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196 lines
6.4 KiB
C++
196 lines
6.4 KiB
C++
/* ScummVM - Graphic Adventure Engine
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*
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* ScummVM is the legal property of its developers, whose names
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* are too numerous to list here. Please refer to the COPYRIGHT
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* file distributed with this source distribution.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* 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
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*
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*/
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/*
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* This code is based on Broken Sword 2.5 engine
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*
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* Copyright (c) Malte Thiesen, Daniel Queteschiner and Michael Elsdoerfer
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*
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* Licensed under GNU GPL v2
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*
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*/
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/*
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BS_Line
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-------
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This class contains only static methods, which have to do with straight line
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segments. There is no real straight line segment class. Calculations will be
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used with polygons, and it is important the process of starting and selecting
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endpoints of lines is dynamic. This would prhobit a polygon from a set
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being formed by fixed line segments
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Autor: Malte Thiesen
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*/
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#ifndef SWORD25_LINE_H
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#define SWORD25_LINE_H
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#include "sword25/kernel/common.h"
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namespace Sword25 {
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class Line {
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public:
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/**
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* Determines whether a piont is left of a line
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* @param a The start point of a line
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* @param b The end point of a line
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* @param c The test point
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* @return Returns true if the point is to the left of the line.
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* If the point is to the right of the line or on the line, false is returned.
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*/
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static bool isVertexLeft(const Vertex &a, const Vertex &b, const Vertex &c) {
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return triangleArea2(a, b, c) > 0;
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}
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static bool isVertexLeftOn(const Vertex &a, const Vertex &b, const Vertex &c) {
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return triangleArea2(a, b, c) >= 0;
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}
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/**
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* Determines whether a piont is right of a line
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* @param a The start point of a line
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* @param b The end point of a line
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* @param c The test point
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* @return Returns true if the point is to the right of the line.
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* If the point is to the right of the line or on the line, false is returned.
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*/
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static bool isVertexRight(const Vertex &a, const Vertex &b, const Vertex &c) {
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return triangleArea2(a, b, c) < 0;
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}
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static bool isVertexRightOn(const Vertex &a, const Vertex &b, const Vertex &c) {
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return triangleArea2(a, b, c) <= 0;
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}
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/**
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* Determines whether a piont is on a line
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* @param a The start point of a line
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* @param b The end point of a line
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* @param c The test point
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* @return Returns true if the point is on the line, false otherwise.
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*/
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static bool isVertexOn(const Vertex &a, const Vertex &b, const Vertex &c) {
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return triangleArea2(a, b, c) == 0;
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}
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enum VERTEX_CLASSIFICATION {
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LEFT,
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RIGHT,
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ON
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};
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/**
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* Determines where a point is relative to a line.
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* @param a The start point of a line
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* @param b The end point of a line
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* @param c The test point
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* @return LEFT is returned if the point is to the left of the line.
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* RIGHT is returned if the point is to the right of the line.
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* ON is returned if the point is on the line.
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*/
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static VERTEX_CLASSIFICATION classifyVertexToLine(const Vertex &a, const Vertex &b, const Vertex &c) {
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int area = triangleArea2(a, b, c);
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if (area > 0) return LEFT;
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if (area < 0) return RIGHT;
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return ON;
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}
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/**
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* Determines whether two lines intersect
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* @param a The start point of the first line
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* @param b The end point of the first line
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* @param c The start point of the second line
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* @param d The end point of the second line
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* @remark In cases where a line only touches the other, false is returned (improper intersection)
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*/
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static bool doesIntersectProperly(const Vertex &a, const Vertex &b, const Vertex &c, const Vertex &d) {
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VERTEX_CLASSIFICATION class1 = classifyVertexToLine(a, b, c);
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VERTEX_CLASSIFICATION class2 = classifyVertexToLine(a, b, d);
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VERTEX_CLASSIFICATION class3 = classifyVertexToLine(c, d, a);
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VERTEX_CLASSIFICATION class4 = classifyVertexToLine(c, d, b);
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if (class1 == ON || class2 == ON || class3 == ON || class4 == ON) return false;
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return ((class1 == LEFT) ^(class2 == LEFT)) && ((class3 == LEFT) ^(class4 == LEFT));
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}
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/**
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* Determines whether a point is on a line segment
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* @param a The start point of a line
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* @param b The end point of a line
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* @param c The test point
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*/
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static bool isOnLine(const Vertex &a, const Vertex &b, const Vertex &c) {
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// The items must all be Collinear, otherwise don't bothering testing the point
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if (triangleArea2(a, b, c) != 0) return false;
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// If the line segment is not vertical, check on the x-axis, otherwise the y-axis
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if (a.x != b.x) {
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return ((a.x <= c.x) &&
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(c.x <= b.x)) ||
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((a.x >= c.x) &&
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(c.x >= b.x));
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} else {
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return ((a.y <= c.y) &&
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(c.y <= b.y)) ||
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((a.y >= c.y) &&
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(c.y >= b.y));
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}
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}
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static bool isOnLineStrict(const Vertex &a, const Vertex &b, const Vertex &c) {
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// The items must all be Collinear, otherwise don't bothering testing the point
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if (triangleArea2(a, b, c) != 0) return false;
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// If the line segment is not vertical, check on the x-axis, otherwise the y-axis
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if (a.x != b.x) {
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return ((a.x < c.x) &&
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(c.x < b.x)) ||
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((a.x > c.x) &&
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(c.x > b.x));
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} else {
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return ((a.y < c.y) &&
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(c.y < b.y)) ||
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((a.y > c.y) &&
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(c.y > b.y));
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}
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}
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private:
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/**
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* Return double the size of the triangle defined by the three passed points.
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*
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* The result is positive if the points are arrange counterclockwise,
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* and negative if they are arranged counter-clockwise.
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*/
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static int triangleArea2(const Vertex &a, const Vertex &b, const Vertex &c) {
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return a.x * b.y - a.y * b.x +
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a.y * c.x - a.x * c.y +
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b.x * c.y - c.x * b.y;
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}
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};
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} // End of namespace Sword25
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#endif
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