1 | /* |
2 | * Copyright 2020 Google LLC. |
3 | * |
4 | * Use of this source code is governed by a BSD-style license that can be |
5 | * found in the LICENSE file. |
6 | */ |
7 | |
8 | #ifndef GrStrokeTessellateShader_DEFINED |
9 | #define GrStrokeTessellateShader_DEFINED |
10 | |
11 | #include "src/gpu/tessellate/GrPathShader.h" |
12 | |
13 | #include "src/gpu/tessellate/GrTessellationPathRenderer.h" |
14 | |
15 | class GrGLSLUniformHandler; |
16 | |
17 | // Tessellates a batch of stroke patches directly to the canvas. A patch is either a "cubic" |
18 | // (single stroked bezier curve with butt caps) or a "join". A patch is defined by 5 points as |
19 | // follows: |
20 | // |
21 | // P0..P3 : Represent the cubic control points. |
22 | // (P4.x == 0) : The patch is a cubic and the shader decides how many linear segments to produce. |
23 | // (P4.x < 0) : The patch is still a cubic, but will be linearized into exactly |P4.x| segments. |
24 | // (P4.x == 1) : The patch is an outer bevel join. |
25 | // (P4.x == 2) : The patch is an outer miter join. |
26 | // (NOTE: If miterLimitOrZero == 0, then miter join patches are illegal.) |
27 | // (P4.x == 3) : The patch is an outer round join. |
28 | // (P4.x == 4) : The patch is an inner and outer round join. |
29 | // P4.y : Represents the stroke radius. |
30 | // |
31 | // If a patch is a join, P0 must equal P3, P1 must equal the control point coming into the junction, |
32 | // and P2 must equal the control point going out. It's imperative that a junction's control points |
33 | // match the control points of their neighbor cubics exactly, or the rasterization might not be |
34 | // water tight. (Also note that if P1==P0 or P2==P3, the junction needs to be given its neighbor's |
35 | // opposite cubic control point.) |
36 | // |
37 | // To use this shader, construct a GrProgramInfo with a primitiveType of "kPatches" and a |
38 | // tessellationPatchVertexCount of 5. |
39 | class GrStrokeTessellateShader : public GrPathShader { |
40 | public: |
41 | constexpr static float kBevelJoinType = -1; |
42 | constexpr static float kMiterJoinType = -2; |
43 | constexpr static float kRoundJoinType = -3; |
44 | constexpr static float kInternalRoundJoinType = -4; |
45 | |
46 | constexpr static int kNumVerticesPerPatch = 5; |
47 | |
48 | // 'skewMatrix' is applied to the post-tessellation triangles. It cannot expand the geometry in |
49 | // any direction. For now, patches should be pre-scaled on CPU by the view matrix's maxScale, |
50 | // which leaves 'skewMatrix' as the original view matrix divided by maxScale. |
51 | // |
52 | // If 'miterLimitOrZero' is zero, then the patches being drawn cannot include any miter joins. |
53 | // If a stroke uses miter joins with a miter limit of zero, then they need to be pre-converted |
54 | // to bevel joins. |
55 | GrStrokeTessellateShader(const SkMatrix& skewMatrix, SkPMColor4f color, float miterLimitOrZero) |
56 | : GrPathShader(kTessellate_GrStrokeTessellateShader_ClassID, skewMatrix, |
57 | GrPrimitiveType::kPatches, kNumVerticesPerPatch) |
58 | , fColor(color) |
59 | , fMiterLimitOrZero(miterLimitOrZero) { |
60 | // Since the skewMatrix is applied after tessellation, it cannot expand the geometry in any |
61 | // direction. (The caller can create a skewMatrix by dividing their viewMatrix by its |
62 | // maxScale and then pre-multiplying their control points by the same maxScale.) |
63 | SkASSERT(skewMatrix.getMaxScale() < 1 + SK_ScalarNearlyZero); |
64 | constexpr static Attribute kInputPointAttrib{"inputPoint" , kFloat2_GrVertexAttribType, |
65 | kFloat2_GrSLType}; |
66 | this->setVertexAttributes(&kInputPointAttrib, 1); |
67 | } |
68 | |
69 | private: |
70 | const char* name() const override { return "GrStrokeTessellateShader" ; } |
71 | void getGLSLProcessorKey(const GrShaderCaps&, GrProcessorKeyBuilder* b) const override { |
72 | b->add32(this->viewMatrix().isIdentity()); |
73 | } |
74 | GrGLSLPrimitiveProcessor* createGLSLInstance(const GrShaderCaps&) const final; |
75 | |
76 | SkString getTessControlShaderGLSL(const GrGLSLPrimitiveProcessor*, |
77 | const char* versionAndExtensionDecls, |
78 | const GrGLSLUniformHandler&, |
79 | const GrShaderCaps&) const override; |
80 | SkString getTessEvaluationShaderGLSL(const GrGLSLPrimitiveProcessor*, |
81 | const char* versionAndExtensionDecls, |
82 | const GrGLSLUniformHandler&, |
83 | const GrShaderCaps&) const override; |
84 | |
85 | const SkPMColor4f fColor; |
86 | const float fMiterLimitOrZero; // Zero if there will not be any miter join patches. |
87 | |
88 | class Impl; |
89 | }; |
90 | |
91 | #endif |
92 | |