrib().name());

     // N[0] is the normal for the edge we are intersecting from the regular bounding box, pointing
     // out of the octagon.
     v->codeAppendf("float4 devbounds = %s;",
                    proc.getInstanceAttrib(InstanceAttribs::kDevBounds).name());
     v->codeAppend ("float2 refpt = (0 == sk_VertexID >> 2)"
                            "? float2(min(devbounds.x, devbounds.z), devbounds.y)"
                            ": float2(max(devbounds.x, devbounds.z), devbounds.w);");
     v->codeAppendf("refpt += N[0] * %f;", kAABloatRadius); // bloat for AA.

     // N[1] is the normal for the edge we are intersecting from the 45-degree bounding box, pointing
     // out of the octagon.
     v->codeAppendf("float2 refpt45 = (0 == ((sk_VertexID + 1) & (1 << 2))) ? %s.xy : %s.zw;",
                    proc.getInstanceAttrib(InstanceAttribs::kDevBounds45).name(),
                    proc.getInstanceAttrib(InstanceAttribs::kDevBounds45).name());
     v->codeAppendf("refpt45 *= float2x2(.5,.5,-.5,.5);"); // transform back to device space.
     v->codeAppendf("refpt45 += N[1] * %f;", kAABloatRadius); // bloat for AA.

     v->codeAppend ("float2 K = float2(dot(N[0], refpt), dot(N[1], refpt45));");
     v->codeAppendf("float2 octocoord = K * inverse(N);");

     gpArgs->fPositionVar.set(kFloat2_GrSLType, "octocoord");

     // Convert to atlas coordinates in order to do our texture lookup.
     v->codeAppendf("float2 atlascoord = octocoord + float2(%s);",
                    proc.getInstanceAttrib(InstanceAttribs::kDevToAtlasOffset).name());
     if (kTopLeft_GrSurfaceOrigin == proc.atlasProxy()->origin()) {
         v->codeAppendf("%s.xy = atlascoord * %s;", texcoord.vsOut(), atlasAdjust);
     } else {
         SkASSERT(kBottomLeft_GrSurfaceOrigin == proc.atlasProxy()->origin());
         v->codeAppendf("%s.xy = float2(atlascoord.x * %s.x, 1 - atlascoord.y * %s.y);",
                        texcoord.vsOut(), atlasAdjust, atlasAdjust);
     }
     // The third texture coordinate is -.5 for even-odd paths and +.5 for winding ones.
     // ("right < left" indicates even-odd fill type.)
     v->codeAppendf("%s.z = sign(devbounds.z - devbounds.x) * .5;", texcoord.vsOut());

     this->emitTransforms(v, varyingHandler, uniHandler, GrShaderVar("octocoord", kFloat2_GrSLType),
                          proc.localMatrix(), args.fFPCoordTransformHandler);

     // Fragment shader.
     GrGLSLFPFragmentBuilder* f = args.fFragBuilder;

     // Look up coverage count in the atlas.
     f->codeAppend ("half coverage = ");
     f->appendTextureLookup(args.fTexSamplers[0], SkStringPrintf("%s.xy", texcoord.fsIn()).c_str(),
                            kFloat2_GrSLType);
     f->codeAppend (".a;");

     // Scale coverage count by .5. Make it negative for even-odd paths and positive for winding
     // ones. Clamp winding coverage counts at 1.0 (i.e. min(coverage/2, .5)).
     f->codeAppendf("coverage = min(abs(coverage) * %s.z, .5);", texcoord.fsIn());

     // For negative values, this finishes the even-odd sawtooth function. Since positive (winding)
     // values were clamped at "coverage/2 = .5", this only undoes the previous multiply by .5.
     f->codeAppend ("coverage = 1 - abs(fract(coverage) * 2 - 1);");

     f->codeAppendf("%s = half4(coverage);", args.fOutputCoverage);
 }
	/*
	* 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 "GrCCPathProcessor.h"

	#include "GrGpuCommandBuffer.h"
	#include "GrOnFlushResourceProvider.h"
	#include "GrTexture.h"
	#include "ccpr/GrCCPerFlushResources.h"
	#include "glsl/GrGLSLFragmentShaderBuilder.h"
	#include "glsl/GrGLSLGeometryProcessor.h"
	#include "glsl/GrGLSLProgramBuilder.h"
	#include "glsl/GrGLSLVarying.h"

