| /* |
| * Copyright 2020 Google LLC. |
| * |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| */ |
| |
| #include "src/gpu/ganesh/tessellate/GrStrokeTessellationShader.h" |
| |
| #include "src/gpu/KeyBuilder.h" |
| #include "src/gpu/ganesh/glsl/GrGLSLFragmentShaderBuilder.h" |
| #include "src/gpu/ganesh/glsl/GrGLSLVarying.h" |
| #include "src/gpu/ganesh/glsl/GrGLSLVertexGeoBuilder.h" |
| #include "src/gpu/tessellate/FixedCountBufferUtils.h" |
| #include "src/gpu/tessellate/WangsFormula.h" |
| |
| namespace { |
| |
| // float2 robust_normalize_diff(float2 a, float b) { ... } |
| // |
| // Returns the normalized difference between a and b, i.e. normalize(a - b), with care taken for |
| // if 'a' and/or 'b' have large coordinates. |
| static const char* kRobustNormalizeDiffFn = R"( |
| float2 robust_normalize_diff(float2 a, float2 b) { |
| float2 diff = a - b; |
| if (diff == float2(0.0)) { |
| return float2(0.0); |
| } else { |
| float invMag = 1.0 / max(abs(diff.x), abs(diff.y)); |
| return normalize(invMag * diff); |
| } |
| })"; |
| |
| // float cosine_between_unit_vectors(float2 a, float2 b) { ... |
| // |
| // Returns the cosine of the angle between a and b, assuming a and b are unit vectors already. |
| // Guaranteed to be between [-1, 1]. |
| static const char* kCosineBetweenUnitVectorsFn = R"( |
| float cosine_between_unit_vectors(float2 a, float2 b) { |
| // Since a and b are assumed to be normalized, the cosine is equal to the dot product, although |
| // we clamp that to ensure it falls within the expected range of [-1, 1]. |
| return clamp(dot(a, b), -1.0, 1.0); |
| })"; |
| |
| |
| // float miter_extent(float cosTheta, float miterLimit) { ... |
| // |
| // Extends the middle radius to either the miter point, or the bevel edge if we surpassed the |
| // miter limit and need to revert to a bevel join. |
| static const char* kMiterExtentFn = R"( |
| float miter_extent(float cosTheta, float miterLimit) { |
| float x = fma(cosTheta, .5, .5); |
| return (x * miterLimit * miterLimit >= 1.0) ? inversesqrt(x) : sqrt(x); |
| })"; |
| |
| // float num_radial_segments_per_radian(float approxDevStrokeRadius) { ... |
| // |
| // Returns the number of radial segments required for each radian of rotation, in order for the |
| // curve to appear "smooth" as defined by the approximate device-space stroke radius. |
| static const char* kNumRadialSegmentsPerRadianFn = R"( |
| float num_radial_segments_per_radian(float approxDevStrokeRadius) { |
| return .5 / acos(max(1.0 - (1.0 / PRECISION) / approxDevStrokeRadius, -1.0)); |
| })"; |
| |
| // float<N> unchecked_mix(float<N> a, float<N> b, float<N> T) { ... |
| // |
| // Unlike mix(), this does not return b when t==1. But it otherwise seems to get better |
| // precision than "a*(1 - t) + b*t" for things like chopping cubics on exact cusp points. |
| // We override this result anyway when t==1 so it shouldn't be a problem. |
| static const char* kUncheckedMixFn = R"( |
| float unchecked_mix(float a, float b, float T) { |
| return fma(b - a, T, a); |
| } |
| float2 unchecked_mix(float2 a, float2 b, float T) { |
| return fma(b - a, float2(T), a); |
| } |
| float4 unchecked_mix(float4 a, float4 b, float4 T) { |
| return fma(b - a, T, a); |
| })"; |
| |
| using skgpu::tess::FixedCountStrokes; |
| |
| } // anonymous namespace |
| |
