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
16struct 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 */
28bool 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 */
45bool 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 */
62bool 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 */
74int 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 */
83bool 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
110bool SkIsPolyConvex_experimental(const SkPoint[], int count);
111
112#endif
113