	// Slightly undershoot an AA bloat radius of 0.5 so vertices that fall on integer boundaries don't
	// accidentally reach into neighboring path masks within the atlas.
	constexpr float kAABloatRadius = 0.491111f;

	// Paths are drawn as octagons. Each point on the octagon is the intersection of two lines: one edge
	// from the path's bounding box and one edge from its 45-degree bounding box. The below inputs
	// define a vertex by the two edges that need to be intersected. Normals point out of the octagon,
	// and the bounding boxes are sent in as instance attribs.
	static constexpr float kOctoEdgeNorms[8 * 4] = {
	// bbox // bbox45
	-1, 0, -1,+1,
	-1, 0, -1,-1,
	0,-1, -1,-1,
	0,-1, +1,-1,
	+1, 0, +1,-1,
	+1, 0, +1,+1,
	0,+1, +1,+1,
	0,+1, -1,+1,
	};

	GR_DECLARE_STATIC_UNIQUE_KEY(gVertexBufferKey);

	sk_sp<const GrBuffer> GrCCPathProcessor::FindVertexBuffer(GrOnFlushResourceProvider* onFlushRP) {
	GR_DEFINE_STATIC_UNIQUE_KEY(gVertexBufferKey);
	return onFlushRP->findOrMakeStaticBuffer(kVertex_GrBufferType, sizeof(kOctoEdgeNorms),
	kOctoEdgeNorms, gVertexBufferKey);
	}

	static constexpr uint16_t kRestartStrip = 0xffff;

	static constexpr uint16_t kOctoIndicesAsStrips[] = {
	1, 0, 2, 4, 3, kRestartStrip, // First half.
	5, 4, 6, 0, 7 // Second half.
	};

	static constexpr uint16_t kOctoIndicesAsTris[] = {
	// First half.
	1, 0, 2,
	0, 4, 2,
	2, 4, 3,

	// Second half.
	5, 4, 6,
	4, 0, 6,
	6, 0, 7,
	};

	GR_DECLARE_STATIC_UNIQUE_KEY(gIndexBufferKey);

	constexpr GrPrimitiveProcessor::Attribute GrCCPathProcessor::kInstanceAttribs[];
	constexpr GrPrimitiveProcessor::Attribute GrCCPathProcessor::kEdgeNormsAttrib;

	sk_sp<const GrBuffer> GrCCPathProcessor::FindIndexBuffer(GrOnFlushResourceProvider* onFlushRP) {
	GR_DEFINE_STATIC_UNIQUE_KEY(gIndexBufferKey);
	if (onFlushRP->caps()->usePrimitiveRestart()) {
	return onFlushRP->findOrMakeStaticBuffer(kIndex_GrBufferType, sizeof(kOctoIndicesAsStrips),
	kOctoIndicesAsStrips, gIndexBufferKey);
	} else {
	return onFlushRP->findOrMakeStaticBuffer(kIndex_GrBufferType, sizeof(kOctoIndicesAsTris),
	kOctoIndicesAsTris, gIndexBufferKey);
	}
	}

	GrCCPathProcessor::GrCCPathProcessor(GrResourceProvider* resourceProvider,
	sk_sp<GrTextureProxy> atlas,
	const SkMatrix& viewMatrixIfUsingLocalCoords)
	: INHERITED(kGrCCPathProcessor_ClassID)
	, fAtlasAccess(std::move(atlas), GrSamplerState::Filter::kNearest,
	GrSamplerState::WrapMode::kClamp, kFragment_GrShaderFlag) {
	this->setInstanceAttributeCnt(kNumInstanceAttribs);
	// Check that instance attributes exactly match Instance struct layout.
	SkASSERT(!strcmp(this->instanceAttribute(0).name(), "devbounds"));
	SkASSERT(!strcmp(this->instanceAttribute(1).name(), "devbounds45"));
	SkASSERT(!strcmp(this->instanceAttribute(2).name(), "dev_to_atlas_offset"));
	SkASSERT(!strcmp(this->instanceAttribute(3).name(), "color"));
	SkASSERT(this->debugOnly_instanceAttributeOffset(0) == offsetof(Instance, fDevBounds));
	SkASSERT(this->debugOnly_instanceAttributeOffset(1) == offsetof(Instance, fDevBounds45));
	SkASSERT(this->debugOnly_instanceAttributeOffset(2) == offsetof(Instance, fDevToAtlasOffset));
	SkASSERT(this->debugOnly_instanceAttributeOffset(3) == offsetof(Instance, fColor));
	SkASSERT(this->debugOnly_instanceStride() == sizeof(Instance));

