mirror of https://github.com/ArduPilot/ardupilot
79 lines
2.9 KiB
C++
79 lines
2.9 KiB
C++
/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
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/*
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* polygon.cpp
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* Copyright (C) Andrew Tridgell 2011
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*
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* This file is free software: you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This file is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "AP_Math.h"
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/*
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NOTE: the winding number crossing algorithm is based on
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the code from
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http://www.softsurfer.com/Archive/algorithm_0103/algorithm_0103.htm
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which has the following copyright notice:
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// Copyright 2001, softSurfer (www.softsurfer.com)
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// This code may be freely used and modified for any purpose
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// providing that this copyright notice is included with it.
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// SoftSurfer makes no warranty for this code, and cannot be held
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// liable for any real or imagined damage resulting from its use.
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// Users of this code must verify correctness for their application.
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*/
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/* isLeft(): tests if a point is Left|On|Right of an infinite line.
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Input: three points P0, P1, and P2
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Return: >0 for P2 left of the line through P0 and P1
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=0 for P2 on the line
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<0 for P2 right of the line
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See: the January 2001 Algorithm "Area of 2D and 3D Triangles and Polygons"
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*/
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static int isLeft(const Vector2f *P0, const Vector2f *P1, const Vector2f *P2)
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{
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float ret = ( (P1->x - P0->x) * (P2->y - P0->y)
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- (P2->x - P0->x) * (P1->y - P0->y) );
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if (ret > 0) return 1;
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if (ret < 0) return -1;
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return 0;
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}
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/*
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Polygon_outside(): winding number test for a point in a polygon
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Input: P = a point,
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V[] = vertex points of a polygon V[n+1] with V[n]=V[0]
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Return: true if P is outside the polygon
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*/
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bool Polygon_outside(const Vector2f *P, const Vector2f *V, unsigned n)
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{
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int wn = 0; // the winding number counter
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// loop through all edges of the polygon
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for (unsigned i=0; i<n; i++) { // edge from V[i] to V[i+1]
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if (V[i].y <= P->y) { // start y <= P.y
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if (V[i+1].y > P->y) // an upward crossing
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if (isLeft(&V[i], &V[i+1], P) > 0) // P left of edge
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++wn; // have a valid up intersect
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}
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else { // start y > P.y (no test needed)
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if (V[i+1].y <= P->y) // a downward crossing
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if (isLeft(&V[i], &V[i+1], P) < 0) // P right of edge
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--wn; // have a valid down intersect
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}
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}
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return wn == 0;
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}
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