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