	this->setVertexAttributeCnt(1);

	fAtlasAccess.instantiate(resourceProvider);
	this->addTextureSampler(&fAtlasAccess);

	if (!viewMatrixIfUsingLocalCoords.invert(&fLocalMatrix)) {
	fLocalMatrix.setIdentity();
	}
	}

	class GLSLPathProcessor : public GrGLSLGeometryProcessor {
	public:
	void onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) override;

	private:
	void setData(const GrGLSLProgramDataManager& pdman, const GrPrimitiveProcessor& primProc,
	FPCoordTransformIter&& transformIter) override {
	const GrCCPathProcessor& proc = primProc.cast<GrCCPathProcessor>();
	pdman.set2f(fAtlasAdjustUniform, 1.0f / proc.atlas()->width(),
	1.0f / proc.atlas()->height());
	this->setTransformDataHelper(proc.localMatrix(), pdman, &transformIter);
	}

	GrGLSLUniformHandler::UniformHandle fAtlasAdjustUniform;

	typedef GrGLSLGeometryProcessor INHERITED;
	};

	GrGLSLPrimitiveProcessor* GrCCPathProcessor::createGLSLInstance(const GrShaderCaps&) const {
	return new GLSLPathProcessor();
	}

	void GrCCPathProcessor::drawPaths(GrOpFlushState* flushState, const GrPipeline& pipeline,
	const GrCCPerFlushResources& resources, int baseInstance,
	int endInstance, const SkRect& bounds) const {
	const GrCaps& caps = flushState->caps();
	GrPrimitiveType primitiveType = caps.usePrimitiveRestart()
	? GrPrimitiveType::kTriangleStrip
	: GrPrimitiveType::kTriangles;
	int numIndicesPerInstance = caps.usePrimitiveRestart()
	? SK_ARRAY_COUNT(kOctoIndicesAsStrips)
	: SK_ARRAY_COUNT(kOctoIndicesAsTris);
	GrMesh mesh(primitiveType);
	auto enablePrimitiveRestart = GrPrimitiveRestart(flushState->caps().usePrimitiveRestart());

	mesh.setIndexedInstanced(resources.indexBuffer(), numIndicesPerInstance,
	resources.instanceBuffer(), endInstance - baseInstance, baseInstance,
	enablePrimitiveRestart);
	mesh.setVertexData(resources.vertexBuffer());

	flushState->rtCommandBuffer()->draw(*this, pipeline, &mesh, nullptr, 1, bounds);
	}

	void GLSLPathProcessor::onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) {
	using InstanceAttribs = GrCCPathProcessor::InstanceAttribs;
	using Interpolation = GrGLSLVaryingHandler::Interpolation;

	const GrCCPathProcessor& proc = args.fGP.cast<GrCCPathProcessor>();
	GrGLSLUniformHandler* uniHandler = args.fUniformHandler;
	GrGLSLVaryingHandler* varyingHandler = args.fVaryingHandler;

	const char* atlasAdjust;
	fAtlasAdjustUniform = uniHandler->addUniform(
	kVertex_GrShaderFlag,
	kFloat2_GrSLType, "atlas_adjust", &atlasAdjust);

	varyingHandler->emitAttributes(proc);

	GrGLSLVarying texcoord(kFloat3_GrSLType);
	GrGLSLVarying color(kHalf4_GrSLType);
	varyingHandler->addVarying("texcoord", &texcoord);
	varyingHandler->addPassThroughAttribute(proc.getInstanceAttrib(InstanceAttribs::kColor),
	args.fOutputColor, Interpolation::kCanBeFlat);

	// The vertex shader bloats and intersects the devBounds and devBounds45 rectangles, in order to
	// find an octagon that circumscribes the (bloated) path.
	GrGLSLVertexBuilder* v = args.fVertBuilder;

