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 "GrOnFlushResourceProvider.h"
 #include "GrTexture.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);

 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);
     }
 }

 int GrCCPathProcessor::NumIndicesPerInstance(const GrCaps& caps) {
     return caps.usePrimitiveRestart() ? SK_ARRAY_COUNT(kOctoIndicesAsStrips)
                                       : SK_ARRAY_COUNT(kOctoIndicesAsTris);
 }

 GrCCPathProcessor::GrCCPathProcessor(GrResourceProvider* resourceProvider,
                                      sk_sp<GrTextureProxy> atlas, SkPath::FillType fillType)
         : INHERITED(kGrCCPathProcessor_ClassID)
         , fFillType(fillType)
         , fAtlasAccess(std::move(atlas), GrSamplerState::Filter::kNearest,
                        GrSamplerState::WrapMode::kClamp, kFragment_GrShaderFlag) {
     this->addInstanceAttrib("devbounds", kFloat4_GrVertexAttribType);
     this->addInstanceAttrib("devbounds45", kFloat4_GrVertexAttribType);
     this->addInstanceAttrib("view_matrix", kFloat4_GrVertexAttribType);
     this->addInstanceAttrib("view_translate", kFloat2_GrVertexAttribType);
     this->addInstanceAttrib("atlas_offset", kShort2_GrVertexAttribType);
     this->addInstanceAttrib("color", kUByte4_norm_GrVertexAttribType);

     SkASSERT(offsetof(Instance, fDevBounds) ==
              this->getInstanceAttrib(InstanceAttribs::kDevBounds).fOffsetInRecord);
     SkASSERT(offsetof(Instance, fDevBounds45) ==
              this->getInstanceAttrib(InstanceAttribs::kDevBounds45).fOffsetInRecord);
     SkASSERT(offsetof(Instance, fViewMatrix) ==
              this->getInstanceAttrib(InstanceAttribs::kViewMatrix).fOffsetInRecord);
     SkASSERT(offsetof(Instance, fViewTranslate) ==
              this->getInstanceAttrib(InstanceAttribs::kViewTranslate).fOffsetInRecord);
     SkASSERT(offsetof(Instance, fAtlasOffset) ==
              this->getInstanceAttrib(InstanceAttribs::kAtlasOffset).fOffsetInRecord);
     SkASSERT(offsetof(Instance, fColor) ==
              this->getInstanceAttrib(InstanceAttribs::kColor).fOffsetInRecord);
     SkASSERT(sizeof(Instance) == this->getInstanceStride());

     GR_STATIC_ASSERT(6 == kNumInstanceAttribs);

     this->addVertexAttrib("edge_norms", kFloat4_GrVertexAttribType);

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

     if (resourceProvider->caps()->usePrimitiveRestart()) {
         this->setWillUsePrimitiveRestart();
     }
 }

 void GrCCPathProcessor::getGLSLProcessorKey(const GrShaderCaps&, GrProcessorKeyBuilder* b) const {
     b->add32((fFillType << 16) | this->atlasProxy()->origin());
 }

 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(SkMatrix::I(), pdman, &transformIter);
     }

     GrGLSLUniformHandler::UniformHandle fAtlasAdjustUniform;

     typedef GrGLSLGeometryProcessor INHERITED;
 };

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

 void GLSLPathProcessor::onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) {
     using InstanceAttribs = GrCCPathProcessor::InstanceAttribs;
     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(kFloat2_GrSLType);
     GrGLSLVarying color(kHalf4_GrSLType);
     varyingHandler->addVarying("texcoord", &texcoord);
     varyingHandler->addFlatPassThroughAttribute(&proc.getInstanceAttrib(InstanceAttribs::kColor),
                                                 args.fOutputColor);

     // 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().fName, proc.getEdgeNormsAttrib().fName);