| GrStrokeTessellationShader::GrStrokeTessellationShader(const GrShaderCaps& shaderCaps, |
| PatchAttribs attribs, |
| const SkMatrix& viewMatrix, |
| const SkStrokeRec& stroke, |
| SkPMColor4f color) |
| : GrTessellationShader(kTessellate_GrStrokeTessellationShader_ClassID, |
| GrPrimitiveType::kTriangleStrip, viewMatrix, color) |
| , fPatchAttribs(attribs | PatchAttribs::kJoinControlPoint) |
| , fStroke(stroke) { |
| // We should use explicit curve type when, and only when, there isn't infinity support. |
| // Otherwise the GPU can infer curve type based on infinity. |
| SkASSERT(shaderCaps.infinitySupport() != (attribs & PatchAttribs::kExplicitCurveType)); |
| // pts 0..3 define the stroke as a cubic bezier. If p3.y is infinity, then it's a conic |
| // with w=p3.x. |
| // |
| // An empty stroke (p0==p1==p2==p3) is a special case that denotes a circle, or |
| // 180-degree point stroke. |
| fAttribs.emplace_back("pts01Attr", kFloat4_GrVertexAttribType, SkSLType::kFloat4); |
| fAttribs.emplace_back("pts23Attr", kFloat4_GrVertexAttribType, SkSLType::kFloat4); |
| |
| // argsAttr contains the lastControlPoint for setting up the join. |
| fAttribs.emplace_back("argsAttr", kFloat2_GrVertexAttribType, SkSLType::kFloat2); |
| |
| if (fPatchAttribs & PatchAttribs::kStrokeParams) { |
| fAttribs.emplace_back("dynamicStrokeAttr", kFloat2_GrVertexAttribType, |
| SkSLType::kFloat2); |
| } |
| if (fPatchAttribs & PatchAttribs::kColor) { |
| fAttribs.emplace_back("dynamicColorAttr", |
| (fPatchAttribs & PatchAttribs::kWideColorIfEnabled) |
| ? kFloat4_GrVertexAttribType |
| : kUByte4_norm_GrVertexAttribType, |
| SkSLType::kHalf4); |
| } |
| if (fPatchAttribs & PatchAttribs::kExplicitCurveType) { |
| // A conic curve is written out with p3=[w,Infinity], but GPUs that don't support |
| // infinity can't detect this. On these platforms we write out an extra float with each |
| // patch that explicitly tells the shader what type of curve it is. |
| fAttribs.emplace_back("curveTypeAttr", kFloat_GrVertexAttribType, SkSLType::kFloat); |
| } |
| |
| this->setInstanceAttributesWithImplicitOffsets(fAttribs.data(), fAttribs.count()); |
| SkASSERT(this->instanceStride() == sizeof(SkPoint) * 4 + PatchAttribsStride(fPatchAttribs)); |
| if (!shaderCaps.vertexIDSupport()) { |
| constexpr static Attribute kVertexAttrib("edgeID", kFloat_GrVertexAttribType, |
| SkSLType::kFloat); |
| this->setVertexAttributesWithImplicitOffsets(&kVertexAttrib, 1); |
| } |
| SkASSERT(fAttribs.count() <= kMaxAttribCount); |
| } |
| |
| // This base class emits shader code for our parametric/radial stroke tessellation algorithm |
| // described above. The subclass emits its own specific setup code before calling into |
| // emitTessellationCode and emitFragment code. |
| class GrStrokeTessellationShader::Impl : public ProgramImpl { |
| void onEmitCode(EmitArgs&, GrGPArgs*) override; |
| |
| // Emits code that calculates the vertex position and any other inputs to the fragment shader. |
| // The onEmitCode() is responsible to define the following symbols before calling this method: |
| // |
| // // Functions. |
| // float2 unchecked_mix(float2, float2, float); |
| // float unchecked_mix(float, float, float); |
| // |
| // // Values provided by either uniforms or attribs. |
| // float2 p0, p1, p2, p3; |
| // float w; |
| // float STROKE_RADIUS; |
