GrStrokeTessellationShader::Impl Class Reference

Inheritance diagram for GrStrokeTessellationShader::Impl:

Private Member Functions
void	onEmitCode (EmitArgs &, GrGPArgs *) override
void	setData (const GrGLSLProgramDataManager &pdman, const GrShaderCaps &, const GrGeometryProcessor &) final

Additional Inherited Members
Public Types inherited from GrFragmentProcessor::ProgramImpl
using	UniformHandle = GrGLSLUniformHandler::UniformHandle
using	SamplerHandle = GrGLSLUniformHandler::SamplerHandle
Public Member Functions inherited from GrFragmentProcessor::ProgramImpl
	ProgramImpl ()=default
virtual	~ProgramImpl ()=default
virtual void	emitCode (EmitArgs &)=0
void	setData (const GrGLSLProgramDataManager &pdman, const GrFragmentProcessor &processor)
int	numChildProcessors () const
ProgramImpl *	childProcessor (int index) const
void	setFunctionName (SkString name)
const char *	functionName () const
SkString	invokeChild (int childIndex, EmitArgs &parentArgs, std::string_view skslCoords={})
SkString	invokeChildWithMatrix (int childIndex, EmitArgs &parentArgs)
SkString	invokeChild (int childIndex, const char *inputColor, EmitArgs &parentArgs, std::string_view skslCoords={})
SkString	invokeChildWithMatrix (int childIndex, const char *inputColor, EmitArgs &parentArgs)
SkString	invokeChild (int childIndex, const char *inputColor, const char *destColor, EmitArgs &parentArgs, std::string_view skslCoords={})
SkString	invokeChildWithMatrix (int childIndex, const char *inputColor, const char *destColor, EmitArgs &parentArgs)

Detailed Description

Definition at line 142 of file GrStrokeTessellationShader.cpp.

Member Function Documentation

onEmitCode()

void GrStrokeTessellationShader::Impl::onEmitCode ( EmitArgs &  args, GrGPArgs *  gpArgs  )

overrideprivate

Definition at line 185 of file GrStrokeTessellationShader.cpp.

                                                                                {
    const auto& shader = args.fGeomProc.cast<GrStrokeTessellationShader>();
    SkPaint::Join joinType = shader.stroke().getJoin();
    args.fVaryingHandler->emitAttributes(shader);
 
    args.fVertBuilder->defineConstant("float", "PI", "3.141592653589793238");
    args.fVertBuilder->defineConstant("PRECISION", skgpu::tess::kPrecision);
    // There is an artificial maximum number of edges (compared to the max limit calculated based on
    // the number of radial segments per radian, Wang's formula, and join type). When there is
    // vertex ID support, the limit is what can be represented in a uint16; otherwise the limit is
    // the size of the fallback vertex buffer.
    float maxEdges = args.fShaderCaps->fVertexIDSupport ? FixedCountStrokes::kMaxEdges
                                                        : FixedCountStrokes::kMaxEdgesNoVertexIDs;
    args.fVertBuilder->defineConstant("NUM_TOTAL_EDGES", maxEdges);
 
    // Helper functions.
    if (shader.hasDynamicStroke()) {
        args.fVertBuilder->insertFunction(kNumRadialSegmentsPerRadianFn);
    }
    args.fVertBuilder->insertFunction(kRobustNormalizeDiffFn);
    args.fVertBuilder->insertFunction(kCosineBetweenUnitVectorsFn);
    args.fVertBuilder->insertFunction(kMiterExtentFn);
    args.fVertBuilder->insertFunction(kUncheckedMixFn);
    args.fVertBuilder->insertFunction(GrTessellationShader::WangsFormulaSkSL());
 
    // Tessellation control uniforms and/or dynamic attributes.
    if (!shader.hasDynamicStroke()) {
        // [NUM_RADIAL_SEGMENTS_PER_RADIAN, JOIN_TYPE, STROKE_RADIUS]
        const char* tessArgsName;
        fTessControlArgsUniform = args.fUniformHandler->addUniform(
                nullptr, kVertex_GrShaderFlag, SkSLType::kFloat3, "tessControlArgs",
                &tessArgsName);
        args.fVertBuilder->codeAppendf(
        "float NUM_RADIAL_SEGMENTS_PER_RADIAN = %s.x;"
        "float JOIN_TYPE = %s.y;"
        "float STROKE_RADIUS = %s.z;", tessArgsName, tessArgsName, tessArgsName);
    } else {
        // The shader does not currently support dynamic hairlines, so this case only needs to
        // configure NUM_RADIAL_SEGMENTS_PER_RADIAN based on the fixed maxScale and per-instance
        // stroke radius attribute that's defined in local space.
        SkASSERT(!shader.stroke().isHairlineStyle());
        const char* maxScaleName;
        fTessControlArgsUniform = args.fUniformHandler->addUniform(
                nullptr, kVertex_GrShaderFlag, SkSLType::kFloat, "maxScale",
                &maxScaleName);
        args.fVertBuilder->codeAppendf(
        "float STROKE_RADIUS = dynamicStrokeAttr.x;"
        "float JOIN_TYPE = dynamicStrokeAttr.y;"
        "float NUM_RADIAL_SEGMENTS_PER_RADIAN = num_radial_segments_per_radian("
                "%s * STROKE_RADIUS);", maxScaleName);
 
