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/*
* Copyright 2019 Google LLC.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef GrPathTessellationShader_DEFINED
#define GrPathTessellationShader_DEFINED
#include "src/gpu/tessellate/shaders/GrTessellationShader.h"
// This is the base class for shaders in the GPU tessellator that fill paths.
class GrPathTessellationShader : public GrTessellationShader {
public:
// Draws a simple array of triangles.
static GrPathTessellationShader* MakeSimpleTriangleShader(SkArenaAlloc*,
const SkMatrix& viewMatrix,
const SkPMColor4f&);
// How many triangles are in a curve with 2^resolveLevel line segments?
constexpr static int NumCurveTrianglesAtResolveLevel(int resolveLevel) {
// resolveLevel=0 -> 0 line segments -> 0 triangles
// resolveLevel=1 -> 2 line segments -> 1 triangle
// resolveLevel=2 -> 4 line segments -> 3 triangles
// resolveLevel=3 -> 8 line segments -> 7 triangles
// ...
return (1 << resolveLevel) - 1;
}
enum class PatchType : bool {
// An ice cream cone shaped patch, with 4 curve control points on top of a triangle that
// fans from a 5th point at the center of the contour. (5 points per patch.)
kWedges,
// A standalone closed curve made up 4 control points. (4 points per patch.)
kCurves
};
// Uses instanced draws to triangulate curves with a "middle-out" topology. Middle-out draws a
// triangle with vertices at T=[0, 1/2, 1] and then recurses breadth first:
//
// depth=0: T=[0, 1/2, 1]
// depth=1: T=[0, 1/4, 2/4], T=[2/4, 3/4, 1]
// depth=2: T=[0, 1/8, 2/8], T=[2/8, 3/8, 4/8], T=[4/8, 5/8, 6/8], T=[6/8, 7/8, 1]
// ...
//
// The shader determines how many segments are required to render each individual curve
// smoothly, and emits empty triangles at any vertices whose sk_VertexIDs are higher than
// necessary. It is the caller's responsibility to draw enough vertices per instance for the
// most complex curve in the batch to render smoothly (i.e., NumTrianglesAtResolveLevel() * 3).
static GrPathTessellationShader* MakeMiddleOutFixedCountShader(const GrShaderCaps&,
SkArenaAlloc*,
const SkMatrix& viewMatrix,
const SkPMColor4f&, PatchType);
// This is the largest number of segments the middle-out shader will accept in a single
// instance. If a curve requires more segments, it needs to be chopped.
constexpr static int kMaxFixedCountSegments = 32;
constexpr static int kMaxFixedCountResolveLevel = 5; // log2(kMaxFixedCountSegments)
static_assert(kMaxFixedCountSegments == 1 << kMaxFixedCountResolveLevel);
// These functions define the vertex and index buffers that should be bound when drawing with
// the middle-out fixed count shader. The data sequence is identical for any length of
// tessellation segments, so the caller can use them with any instance length (up to
// kMaxFixedCountResolveLevel).
//
// The "curve" and "wedge" buffers are nearly identical, but we keep them separate for now in
// case there is a perf hit in the curve case for not using index 0.
constexpr static int SizeOfVertexBufferForMiddleOutCurves() {
constexpr int kMaxVertexCount = (1 << kMaxFixedCountResolveLevel) + 1;
return kMaxVertexCount * kMiddleOutVertexStride;
}
static void InitializeVertexBufferForMiddleOutCurves(GrVertexWriter, size_t bufferSize);
constexpr static size_t SizeOfIndexBufferForMiddleOutCurves() {
constexpr int kMaxTriangleCount =
NumCurveTrianglesAtResolveLevel(kMaxFixedCountResolveLevel);
return kMaxTriangleCount * 3 * sizeof(uint16_t);
}
static void InitializeIndexBufferForMiddleOutCurves(GrVertexWriter, size_t bufferSize);
constexpr static int SizeOfVertexBufferForMiddleOutWedges() {
return SizeOfVertexBufferForMiddleOutCurves() + kMiddleOutVertexStride;
}
static void InitializeVertexBufferForMiddleOutWedges(GrVertexWriter, size_t bufferSize);
constexpr static size_t SizeOfIndexBufferForMiddleOutWedges() {
return SizeOfIndexBufferForMiddleOutCurves() + 3 * sizeof(uint16_t);
}
static void InitializeIndexBufferForMiddleOutWedges(GrVertexWriter, size_t bufferSize);
// Uses GPU tessellation shaders to linearize, triangulate, and render cubic "wedge" patches. A
// wedge is a 5-point patch consisting of 4 cubic control points, plus an anchor point fanning
// from the center of the curve's resident contour.