| // float 2x2 AFFINE_MATRIX; |
| // float2 TRANSLATE; |
| // |
| // // Values calculated by the specific subclass. |
| // float combinedEdgeID; |
| // bool isFinalEdge; |
| // float numParametricSegments; |
| // float radsPerSegment; |
| // float2 tan0; // Must be pre-normalized |
| // float2 tan1; // Must be pre-normalized |
| // float strokeOutset; |
| // |
| void emitTessellationCode(const GrStrokeTessellationShader& shader, SkString* code, |
| GrGPArgs* gpArgs, const GrShaderCaps& shaderCaps) const; |
| |
| // Emits all necessary fragment code. If using dynamic color, the impl is responsible to set up |
| // a half4 varying for color and provide its name in 'fDynamicColorName'. |
| void emitFragmentCode(const GrStrokeTessellationShader&, const EmitArgs&); |
| |
| void setData(const GrGLSLProgramDataManager& pdman, const GrShaderCaps&, |
| const GrGeometryProcessor&) final; |
| |
| GrGLSLUniformHandler::UniformHandle fTessControlArgsUniform; |
| GrGLSLUniformHandler::UniformHandle fTranslateUniform; |
| GrGLSLUniformHandler::UniformHandle fAffineMatrixUniform; |
| GrGLSLUniformHandler::UniformHandle fColorUniform; |
| SkString fDynamicColorName; |
| }; |
| |
| void GrStrokeTessellationShader::Impl::onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) { |
| 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->vertexIDSupport() ? 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(R"( |
| 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(R"( |
| 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);\n", affineMatrixName); |
| args.fVertBuilder->codeAppendf("float2 TRANSLATE = %s;\n", translateName); |
| |
| if (shader.hasExplicitCurveType()) { |
| args.fVertBuilder->insertFunction(SkStringPrintf(R"( |
| bool is_conic_curve() { return curveTypeAttr != %g; })", |
| skgpu::tess::kCubicCurveType).c_str()); |
| } else { |
| args.fVertBuilder->insertFunction(R"( |
| bool is_conic_curve() { return isinf(pts23Attr.w); })"); |
| } |
| |
| // Tessellation code. |
| args.fVertBuilder->codeAppend(R"( |
| 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(R"( |
| // 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(R"( |
| p0 = AFFINE_MATRIX * p0; |
| p1 = AFFINE_MATRIX * p1; |
| p2 = AFFINE_MATRIX * p2; |
| p3 = AFFINE_MATRIX * p3; |
| lastControlPoint = AFFINE_MATRIX * lastControlPoint;)"); |
| } |
| |
| args.fVertBuilder->codeAppend(R"( |
| // 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->vertexIDSupport()) { |
| // If we don't have sk_VertexID support then "edgeID" already came in as a vertex attrib. |
| args.fVertBuilder->codeAppend(R"( |
| 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(R"( |
| // 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(R"( |
| 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(R"( |
| float numEdgesInJoin = %i;)", |
| skgpu::tess::NumFixedEdgesInJoin(joinType)); |
| } |
| |
| args.fVertBuilder->codeAppend(R"( |
| // 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(R"( |
| // 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); |
| } |
| |
| void GrStrokeTessellationShader::Impl::emitTessellationCode( |
| const GrStrokeTessellationShader& shader, SkString* code, GrGPArgs* gpArgs, |
| const GrShaderCaps& shaderCaps) const { |
| // The subclass is responsible to define the following symbols before calling this method: |