    }
 
    if (shader.hasDynamicColor()) {
        // Create a varying for color to get passed in through.
        GrGLSLVarying dynamicColor{SkSLType::kHalf4};
        args.fVaryingHandler->addVarying("dynamicColor", &dynamicColor);
        args.fVertBuilder->codeAppendf("%s = dynamicColorAttr;", dynamicColor.vsOut());
        fDynamicColorName = dynamicColor.fsIn();
    }
 
    // View matrix uniforms.
    const char* translateName, *affineMatrixName;
    fAffineMatrixUniform = args.fUniformHandler->addUniform(nullptr, kVertex_GrShaderFlag,
                                                            SkSLType::kFloat4, "affineMatrix",
                                                            &affineMatrixName);
    fTranslateUniform = args.fUniformHandler->addUniform(nullptr, kVertex_GrShaderFlag,
                                                         SkSLType::kFloat2, "translate",
                                                         &translateName);
    args.fVertBuilder->codeAppendf("float2x2 AFFINE_MATRIX = float2x2(%s.xy, %s.zw);\n",
                                   affineMatrixName, affineMatrixName);
    args.fVertBuilder->codeAppendf("float2 TRANSLATE = %s;\n", translateName);
 
    if (shader.hasExplicitCurveType()) {
        args.fVertBuilder->insertFunction(SkStringPrintf(
        "bool is_conic_curve() { return curveTypeAttr != %g; }",
            skgpu::tess::kCubicCurveType).c_str());
    } else {
        args.fVertBuilder->insertFunction(
        "bool is_conic_curve() { return isinf(pts23Attr.w); }");
    }
 
    // Tessellation code.
    args.fVertBuilder->codeAppend(
    "float2 p0=pts01Attr.xy, p1=pts01Attr.zw, p2=pts23Attr.xy, p3=pts23Attr.zw;"
    "float2 lastControlPoint = argsAttr.xy;"
    "float w = -1;"  // w<0 means the curve is an integral cubic.
    "if (is_conic_curve()) {"
        // Conics are 3 points, with the weight in p3.
        "w = p3.x;"
        "p3 = p2;"  // Setting p3 equal to p2 works for the remaining rotational logic.
    "}"
    );
 
    // Emit code to call Wang's formula to determine parametric segments. We do this before
    // transform points for hairlines so that it is consistent with how the CPU tested the control
    // points for chopping.
    args.fVertBuilder->codeAppend(
    // Find how many parametric segments this stroke requires.
    "float numParametricSegments;"
    "if (w < 0) {"
        "if (p0 == p1 && p2 == p3) {"
            "numParametricSegments = 1;" // a line
        "} else {"
            "numParametricSegments = wangs_formula_cubic(PRECISION, p0, p1, p2, p3, AFFINE_MATRIX);"
        "}"
    "} else {"
        "numParametricSegments = wangs_formula_conic(PRECISION,"
                                                    "AFFINE_MATRIX * p0,"
                                                    "AFFINE_MATRIX * p1,"
                                                    "AFFINE_MATRIX * p2, w);"
    "}"
    );
 
    if (shader.stroke().isHairlineStyle()) {
        // Hairline case. Transform the points before tessellation. We can still hold off on the
        // translate until the end; we just need to perform the scale and skew right now.
        args.fVertBuilder->codeAppend(
        "p0 = AFFINE_MATRIX * p0;"
        "p1 = AFFINE_MATRIX * p1;"
        "p2 = AFFINE_MATRIX * p2;"
        "p3 = AFFINE_MATRIX * p3;"
        "lastControlPoint = AFFINE_MATRIX * lastControlPoint;"
        );
    }
 
    args.fVertBuilder->codeAppend(
    // Find the starting and ending tangents.
    "float2 tan0 = robust_normalize_diff((p0 == p1) ? ((p1 == p2) ? p3 : p2) : p1, p0);"
    "float2 tan1 = robust_normalize_diff(p3, (p3 == p2) ? ((p2 == p1) ? p0 : p1) : p2);"
    "if (tan0 == float2(0)) {"
        // The stroke is a point. This special case tells us to draw a stroke-width circle as a
        // 180 degree point stroke instead.
        "tan0 = float2(1,0);"
        "tan1 = float2(-1,0);"
    "}"
    );
 
    if (args.fShaderCaps->fVertexIDSupport) {
        // If we don't have sk_VertexID support then "edgeID" already came in as a vertex attrib.
        args.fVertBuilder->codeAppend(
        "float edgeID = float(sk_VertexID >> 1);"
        "if ((sk_VertexID & 1) != 0) {"
            "edgeID = -edgeID;"
        "}"
        );
    }
 