static GrPathTessellationShader* MakeHardwareTessellationShader(SkArenaAlloc*,
const SkMatrix& viewMatrix,
const SkPMColor4f&, PatchType);
// Returns the stencil settings to use for a standard Redbook "stencil" pass.
static const GrUserStencilSettings* StencilPathSettings(GrFillRule fillRule) {
// Increments clockwise triangles and decrements counterclockwise. Used for "winding" fill.
constexpr static GrUserStencilSettings kIncrDecrStencil(
GrUserStencilSettings::StaticInitSeparate<
0x0000, 0x0000,
GrUserStencilTest::kAlwaysIfInClip, GrUserStencilTest::kAlwaysIfInClip,
0xffff, 0xffff,
GrUserStencilOp::kIncWrap, GrUserStencilOp::kDecWrap,
GrUserStencilOp::kKeep, GrUserStencilOp::kKeep,
0xffff, 0xffff>());
// Inverts the bottom stencil bit. Used for "even/odd" fill.
constexpr static GrUserStencilSettings kInvertStencil(
GrUserStencilSettings::StaticInit<
0x0000,
GrUserStencilTest::kAlwaysIfInClip,
0xffff,
GrUserStencilOp::kInvert,
GrUserStencilOp::kKeep,
0x0001>());
return (fillRule == GrFillRule::kNonzero) ? &kIncrDecrStencil : &kInvertStencil;
}
// Returns the stencil settings to use for a standard Redbook "fill" pass. Allows non-zero
// stencil values to pass and write a color, and resets the stencil value back to zero; discards
// immediately on stencil values of zero.
static const GrUserStencilSettings* TestAndResetStencilSettings(bool isInverseFill = false) {
constexpr static GrUserStencilSettings kTestAndResetStencil(
GrUserStencilSettings::StaticInit<
0x0000,
// No need to check the clip because the previous stencil pass will have only
// written to samples already inside the clip.
GrUserStencilTest::kNotEqual,
0xffff,
GrUserStencilOp::kZero,
GrUserStencilOp::kKeep,
0xffff>());
constexpr static GrUserStencilSettings kTestAndResetStencilInverted(
GrUserStencilSettings::StaticInit<
0x0000,
// No need to check the clip because the previous stencil pass will have only
// written to samples already inside the clip.
GrUserStencilTest::kEqual,
0xffff,
GrUserStencilOp::kKeep,
GrUserStencilOp::kZero,
0xffff>());
return isInverseFill ? &kTestAndResetStencilInverted : &kTestAndResetStencil;
}
// Creates a pipeline that does not write to the color buffer.
static const GrPipeline* MakeStencilOnlyPipeline(
const ProgramArgs&,
GrAAType,
const GrAppliedHardClip&,
GrPipeline::InputFlags = GrPipeline::InputFlags::kNone);
protected:
constexpr static size_t kMiddleOutVertexStride = 2 * sizeof(float);
GrPathTessellationShader(ClassID classID, GrPrimitiveType primitiveType,
int tessellationPatchVertexCount, const SkMatrix& viewMatrix,
const SkPMColor4f& color)
: GrTessellationShader(classID, primitiveType, tessellationPatchVertexCount, viewMatrix,
color) {
}
// Default path tessellation shader implementation that manages a uniform matrix and color.
class Impl : public ProgramImpl {
public:
void onEmitCode(EmitArgs&, GrGPArgs*) final;
void setData(const GrGLSLProgramDataManager&, const GrShaderCaps&,
const GrGeometryProcessor&) override;
protected:
// float4x3 unpack_rational_cubic(float2 p0, float2 p1, float2 p2, float2 p3) { ...
//
// Evaluate our point of interest using numerically stable linear interpolations. We add our
// own "safe_mix" method to guarantee we get exactly "b" when T=1. The builtin mix()
// function seems spec'd to behave this way, but empirical results results have shown it
// does not always.
static const char* kEvalRationalCubicFn;
virtual void emitVertexCode(const GrShaderCaps&, const GrPathTessellationShader&,
GrGLSLVertexBuilder*, GrGPArgs*) = 0;
GrGLSLUniformHandler::UniformHandle fAffineMatrixUniform;
GrGLSLUniformHandler::UniformHandle fTranslateUniform;
GrGLSLUniformHandler::UniformHandle fColorUniform;
};
};
#endif