| // |
| // // Functions. |
| // float2 unchecked_mix(float2, float2, float); |
| // float unchecked_mix(float, float, float); |
| // |
| // // Values provided by either uniforms or attribs. |
| // float2 p0, p1, p2, p3; |
| // float w; |
| // float STROKE_RADIUS; |
| // float 2x2 AFFINE_MATRIX; |
| // float2 TRANSLATE; |
| // |
| // // Values calculated by the specific subclass. |
| // float combinedEdgeID; |
| // bool isFinalEdge; |
| // float numParametricSegments; |
| // float radsPerSegment; |
| // float2 tan0; // Must be pre-normalized |
| // float2 tan1; // Must be pre-normalized |
| // float strokeOutset; |
| // |
| code->appendf(R"( |
| float2 tangent, strokeCoord; |
| if (combinedEdgeID != 0 && !isFinalEdge) { |
| // Compute the location and tangent direction of the stroke edge with the integral id |
| // "combinedEdgeID", where combinedEdgeID is the sorted-order index of parametric and radial |
| // edges. Start by finding the tangent function's power basis coefficients. These define a |
| // tangent direction (scaled by some uniform value) as: |
| // |T^2| |
| // Tangent_Direction(T) = dx,dy = |A 2B C| * |T | |
| // |. . .| |1 | |
| float2 A, B, C = p1 - p0; |
| float2 D = p3 - p0; |
| if (w >= 0.0) { |
| // P0..P2 represent a conic and P3==P2. The derivative of a conic has a cumbersome |
| // order-4 denominator. However, this isn't necessary if we are only interested in a |
| // vector in the same *direction* as a given tangent line. Since the denominator scales |
| // dx and dy uniformly, we can throw it out completely after evaluating the derivative |
| // with the standard quotient rule. This leaves us with a simpler quadratic function |
| // that we use to find a tangent. |
| C *= w; |
| B = .5*D - C; |
| A = (w - 1.0) * D; |
| p1 *= w; |
| } else { |
| float2 E = p2 - p1; |
| B = E - C; |
| A = fma(float2(-3), E, D); |
| } |
| // FIXME(crbug.com/800804,skbug.com/11268): Consider normalizing the exponents in A,B,C at |
| // this point in order to prevent fp32 overflow. |
| |
| // Now find the coefficients that give a tangent direction from a parametric edge ID: |
| // |
| // |parametricEdgeID^2| |
| // Tangent_Direction(parametricEdgeID) = dx,dy = |A B_ C_| * |parametricEdgeID | |
| // |. . .| |1 | |
| // |
| float2 B_ = B * (numParametricSegments * 2.0); |
| float2 C_ = C * (numParametricSegments * numParametricSegments); |
| |
| // Run a binary search to determine the highest parametric edge that is located on or before |
| // the combinedEdgeID. A combined ID is determined by the sum of complete parametric and |
| // radial segments behind it. i.e., find the highest parametric edge where: |
| // |
| // parametricEdgeID + floor(numRadialSegmentsAtParametricT) <= combinedEdgeID |
| // |
| float lastParametricEdgeID = 0.0; |
| float maxParametricEdgeID = min(numParametricSegments - 1.0, combinedEdgeID); |
| float negAbsRadsPerSegment = -abs(radsPerSegment); |
| float maxRotation0 = (1.0 + combinedEdgeID) * abs(radsPerSegment); |
| for (int exp = %i - 1; exp >= 0; --exp) { |
| // Test the parametric edge at lastParametricEdgeID + 2^exp. |
| float testParametricID = lastParametricEdgeID + exp2(float(exp)); |
| if (testParametricID <= maxParametricEdgeID) { |
| float2 testTan = fma(float2(testParametricID), A, B_); |
