1 /* 2 * Copyright 2020 Google Inc. 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 GrAATriangulator_DEFINED 9 #define GrAATriangulator_DEFINED 10 11 #if !defined(SK_ENABLE_OPTIMIZE_SIZE) 12 13 #include "src/gpu/ganesh/geometry/GrTriangulator.h" 14 15 // Triangulates the given path in device space with a mesh of alpha ramps for antialiasing. 16 class GrAATriangulator : private GrTriangulator { 17 public: PathToAATriangles(const SkPath & path,SkScalar tolerance,const SkRect & clipBounds,GrEagerVertexAllocator * vertexAllocator)18 static int PathToAATriangles(const SkPath& path, SkScalar tolerance, const SkRect& clipBounds, 19 GrEagerVertexAllocator* vertexAllocator) { 20 SkArenaAlloc alloc(kArenaDefaultChunkSize); 21 GrAATriangulator aaTriangulator(path, &alloc); 22 aaTriangulator.fRoundVerticesToQuarterPixel = true; 23 aaTriangulator.fEmitCoverage = true; 24 bool isLinear; 25 auto [ polys, success ] = aaTriangulator.pathToPolys(tolerance, clipBounds, &isLinear); 26 if (!success) { 27 return 0; 28 } 29 return aaTriangulator.polysToAATriangles(polys, vertexAllocator); 30 } 31 32 // Structs used by GrAATriangulator internals. 33 struct SSEdge; 34 struct EventList; 35 struct Event { EventEvent36 Event(SSEdge* edge, const SkPoint& point, uint8_t alpha) 37 : fEdge(edge), fPoint(point), fAlpha(alpha) {} 38 SSEdge* fEdge; 39 SkPoint fPoint; 40 uint8_t fAlpha; 41 void apply(VertexList* mesh, const Comparator&, EventList* events, GrAATriangulator*); 42 }; 43 struct EventComparator { 44 enum class Op { kLessThan, kGreaterThan }; EventComparatorEventComparator45 EventComparator(Op op) : fOp(op) {} operatorEventComparator46 bool operator() (Event* const &e1, Event* const &e2) { 47 return fOp == Op::kLessThan ? e1->fAlpha < e2->fAlpha 48 : e1->fAlpha > e2->fAlpha; 49 } 50 Op fOp; 51 }; 52 53 private: GrAATriangulator(const SkPath & path,SkArenaAlloc * alloc)54 GrAATriangulator(const SkPath& path, SkArenaAlloc* alloc) : GrTriangulator(path, alloc) {} 55 56 // For screenspace antialiasing, the algorithm is modified as follows: 57 // 58 // Run steps 1-5 above to produce polygons. 59 // 5b) Apply fill rules to extract boundary contours from the polygons: 60 void extractBoundary(EdgeList* boundary, Edge* e) const; 61 void extractBoundaries(const VertexList& inMesh, VertexList* innerVertices, 62 const Comparator&); 63 64 // 5c) Simplify boundaries to remove "pointy" vertices that cause inversions: 65 void simplifyBoundary(EdgeList* boundary, const Comparator&); 66 67 // 5d) Displace edges by half a pixel inward and outward along their normals. Intersect to find 68 // new vertices, and set zero alpha on the exterior and one alpha on the interior. Build a 69 // new antialiased mesh from those vertices: 70 void strokeBoundary(EdgeList* boundary, VertexList* innerMesh, const Comparator&); 71 72 // Run steps 3-6 above on the new mesh, and produce antialiased triangles. 73 std::tuple<Poly*, bool> tessellate(const VertexList& mesh, const Comparator&) override; 74 int polysToAATriangles(Poly*, GrEagerVertexAllocator*) const; 75 76 // Additional helpers and driver functions. 77 void makeEvent(SSEdge*, EventList* events) const; 78 void makeEvent(SSEdge*, Vertex* v, SSEdge* other, Vertex* dest, EventList* events, 79 const Comparator&) const; 80 void connectPartners(VertexList* mesh, const Comparator&); 81 void removeNonBoundaryEdges(const VertexList& mesh) const; 82 void connectSSEdge(Vertex* v, Vertex* dest, const Comparator&); 83 bool collapseOverlapRegions(VertexList* mesh, const Comparator&, EventComparator comp); 84 85 // FIXME: fOuterMesh should be plumbed through function parameters instead. 86 mutable VertexList fOuterMesh; 87 }; 88 89 #endif // SK_ENABLE_OPTIMIZE_SIZE 90 91 #endif // GrAATriangulator_DEFINED 92