     // N[0] is the normal for the edge we are intersecting from the regular bounding box, pointing
     // out of the octagon.
     v->codeAppendf("float2 refpt = float2[2](%s.xy, %s.zw)[sk_VertexID >> 2];",
                    proc.getInstanceAttrib(InstanceAttribs::kDevBounds).fName,
                    proc.getInstanceAttrib(InstanceAttribs::kDevBounds).fName);
     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 = float2[2](%s.xy, %s.zw)[((sk_VertexID + 1) >> 2) & 1];",
                    proc.getInstanceAttrib(InstanceAttribs::kDevBounds45).fName,
                    proc.getInstanceAttrib(InstanceAttribs::kDevBounds45).fName);
     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::kAtlasOffset).fName);
     if (kTopLeft_GrSurfaceOrigin == proc.atlasProxy()->origin()) {
         v->codeAppendf("%s = atlascoord * %s;", texcoord.vsOut(), atlasAdjust);
     } else {
         SkASSERT(kBottomLeft_GrSurfaceOrigin == proc.atlasProxy()->origin());
         v->codeAppendf("%s = float2(atlascoord.x * %s.x, 1 - atlascoord.y * %s.y);",
                        texcoord.vsOut(), atlasAdjust, atlasAdjust);
     }

     // Convert to path/local cordinates.
     v->codeAppendf("float2x2 viewmatrix = float2x2(%s.xy, %s.zw);", // float2x2(float4) busts Intel.
                    proc.getInstanceAttrib(InstanceAttribs::kViewMatrix).fName,
                    proc.getInstanceAttrib(InstanceAttribs::kViewMatrix).fName);
     v->codeAppendf("float2 pathcoord = inverse(viewmatrix) * (octocoord - %s);",
                    proc.getInstanceAttrib(InstanceAttribs::kViewTranslate).fName);

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

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

     f->codeAppend ("half coverage_count = ");
     f->appendTextureLookup(args.fTexSamplers[0], texcoord.fsIn(), kFloat2_GrSLType);
     f->codeAppend (".a;");

     if (SkPath::kWinding_FillType == proc.fillType()) {
         f->codeAppendf("%s = half4(min(abs(coverage_count), 1));", args.fOutputCoverage);
     } else {
         SkASSERT(SkPath::kEvenOdd_FillType == proc.fillType());
         f->codeAppend ("half t = mod(abs(coverage_count), 2);");
         f->codeAppendf("%s = half4(1 - abs(t - 1));", 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 "GrOnFlushResourceProvider.h"
	#include "GrTexture.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);

	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);
	}
	}

	int GrCCPathProcessor::NumIndicesPerInstance(const GrCaps& caps) {
	return caps.usePrimitiveRestart() ? SK_ARRAY_COUNT(kOctoIndicesAsStrips)
	: SK_ARRAY_COUNT(kOctoIndicesAsTris);
	}

	GrCCPathProcessor::GrCCPathProcessor(GrResourceProvider* resourceProvider,
	sk_sp<GrTextureProxy> atlas, SkPath::FillType fillType)
	: INHERITED(kGrCCPathProcessor_ClassID)
	, fFillType(fillType)
	, fAtlasAccess(std::move(atlas), GrSamplerState::Filter::kNearest,
	GrSamplerState::WrapMode::kClamp, kFragment_GrShaderFlag) {
	this->addInstanceAttrib("devbounds", kFloat4_GrVertexAttribType);
	this->addInstanceAttrib("devbounds45", kFloat4_GrVertexAttribType);
	this->addInstanceAttrib("view_matrix", kFloat4_GrVertexAttribType);
	this->addInstanceAttrib("view_translate", kFloat2_GrVertexAttribType);
	this->addInstanceAttrib("atlas_offset", kShort2_GrVertexAttribType);
	this->addInstanceAttrib("color", kUByte4_norm_GrVertexAttribType);

	SkASSERT(offsetof(Instance, fDevBounds) ==
	this->getInstanceAttrib(InstanceAttribs::kDevBounds).fOffsetInRecord);
	SkASSERT(offsetof(Instance, fDevBounds45) ==
	this->getInstanceAttrib(InstanceAttribs::kDevBounds45).fOffsetInRecord);
	SkASSERT(offsetof(Instance, fViewMatrix) ==
	this->getInstanceAttrib(InstanceAttribs::kViewMatrix).fOffsetInRecord);
	SkASSERT(offsetof(Instance, fViewTranslate) ==
	this->getInstanceAttrib(InstanceAttribs::kViewTranslate).fOffsetInRecord);
	SkASSERT(offsetof(Instance, fAtlasOffset) ==
	this->getInstanceAttrib(InstanceAttribs::kAtlasOffset).fOffsetInRecord);
	SkASSERT(offsetof(Instance, fColor) ==
	this->getInstanceAttrib(InstanceAttribs::kColor).fOffsetInRecord);
	SkASSERT(sizeof(Instance) == this->getInstanceStride());