| testTan = fma(float2(testParametricID), testTan, C_); |
| float cosRotation = dot(normalize(testTan), tan0); |
| float maxRotation = fma(testParametricID, negAbsRadsPerSegment, maxRotation0); |
| maxRotation = min(maxRotation, PI); |
| // Is rotation <= maxRotation? (i.e., is the number of complete radial segments |
| // behind testT, + testParametricID <= combinedEdgeID?) |
| if (cosRotation >= cos(maxRotation)) { |
| // testParametricID is on or before the combinedEdgeID. Keep it! |
| lastParametricEdgeID = testParametricID; |
| } |
| } |
| } |
| |
| // Find the T value of the parametric edge at lastParametricEdgeID. |
| float parametricT = lastParametricEdgeID / numParametricSegments; |
| |
| // Now that we've identified the highest parametric edge on or before the |
| // combinedEdgeID, the highest radial edge is easy: |
| float lastRadialEdgeID = combinedEdgeID - lastParametricEdgeID; |
| |
| // Find the angle of tan0, i.e. the angle between tan0 and the positive x axis. |
| float angle0 = acos(clamp(tan0.x, -1.0, 1.0)); |
| angle0 = tan0.y >= 0.0 ? angle0 : -angle0; |
| |
| // Find the tangent vector on the edge at lastRadialEdgeID. By construction it is already |
| // normalized. |
| float radialAngle = fma(lastRadialEdgeID, radsPerSegment, angle0); |
| tangent = float2(cos(radialAngle), sin(radialAngle)); |
| float2 norm = float2(-tangent.y, tangent.x); |
| |
| // Find the T value where the tangent is orthogonal to norm. This is a quadratic: |
| // |
| // dot(norm, Tangent_Direction(T)) == 0 |
| // |
| // |T^2| |
| // norm * |A 2B C| * |T | == 0 |
| // |. . .| |1 | |
| // |
| float a=dot(norm,A), b_over_2=dot(norm,B), c=dot(norm,C); |
| float discr_over_4 = max(b_over_2*b_over_2 - a*c, 0.0); |
| float q = sqrt(discr_over_4); |
| if (b_over_2 > 0.0) { |
| q = -q; |
| } |
| q -= b_over_2; |
| |
| // Roots are q/a and c/q. Since each curve section does not inflect or rotate more than 180 |
| // degrees, there can only be one tangent orthogonal to "norm" inside 0..1. Pick the root |
| // nearest .5. |
| float _5qa = -.5*q*a; |
| float2 root = (abs(fma(q,q,_5qa)) < abs(fma(a,c,_5qa))) ? float2(q,a) : float2(c,q); |
| float radialT = (root.t != 0.0) ? root.s / root.t : 0.0; |
| radialT = clamp(radialT, 0.0, 1.0); |
| |
| if (lastRadialEdgeID == 0.0) { |
| // The root finder above can become unstable when lastRadialEdgeID == 0 (e.g., if |
| // there are roots at exatly 0 and 1 both). radialT should always == 0 in this case. |
| radialT = 0.0; |
| } |
| |
| // Now that we've identified the T values of the last parametric and radial edges, our final |
| // T value for combinedEdgeID is whichever is larger. |
| float T = max(parametricT, radialT); |
| |
| // Evaluate the cubic at T. Use De Casteljau's for its accuracy and stability. |
| float2 ab = unchecked_mix(p0, p1, T); |
| float2 bc = unchecked_mix(p1, p2, T); |
| float2 cd = unchecked_mix(p2, p3, T); |
| float2 abc = unchecked_mix(ab, bc, T); |
| float2 bcd = unchecked_mix(bc, cd, T); |
| float2 abcd = unchecked_mix(abc, bcd, T); |
| |
| // Evaluate the conic weight at T. |
| float u = unchecked_mix(1.0, w, T); |
| float v = w + 1 - u; // == mix(w, 1, T) |
| float uv = unchecked_mix(u, v, T); |
| |
| // If we went with T=parametricT, then update the tangent. Otherwise leave it at the radial |
| // tangent found previously. (In the event that parametricT == radialT, we keep the radial |