    // Potential optimization: (shader.hasDynamicStroke() && shader.hasRoundJoins())?
    if (shader.stroke().getJoin() == SkPaint::kRound_Join || shader.hasDynamicStroke()) {
        args.fVertBuilder->codeAppend(
        // Determine how many edges to give to the round join. We emit the first and final edges
        // of the join twice: once full width and once restricted to half width. This guarantees
        // perfect seaming by matching the vertices from the join as well as from the strokes on
        // either side.
        "float2 prevTan = robust_normalize_diff(p0, lastControlPoint);"
        "float joinRads = acos(cosine_between_unit_vectors(prevTan, tan0));"
        "float numRadialSegmentsInJoin = max(ceil(joinRads * NUM_RADIAL_SEGMENTS_PER_RADIAN), 1);"
        // +2 because we emit the beginning and ending edges twice (see above comment).
        "float numEdgesInJoin = numRadialSegmentsInJoin + 2;"
        // The stroke section needs at least two edges. Don't assign more to the join than
        // "NUM_TOTAL_EDGES - 2". (This is only relevant when the ideal max edge count calculated
        // on the CPU had to be limited to NUM_TOTAL_EDGES in the draw call).
        "numEdgesInJoin = min(numEdgesInJoin, NUM_TOTAL_EDGES - 2);");
        if (shader.hasDynamicStroke()) {
            args.fVertBuilder->codeAppend(
            "if (JOIN_TYPE >= 0) {" // Is the join not a round type?
                // Bevel and miter joins get 1 and 2 segments respectively.
                // +2 because we emit the beginning and ending edges twice (see above comments).
                "numEdgesInJoin = sign(JOIN_TYPE) + 1 + 2;"
            "}");
        }
    } else {
        args.fVertBuilder->codeAppendf("float numEdgesInJoin = %i;",
        skgpu::tess::NumFixedEdgesInJoin(joinType));
    }
 
    args.fVertBuilder->codeAppend(
    // Find which direction the curve turns.
    // NOTE: Since the curve is not allowed to inflect, we can just check F'(.5) x F''(.5).
    // NOTE: F'(.5) x F''(.5) has the same sign as (P2 - P0) x (P3 - P1)
    "float turn = cross_length_2d(p2 - p0, p3 - p1);"
    "float combinedEdgeID = abs(edgeID) - numEdgesInJoin;"
    "if (combinedEdgeID < 0) {"
        "tan1 = tan0;"
        // Don't let tan0 become zero. The code as-is isn't built to handle that case. tan0=0
        // means the join is disabled, and to disable it with the existing code we can leave
        // tan0 equal to tan1.
        "if (lastControlPoint != p0) {"
            "tan0 = robust_normalize_diff(p0, lastControlPoint);"
        "}"
        "turn = cross_length_2d(tan0, tan1);"
    "}"
 
    // Calculate the curve's starting angle and rotation.
    "float cosTheta = cosine_between_unit_vectors(tan0, tan1);"
    "float rotation = acos(cosTheta);"
    "if (turn < 0) {"
        // Adjust sign of rotation to match the direction the curve turns.
        "rotation = -rotation;"
    "}"
 
