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【Java】 java判断点在三角形内
作者:周明瑞 / 发布于2013/2/1/ 639
package com.mingrui.soft_struct;

import java.awt.geom.Line2D;

public class Triangle2D{
	private MyPoint p0;
	private MyPoint p1;
	private MyPoint p2;
	
	Triangle2D(){
		this(0.0,0.0,1.0,1.0,2.0,5.0);
	}
	Triangle2D(double x,double y,double x1,double y1,double x2,double y2){
		p0=new MyPoint(x,y);
		p1=new MyPoint(x1,y1);
		p2=new MyPoint(x2,y2);
	}
	public MyPoint getP0(){
		return p0;
	}
	public MyPoint getP1(){
		return p1;
	}
	public MyPoint getP2(){
		return p2;
	}
	public double getArea(){
		double p=getPerimeter()/2.0;
		return Math.sqrt(p*
		(p-MyPoint.distance(p0,p1))*
		(p-MyPoint.distance(p1,p2))*
		(p-MyPoint.distance(p0,p2)));
	}
	public double getPerimeter(){
		return MyPoint.distance(p0,p1)+MyPoint.distance(p1,p2)+MyPoint.distance(p2,p0);
	}	
	public int contains(MyPoint p){
		/*
		0. in the line 
		1.is a point 
		2.in the triangle
		3.out of the triangle
		*/	
		Line2D.Double ld = new Line2D.Double(p0.getX(), p0.getY(), p1.getX(), p1.getY());
		Line2D.Double ld1 = new Line2D.Double(p1.getX(), p1.getY(), p2.getX(), p2.getY());
		Line2D.Double ld2 = new Line2D.Double(p0.getX(), p0.getY(), p2.getX(), p2.getY());
		Line2D.Double ld3 = new Line2D.Double(p0.getX(), p0.getY(), p.getX(), p.getY());
		Line2D.Double ld4 = new Line2D.Double(p1.getX(), p1.getY(), p.getX(), p.getY());
		Line2D.Double ld5 = new Line2D.Double(p2.getX(), p2.getY(), p.getX(), p.getY());
		if(ld.contains(p.getX(), p.getY())||ld1.contains(p.getX(), p.getY())||ld2.contains(p.getX(), p.getY()))
			return 0;
		if(LineUtil.isAPoint(p0, p1, p2, p))
			return 1;
		if(ld.intersectsLine(ld5))
			return 3;
		else if(ld1.intersectsLine(ld3))
			return 3;
		else if(ld2.intersectsLine(ld4))
			return 3;
		else if(ld.ptLineDist(p.getX(), p.getY())<ld.ptLineDist(p2.getX(),p2.getY())
			&&ld1.ptLineDist(p.getX(), p.getY())<ld1.ptLineDist(p0.getX(),p0.getY())
			&&ld2.ptLineDist(p.getX(), p.getY())<ld2.ptLineDist(p1.getX(),p1.getY()))
			return 2;
		else
			return 3;
	}
	public void overlaps(Triangle2D t){
		int i=contains(t.getP0());
		int j=contains(t.getP1());
		int k=contains(t.getP2());
		/*
		 * 0. in the line 
		 * 1.is a point 
		 * 2.in the triangle
		 * 3.out of the triangle
		*/	
		if(i==3&&j==3&&k==3){
			System.out.println("out of the triangle");
		}
		else
			System.out.println("in the triangle");
		//return false;
	}

	public static void main(String args[]){
		Triangle2D t1=new Triangle2D();
		Triangle2D t2=new Triangle2D();
		MyPoint p=new MyPoint(1,1.3);
		System.out.println(t1.contains(p));
		t1.overlaps(t2);
	}
}

class MyPoint{
	private double x;
	private double y;
	MyPoint(){
		this.x=0;
		this.y=0;
	}
	MyPoint(double x,double y){
		this.x=x;
		this.y=y;
	}
	public double getX(){
		return x;
	}
	public double getY(){
		return y;
	}
	public static double distance(MyPoint p,MyPoint p1){
		return Math.sqrt((p.getX()-p1.getX())*(p.getX()-p1.getX())+(p.getY()-p1.getY())*(p.getY()-p1.getY()));
	}
	public static double distance(int x,int y,int x1,int y1){
		return Math.sqrt((x-x1)*(x-x1)+(y-y1)*(y-y1));
	}
}

class LineUtil{
	public static double getK(MyPoint p0,MyPoint p1){
		return (p0.getY()-p1.getY())/(p0.getX()-p1.getX());
	}
	public static double getK(MyPoint p0,double x,double y){
		return (p0.getY()-y)/(p0.getX()-x);
	}
	public static boolean isAPoint(MyPoint p0,MyPoint p1,MyPoint p2,MyPoint thePointToTest){
		if((p0.getX()==thePointToTest.getX()&&p0.getY()==thePointToTest.getY())
		||(p1.getX()==thePointToTest.getX()&&p1.getY()==thePointToTest.getY())
		||(p2.getX()==thePointToTest.getX()&&p2.getY()==thePointToTest.getY())){
			return true;
		}
		else 
			return false;
	}
}
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