| // tangent.) |
| if (T != radialT) { |
| // We must re-normalize here because the tangent is determined by the curve coefficients |
| tangent = w >= 0.0 ? robust_normalize_diff(bc*u, ab*v) |
| : robust_normalize_diff(bcd, abc); |
| } |
| |
| strokeCoord = (w >= 0.0) ? abc/uv : abcd; |
| } else { |
| // Edges at the beginning and end of the strip use exact endpoints and tangents. This |
| // ensures crack-free seaming between instances. |
| tangent = (combinedEdgeID == 0) ? tan0 : tan1; |
| strokeCoord = (combinedEdgeID == 0) ? p0 : p3; |
| })", skgpu::tess::kMaxResolveLevel /* Parametric/radial sort loop count. */); |
| |
| code->append(R"( |
| // At this point 'tangent' is normalized, so the orthogonal vector is also normalized. |
| float2 ortho = float2(tangent.y, -tangent.x); |
| strokeCoord += ortho * (STROKE_RADIUS * strokeOutset);)"); |
| |
| if (!shader.stroke().isHairlineStyle()) { |
| // Normal case. Do the transform after tessellation. |
| code->append(R"( |
| float2 devCoord = AFFINE_MATRIX * strokeCoord + TRANSLATE;)"); |
| gpArgs->fPositionVar.set(SkSLType::kFloat2, "devCoord"); |
| gpArgs->fLocalCoordVar.set(SkSLType::kFloat2, "strokeCoord"); |
| } else { |
| // Hairline case. The scale and skew already happened before tessellation. |
| code->append(R"( |
| float2 devCoord = strokeCoord + TRANSLATE; |
| float2 localCoord = inverse(AFFINE_MATRIX) * strokeCoord;)"); |
| gpArgs->fPositionVar.set(SkSLType::kFloat2, "devCoord"); |
| gpArgs->fLocalCoordVar.set(SkSLType::kFloat2, "localCoord"); |
| } |
| } |
| |
| void GrStrokeTessellationShader::Impl::emitFragmentCode(const GrStrokeTessellationShader& shader, |
| const EmitArgs& args) { |
| if (!shader.hasDynamicColor()) { |
| // The fragment shader just outputs a uniform color. |
| const char* colorUniformName; |
| fColorUniform = args.fUniformHandler->addUniform(nullptr, kFragment_GrShaderFlag, |
| SkSLType::kHalf4, "color", |
| &colorUniformName); |
| args.fFragBuilder->codeAppendf("half4 %s = %s;", args.fOutputColor, colorUniformName); |
| } else { |
| args.fFragBuilder->codeAppendf("half4 %s = %s;", args.fOutputColor, |
| fDynamicColorName.c_str()); |
| } |
| args.fFragBuilder->codeAppendf("const half4 %s = half4(1);", args.fOutputCoverage); |
| } |
| |
| void GrStrokeTessellationShader::Impl::setData(const GrGLSLProgramDataManager& pdman, |
| const GrShaderCaps&, |
| const GrGeometryProcessor& geomProc) { |
| 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()); |
| } |
| } |
| |
| void GrStrokeTessellationShader::addToKey(const GrShaderCaps&, skgpu::KeyBuilder* b) const { |
| bool keyNeedsJoin = !(fPatchAttribs & PatchAttribs::kStrokeParams); |
| SkASSERT(fStroke.getJoin() >> 2 == 0); |
| // Attribs get worked into the key automatically during GrGeometryProcessor::getAttributeKey(). |
| // When color is in a uniform, it's always wide. kWideColor doesn't need to be considered here. |
| uint32_t key = (uint32_t)(fPatchAttribs & ~PatchAttribs::kColor); |
| key = (key << 2) | ((keyNeedsJoin) ? fStroke.getJoin() : 0); |
| key = (key << 1) | (uint32_t)fStroke.isHairlineStyle(); |
| b->add32(key); |
| } |
| |
| std::unique_ptr<GrGeometryProcessor::ProgramImpl> GrStrokeTessellationShader::makeProgramImpl( |
| const GrShaderCaps&) const { |
| return std::make_unique<Impl>(); |
| } |