libgdx学习记录27——线段与线段相交检测

给定p1, p2, p3, p4四个点，p1,p2为一条线段，p3,p4为一条线段，检测其是否有交点。

可分为三种情况：

1. L2与x轴平行

2. L2与y轴平行

3. L2与坐标轴不平行。

（L1与坐标轴平行，类似处理）

基本思路，求出交点坐标，并检测其是否在两个线段内即可。

检测代码：

     public static float min(float x, float y) { return x<y? x: y; }
     public static float max(float x, float y) { return x>y? x: y; }

     public static boolean isSegmentOverlap(Vector2 p1, Vector2 p2, Vector2 p3, Vector2 p4){
         if(p3.x == p4.x){
             float x = p3.x;
             float y = p1.y + (p3.x-p1.x)*(p2.y-p1.y)/(p2.x-p1.x);
             //System.out.println(y);
             if( x>min(p1.x, p2.x) && x<max(p1.x, p2.x)  &&  y>min(p1.y, p2.y) && y<max(p1.y, p2.y)  &&
                 x>=min(p3.x, p4.x) && x<=max(p3.x, p4.x)  &&  y>min(p3.y, p4.y) && y<max(p3.y, p4.y)    ){
                 return true;
             }
         }
         else if(p3.y == p4.y){
             float x = p1.x + (p3.y-p1.y)*(p2.x-p1.x)/(p2.y-p1.y);
             float y = p3.y;
             if( x>min(p1.x, p2.x) && x<max(p1.x, p2.x)  &&  y>min(p1.y, p2.y) && y<max(p1.y, p2.y)  &&
                 x>min(p3.x, p4.x) && x<max(p3.x, p4.x)  &&  y>=min(p3.y, p4.y) && y<=max(p3.y, p4.y) ){
                 return true;
             }
         }
         else if(p1.x==p2.x || p1.y==p2.y){
             return isSegmentOverlap(p3, p4, p1, p2);
         }
         else{
             float k1 = (p2.y-p1.y)/(p2.x-p1.x);
             float k2 = (p4.y-p3.y)/(p4.x-p3.x);
             float x = (k2*p3.x-k1*p1.x+p1.y-p3.y)/(k2-k1);
             float y = k1*(x-p1.x) + p1.y;
             //System.out.println( k1 + "," + k2 + "," + x + "," + y );
             if( x>min(p1.x, p2.x) && x<max(p1.x, p2.x)  &&  y>min(p1.y, p2.y) && y<max(p1.y, p2.y)  &&
                 x>min(p3.x, p4.x) && x<max(p3.x, p4.x)  &&  y>min(p3.y, p4.y) && y<max(p3.y, p4.y) ){
                 return true;
             }
         }

         return false;
     }

实例代码：

 package com.fxb.Gam003;

 import com.badlogic.gdx.ApplicationAdapter;
 import com.badlogic.gdx.Gdx;
 import com.badlogic.gdx.InputAdapter;
 import com.badlogic.gdx.graphics.Color;
 import com.badlogic.gdx.graphics.GL10;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType;
 import com.badlogic.gdx.math.Rectangle;
 import com.badlogic.gdx.math.Vector2;
 import com.badlogic.gdx.scenes.scene2d.InputListener;

 public class Lib054_SegmentOverlap extends ApplicationAdapter{

     ShapeRenderer rend;

     Vector2 p1 = new Vector2(300, 100);
     Vector2 p2 = new Vector2(500, 200);
     Vector2 p3 = new Vector2(300, 200);
     Vector2 p4 = new Vector2(400, 300);

     Rectangle rect = new Rectangle( 100, 100, 200, 200 );