	GR_STATIC_ASSERT(6 == kNumInstanceAttribs);

	this->addVertexAttrib("edge_norms", kFloat4_GrVertexAttribType);

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

	if (resourceProvider->caps()->usePrimitiveRestart()) {
	this->setWillUsePrimitiveRestart();
	}
	}

	void GrCCPathProcessor::getGLSLProcessorKey(const GrShaderCaps&, GrProcessorKeyBuilder* b) const {
	b->add32((fFillType << 16) \| this->atlasProxy()->origin());
	}

	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(SkMatrix::I(), pdman, &transformIter);
	}

	GrGLSLUniformHandler::UniformHandle fAtlasAdjustUniform;

	typedef GrGLSLGeometryProcessor INHERITED;
	};

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

	void GLSLPathProcessor::onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) {
	using InstanceAttribs = GrCCPathProcessor::InstanceAttribs;
	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(kFloat2_GrSLType);
	GrGLSLVarying color(kHalf4_GrSLType);
	varyingHandler->addVarying("texcoord", &texcoord);
	varyingHandler->addFlatPassThroughAttribute(&proc.getInstanceAttrib(InstanceAttribs::kColor),
	args.fOutputColor);

	// 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().fName, proc.getEdgeNormsAttrib().fName);

	// N[0] is the normal for the edge we are intersecting from the regular bounding box, pointing
	// out of the octagon.
	v->codeAppendf("float2 refpt = float2[2](%s.xy, %s.zw)[sk_VertexID >> 2];",
	proc.getInstanceAttrib(InstanceAttribs::kDevBounds).fName,
	proc.getInstanceAttrib(InstanceAttribs::kDevBounds).fName);
	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 = float2[2](%s.xy, %s.zw)[((sk_VertexID + 1) >> 2) & 1];",
	proc.getInstanceAttrib(InstanceAttribs::kDevBounds45).fName,
	proc.getInstanceAttrib(InstanceAttribs::kDevBounds45).fName);
	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::kAtlasOffset).fName);
	if (kTopLeft_GrSurfaceOrigin == proc.atlasProxy()->origin()) {
	v->codeAppendf("%s = atlascoord * %s;", texcoord.vsOut(), atlasAdjust);
	} else {
	SkASSERT(kBottomLeft_GrSurfaceOrigin == proc.atlasProxy()->origin());
	v->codeAppendf("%s = float2(atlascoord.x * %s.x, 1 - atlascoord.y * %s.y);",
	texcoord.vsOut(), atlasAdjust, atlasAdjust);
	}

	// Convert to path/local cordinates.
	v->codeAppendf("float2x2 viewmatrix = float2x2(%s.xy, %s.zw);", // float2x2(float4) busts Intel.
	proc.getInstanceAttrib(InstanceAttribs::kViewMatrix).fName,
	proc.getInstanceAttrib(InstanceAttribs::kViewMatrix).fName);
	v->codeAppendf("float2 pathcoord = inverse(viewmatrix) * (octocoord - %s);",
	proc.getInstanceAttrib(InstanceAttribs::kViewTranslate).fName);

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

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

	f->codeAppend ("half coverage_count = ");
	f->appendTextureLookup(args.fTexSamplers[0], texcoord.fsIn(), kFloat2_GrSLType);
	f->codeAppend (".a;");

	if (SkPath::kWinding_FillType == proc.fillType()) {
	f->codeAppendf("%s = half4(min(abs(coverage_count), 1));", args.fOutputCoverage);
	} else {
	SkASSERT(SkPath::kEvenOdd_FillType == proc.fillType());
	f->codeAppend ("half t = mod(abs(coverage_count), 2);");
	f->codeAppendf("%s = half4(1 - abs(t - 1));", args.fOutputCoverage);
	}
	}