1 /* 2 * Copyright 2017 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 SkOffsetPolygon_DEFINED 9 #define SkOffsetPolygon_DEFINED 10 11 #include <functional> 12 13 #include "include/core/SkPoint.h" 14 #include "include/private/SkTDArray.h" 15 16 struct SkRect; 17 18 /** 19 * Generates a polygon that is inset a constant from the boundary of a given convex polygon. 20 * 21 * @param inputPolygonVerts Array of points representing the vertices of the original polygon. 22 * It should be convex and have no coincident points. 23 * @param inputPolygonSize Number of vertices in the original polygon. 24 * @param inset How far we wish to inset the polygon. This should be a positive value. 25 * @param insetPolygon The resulting inset polygon, if any. 26 * @return true if an inset polygon exists, false otherwise. 27 */ 28 bool SkInsetConvexPolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize, 29 SkScalar inset, SkTDArray<SkPoint>* insetPolygon); 30 31 /** 32 * Generates a simple polygon (if possible) that is offset a constant distance from the boundary 33 * of a given simple polygon. 34 * The input polygon must be simple and have no coincident vertices or collinear edges. 35 * 36 * @param inputPolygonVerts Array of points representing the vertices of the original polygon. 37 * @param inputPolygonSize Number of vertices in the original polygon. 38 * @param bounds Bounding rectangle for the original polygon. 39 * @param offset How far we wish to offset the polygon. 40 * Positive values indicate insetting, negative values outsetting. 41 * @param offsetPolgon The resulting offset polygon, if any. 42 * @param polygonIndices The indices of the original polygon that map to the new one. 43 * @return true if an offset simple polygon exists, false otherwise. 44 */ 45 bool SkOffsetSimplePolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize, 46 const SkRect& bounds, SkScalar offset, SkTDArray<SkPoint>* offsetPolygon, 47 SkTDArray<int>* polygonIndices = nullptr); 48 49 /** 50 * Compute the number of points needed for a circular join when offsetting a vertex. 51 * The lengths of offset0 and offset1 don't have to equal |offset| -- only the direction matters. 52 * The segment lengths will be approximately four pixels. 53 * 54 * @param offset0 Starting offset vector direction. 55 * @param offset1 Ending offset vector direction. 56 * @param offset Offset value (can be negative). 57 * @param rotSin Sine of rotation delta per step. 58 * @param rotCos Cosine of rotation delta per step. 59 * @param n Number of steps to fill out the arc. 60 * @return true for success, false otherwise 61 */ 62 bool SkComputeRadialSteps(const SkVector& offset0, const SkVector& offset1, SkScalar offset, 63 SkScalar* rotSin, SkScalar* rotCos, int* n); 64 65 /** 66 * Determine winding direction for a polygon. 67 * The input polygon must be simple or the result will be meaningless. 68 * 69 * @param polygonVerts Array of points representing the vertices of the polygon. 70 * @param polygonSize Number of vertices in the polygon. 71 * @return 1 for cw, -1 for ccw, and 0 if zero signed area (either degenerate or self-intersecting). 72 * The y-axis is assumed to be pointing down. 73 */ 74 int SkGetPolygonWinding(const SkPoint* polygonVerts, int polygonSize); 75 76 /** 77 * Determine whether a polygon is convex or not. 78 * 79 * @param polygonVerts Array of points representing the vertices of the polygon. 80 * @param polygonSize Number of vertices in the polygon. 81 * @return true if the polygon is convex, false otherwise. 82 */ 83 bool SkIsConvexPolygon(const SkPoint* polygonVerts, int polygonSize); 84 85 /** 86 * Determine whether a polygon is simple (i.e., not self-intersecting) or not. 87 * The input polygon must have no coincident vertices or the test will fail. 88 * 89 * @param polygonVerts Array of points representing the vertices of the polygon. 90 * @param polygonSize Number of vertices in the polygon. 91 * @return true if the polygon is simple, false otherwise. 92 */ 93 bool SkIsSimplePolygon(const SkPoint* polygonVerts, int polygonSize); 94 95 /** 96 * Compute indices to triangulate the given polygon. 97 * The input polygon must be simple (i.e. it is not self-intersecting) 98 * and have no coincident vertices or collinear edges. 99 * 100 * @param polygonVerts Array of points representing the vertices of the polygon. 101 * @param indexMap Mapping from index in the given array to the final index in the triangulation. 102 * @param polygonSize Number of vertices in the polygon. 103 * @param triangleIndices Indices of the resulting triangulation. 104 * @return true if successful, false otherwise. 105 */ 106 bool SkTriangulateSimplePolygon(const SkPoint* polygonVerts, uint16_t* indexMap, int polygonSize, 107 SkTDArray<uint16_t>* triangleIndices); 108 109 // Experiment: doesn't handle really big floats (returns false), always returns true for count <= 3 110 bool SkIsPolyConvex_experimental(const SkPoint[], int count); 111 112 #endif 113