forked from mirror/DotRecast
86 lines
2.9 KiB
C#
86 lines
2.9 KiB
C#
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/*
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recast4j copyright (c) 2021 Piotr Piastucki piotr@jtilia.org
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This software is provided 'as-is', without any express or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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1. The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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2. Altered source versions must be plainly marked as such, and must not be
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misrepresented as being the original software.
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3. This notice may not be removed or altered from any source distribution.
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*/
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using System.Collections.Generic;
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namespace DotRecast.Core;
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public static class ConvexUtils {
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// Calculates convex hull on xz-plane of points on 'pts',
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// stores the indices of the resulting hull in 'out' and
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// returns number of points on hull.
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public static List<int> convexhull(List<float> pts) {
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int npts = pts.Count / 3;
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List<int> @out = new();
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// Find lower-leftmost point.
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int hull = 0;
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for (int i = 1; i < npts; ++i) {
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float[] a = new float[] { pts[i * 3], pts[i * 3 + 1], pts[i * 3 + 2] };
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float[] b = new float[] { pts[hull * 3], pts[hull * 3 + 1], pts[hull * 3 + 2] };
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if (cmppt(a, b)) {
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hull = i;
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}
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}
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// Gift wrap hull.
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int endpt = 0;
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do {
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@out.Add(hull);
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endpt = 0;
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for (int j = 1; j < npts; ++j) {
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float[] a = new float[] { pts[hull * 3], pts[hull * 3 + 1], pts[hull * 3 + 2] };
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float[] b = new float[] { pts[endpt * 3], pts[endpt * 3 + 1], pts[endpt * 3 + 2] };
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float[] c = new float[] { pts[j * 3], pts[j * 3 + 1], pts[j * 3 + 2] };
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if (hull == endpt || left(a, b, c)) {
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endpt = j;
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}
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}
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hull = endpt;
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} while (endpt != @out[0]);
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return @out;
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}
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// Returns true if 'a' is more lower-left than 'b'.
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private static bool cmppt(float[] a, float[] b) {
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if (a[0] < b[0]) {
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return true;
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}
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if (a[0] > b[0]) {
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return false;
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}
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if (a[2] < b[2]) {
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return true;
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}
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if (a[2] > b[2]) {
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return false;
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}
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return false;
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}
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// Returns true if 'c' is left of line 'a'-'b'.
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private static bool left(float[] a, float[] b, float[] c) {
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float u1 = b[0] - a[0];
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float v1 = b[2] - a[2];
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float u2 = c[0] - a[0];
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float v2 = c[2] - a[2];
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return u1 * v2 - v1 * u2 < 0;
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}
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}
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