    "float numRadialSegments;"
    "float strokeOutset = sign(edgeID);"
    "if (combinedEdgeID < 0) {"
        // We belong to the preceding join. The first and final edges get duplicated, so we only
        // have "numEdgesInJoin - 2" segments.
        "numRadialSegments = numEdgesInJoin - 2;"
        "numParametricSegments = 1;"  // Joins don't have parametric segments.
        "p3 = p2 = p1 = p0;"  // Colocate all points on the junction point.
        // Shift combinedEdgeID to the range [-1, numRadialSegments]. This duplicates the first
        // edge and lands one edge at the very end of the join. (The duplicated final edge will
        // actually come from the section of our strip that belongs to the stroke.)
        "combinedEdgeID += numRadialSegments + 1;"
        // We normally restrict the join on one side of the junction, but if the tangents are
        // nearly equivalent this could theoretically result in bad seaming and/or cracks on the
        // side we don't put it on. If the tangents are nearly equivalent then we leave the join
        // double-sided.
       " float sinEpsilon = 1e-2;"  // ~= sin(180deg / 3000)
        "bool tangentsNearlyParallel ="
                "(abs(turn) * inversesqrt(dot(tan0, tan0) * dot(tan1, tan1))) < sinEpsilon;"
        "if (!tangentsNearlyParallel || dot(tan0, tan1) < 0) {"
            // There are two edges colocated at the beginning. Leave the first one double sided
            // for seaming with the previous stroke. (The double sided edge at the end will
            // actually come from the section of our strip that belongs to the stroke.)
            "if (combinedEdgeID >= 0) {"
                "strokeOutset = (turn < 0) ? min(strokeOutset, 0) : max(strokeOutset, 0);"
            "}"
        "}"
        "combinedEdgeID = max(combinedEdgeID, 0);"
    "} else {"
        // We belong to the stroke. Unless NUM_RADIAL_SEGMENTS_PER_RADIAN is incredibly high,
        // clamping to maxCombinedSegments will be a no-op because the draw call was invoked with
        // sufficient vertices to cover the worst case scenario of 180 degree rotation.
        "float maxCombinedSegments = NUM_TOTAL_EDGES - numEdgesInJoin - 1;"
        "numRadialSegments = max(ceil(abs(rotation) * NUM_RADIAL_SEGMENTS_PER_RADIAN), 1);"
        "numRadialSegments = min(numRadialSegments, maxCombinedSegments);"
        "numParametricSegments = min(numParametricSegments,"
                                    "maxCombinedSegments - numRadialSegments + 1);"
    "}"
 
    // Additional parameters for emitTessellationCode().
    "float radsPerSegment = rotation / numRadialSegments;"
    "float numCombinedSegments = numParametricSegments + numRadialSegments - 1;"
    "bool isFinalEdge = (combinedEdgeID >= numCombinedSegments);"
    "if (combinedEdgeID > numCombinedSegments) {"
        "strokeOutset = 0;"  // The strip has more edges than we need. Drop this one.
    "}");
 
    if (joinType == SkPaint::kMiter_Join || shader.hasDynamicStroke()) {
        args.fVertBuilder->codeAppendf(
        // Edge #2 extends to the miter point.
        "if (abs(edgeID) == 2 && %s) {"
            "strokeOutset *= miter_extent(cosTheta, JOIN_TYPE);" // miterLimit
        "}", shader.hasDynamicStroke() ? "JOIN_TYPE > 0" /*Is the join a miter type?*/ : "true");
    }
 
    this->emitTessellationCode(shader, &args.fVertBuilder->code(), gpArgs, *args.fShaderCaps);
 
    this->emitFragmentCode(shader, args);
}

setData()

void GrStrokeTessellationShader::Impl::setData ( const GrGLSLProgramDataManager &  pdman, const GrShaderCaps &  , const GrGeometryProcessor &  geomProc  )

finalprivate

Definition at line 657 of file GrStrokeTessellationShader.cpp.

                                                                                    {
    const auto& shader = geomProc.cast<GrStrokeTessellationShader>();
    const auto& stroke = shader.stroke();
 
    // getMaxScale() returns -1 if it can't compute a scale factor (e.g. perspective), taking the
    // absolute value automatically converts that to an identity scale factor for our purposes.
    const float maxScale = std::abs(shader.viewMatrix().getMaxScale());
    if (!shader.hasDynamicStroke()) {
        // Set up the tessellation control uniforms. In the hairline case we transform prior to
        // tessellation, so it will be defined in device space units instead of local units.
        const float strokeRadius = 0.5f * (stroke.isHairlineStyle() ? 1.f : stroke.getWidth());
        float numRadialSegmentsPerRadian = skgpu::tess::CalcNumRadialSegmentsPerRadian(
                (stroke.isHairlineStyle() ? 1.f : maxScale) * strokeRadius);
 
        pdman.set3f(fTessControlArgsUniform,
                    numRadialSegmentsPerRadian,  // NUM_RADIAL_SEGMENTS_PER_RADIAN
                    skgpu::tess::GetJoinType(stroke),  // JOIN_TYPE
                    strokeRadius);  // STROKE_RADIUS
    } else {
        SkASSERT(!stroke.isHairlineStyle());
        pdman.set1f(fTessControlArgsUniform, maxScale);
    }
 
    // Set up the view matrix, if any.
    const SkMatrix& m = shader.viewMatrix();
    pdman.set2f(fTranslateUniform, m.getTranslateX(), m.getTranslateY());
    pdman.set4f(fAffineMatrixUniform, m.getScaleX(), m.getSkewY(), m.getSkewX(),
                m.getScaleY());
 
    if (!shader.hasDynamicColor()) {
        pdman.set4fv(fColorUniform, 1, shader.color().vec());
    }
}

---

The documentation for this class was generated from the following file:

• third_party/skia/src/gpu/ganesh/tessellate/GrStrokeTessellationShader.cpp