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/*
* 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 =
"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 =
"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 =
"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 =
"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 =
"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.fInfinitySupport != (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.size());
SkASSERT(this->instanceStride() == sizeof(SkPoint) * 4 + PatchAttribsStride(fPatchAttribs));
if (!shaderCaps.fVertexIDSupport) {
constexpr static Attribute kVertexAttrib("edgeID", kFloat_GrVertexAttribType,
SkSLType::kFloat);
this->setVertexAttributesWithImplicitOffsets(&kVertexAttrib, 1);
}
SkASSERT(fAttribs.size() <= 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->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);
}
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(
"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(
// 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("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(
"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>();
}