	// Each vertex is the intersection of one edge from devBounds and one from devBounds45.
	// 'N' holds the normals to these edges as column vectors.
	//
	// NOTE: "float2x2(float4)" is valid and equivalent to "float2x2(float4.xy, float4.zw)",
	// however Intel compilers crash when we use the former syntax in this shader.
	v->codeAppendf("float2x2 N = float2x2(%s.xy, %s.zw);", proc.getEdgeNormsAttrib().name(),
	proc.getEdgeNormsAttrib().name());

	// N[0] is the normal for the edge we are intersecting from the regular bounding box, pointing
	// out of the octagon.
	v->codeAppendf("float4 devbounds = %s;",
	proc.getInstanceAttrib(InstanceAttribs::kDevBounds).name());
	v->codeAppend ("float2 refpt = (0 == sk_VertexID >> 2)"
	"? float2(min(devbounds.x, devbounds.z), devbounds.y)"
	": float2(max(devbounds.x, devbounds.z), devbounds.w);");
	v->codeAppendf("refpt += N[0] * %f;", kAABloatRadius); // bloat for AA.

	// N[1] is the normal for the edge we are intersecting from the 45-degree bounding box, pointing
	// out of the octagon.
	v->codeAppendf("float2 refpt45 = (0 == ((sk_VertexID + 1) & (1 << 2))) ? %s.xy : %s.zw;",
	proc.getInstanceAttrib(InstanceAttribs::kDevBounds45).name(),
	proc.getInstanceAttrib(InstanceAttribs::kDevBounds45).name());
	v->codeAppendf("refpt45 *= float2x2(.5,.5,-.5,.5);"); // transform back to device space.
	v->codeAppendf("refpt45 += N[1] * %f;", kAABloatRadius); // bloat for AA.

	v->codeAppend ("float2 K = float2(dot(N[0], refpt), dot(N[1], refpt45));");
	v->codeAppendf("float2 octocoord = K * inverse(N);");

	gpArgs->fPositionVar.set(kFloat2_GrSLType, "octocoord");

	// Convert to atlas coordinates in order to do our texture lookup.
	v->codeAppendf("float2 atlascoord = octocoord + float2(%s);",
	proc.getInstanceAttrib(InstanceAttribs::kDevToAtlasOffset).name());
	if (kTopLeft_GrSurfaceOrigin == proc.atlasProxy()->origin()) {
	v->codeAppendf("%s.xy = atlascoord * %s;", texcoord.vsOut(), atlasAdjust);
	} else {
	SkASSERT(kBottomLeft_GrSurfaceOrigin == proc.atlasProxy()->origin());
	v->codeAppendf("%s.xy = float2(atlascoord.x * %s.x, 1 - atlascoord.y * %s.y);",
	texcoord.vsOut(), atlasAdjust, atlasAdjust);
	}
	// The third texture coordinate is -.5 for even-odd paths and +.5 for winding ones.
	// ("right < left" indicates even-odd fill type.)
	v->codeAppendf("%s.z = sign(devbounds.z - devbounds.x) * .5;", texcoord.vsOut());

	this->emitTransforms(v, varyingHandler, uniHandler, GrShaderVar("octocoord", kFloat2_GrSLType),
	proc.localMatrix(), args.fFPCoordTransformHandler);

	// Fragment shader.
	GrGLSLFPFragmentBuilder* f = args.fFragBuilder;

	// Look up coverage count in the atlas.
	f->codeAppend ("half coverage = ");
	f->appendTextureLookup(args.fTexSamplers[0], SkStringPrintf("%s.xy", texcoord.fsIn()).c_str(),
	kFloat2_GrSLType);
	f->codeAppend (".a;");

	// Scale coverage count by .5. Make it negative for even-odd paths and positive for winding
	// ones. Clamp winding coverage counts at 1.0 (i.e. min(coverage/2, .5)).
	f->codeAppendf("coverage = min(abs(coverage) * %s.z, .5);", texcoord.fsIn());

	// For negative values, this finishes the even-odd sawtooth function. Since positive (winding)
	// values were clamped at "coverage/2 = .5", this only undoes the previous multiply by .5.
	f->codeAppend ("coverage = 1 - abs(fract(coverage) * 2 - 1);");

	f->codeAppendf("%s = half4(coverage);", args.fOutputCoverage);
	}