     @Override
     public void create() {
         // TODO Auto-generated method stub
         super.create();

         rend = new ShapeRenderer();
         Gdx.input.setInputProcessor(adapter);
     }

     public static float min(float x, float y) { return x<y? x: y; }
     public static float max(float x, float y) { return x>y? x: y; }

     public static boolean isSegmentOverlap(Vector2 p1, Vector2 p2, Vector2 p3, Vector2 p4){
         if(p3.x == p4.x){
             float x = p3.x;
             float y = p1.y + (p3.x-p1.x)*(p2.y-p1.y)/(p2.x-p1.x);
             //System.out.println(y);
             if( x>min(p1.x, p2.x) && x<max(p1.x, p2.x)  &&  y>min(p1.y, p2.y) && y<max(p1.y, p2.y)  &&
                 x>=min(p3.x, p4.x) && x<=max(p3.x, p4.x)  &&  y>min(p3.y, p4.y) && y<max(p3.y, p4.y)    ){
                 return true;
             }
         }
         else if(p3.y == p4.y){
             float x = p1.x + (p3.y-p1.y)*(p2.x-p1.x)/(p2.y-p1.y);
             float y = p3.y;
             if( x>min(p1.x, p2.x) && x<max(p1.x, p2.x)  &&  y>min(p1.y, p2.y) && y<max(p1.y, p2.y)  &&
                 x>min(p3.x, p4.x) && x<max(p3.x, p4.x)  &&  y>=min(p3.y, p4.y) && y<=max(p3.y, p4.y) ){
                 return true;
             }
         }
         else if(p1.x==p2.x || p1.y==p2.y){
             return isSegmentOverlap(p3, p4, p1, p2);
         }
         else{
             float k1 = (p2.y-p1.y)/(p2.x-p1.x);
             float k2 = (p4.y-p3.y)/(p4.x-p3.x);
             float x = (k2*p3.x-k1*p1.x+p1.y-p3.y)/(k2-k1);
             float y = k1*(x-p1.x) + p1.y;
             //System.out.println( k1 + "," + k2 + "," + x + "," + y );
             if( x>min(p1.x, p2.x) && x<max(p1.x, p2.x)  &&  y>min(p1.y, p2.y) && y<max(p1.y, p2.y)  &&
                 x>min(p3.x, p4.x) && x<max(p3.x, p4.x)  &&  y>min(p3.y, p4.y) && y<max(p3.y, p4.y) ){
                 return true;
             }
         }

         return false;
     }

     public static boolean isSegRectOverlap(Vector2 p1, Vector2 p2, Rectangle rect){
         float x = rect.x, y = rect.y, w = rect.width, h = rect.height;
         Vector2 rp1 = new Vector2(x, y);
         Vector2 rp2 = new Vector2(x+w, y);
         Vector2 rp3 = new Vector2(x+w, y+h);
         Vector2 rp4 = new Vector2(x, y+h);
         //return isSegmentOverlap(p1, p2, rp1, rp2) || isSegmentOverlap(p1, p2, rp2, rp3) ||
         //        isSegmentOverlap(p1, p2, rp3, rp4) || isSegmentOverlap(p1, p2, rp4, rp1);

         if( rect.contains(p1) || rect.contains(p2) ){
             return true;
         }

         return isSegmentOverlap(p1, p2, rp1, rp2) || isSegmentOverlap(p1, p2, rp2, rp3) ||
                 isSegmentOverlap(p1, p2, rp3, rp4) || isSegmentOverlap(p1, p2, rp4, rp1);
     }

     @Override
     public void render() {
         // TODO Auto-generated method stub
         super.render();
         Gdx.gl.glClearColor(1, 1, 1, 1);
         Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

         rend.begin(ShapeType.Line);

         if(isSegmentOverlap(p1, p2, p3, p4)){
             rend.setColor(Color.RED);
         }
         else{
             rend.setColor(Color.BLUE);
         }
         rend.line(p1, p2);
         rend.line(p3, p4);

 //        if(isSegRectOverlap(p1, p2, rect)){
 //            rend.setColor(Color.RED);
 //        }
 //        else{
 //            rend.setColor(Color.BLUE);
 //        }
 //        rend.line(p1, p2);
 //        rend.rect(rect.x, rect.y, rect.width, rect.height);

         rend.end();

     }

     @Override
     public void dispose() {
         // TODO Auto-generated method stub
         super.dispose();
     }

     InputAdapter adapter = new InputAdapter(){
         @Override
         public boolean touchDown(int screenX, int screenY, int pointer, int button) {
             p1.set(screenX, 480-screenY);
             return super.touchDown(screenX, screenY, pointer, button);
         }

         @Override
         public boolean touchDragged(int screenX, int screenY, int pointer) {
             p2.set(screenX, 480-screenY);
             return super.touchDragged(screenX, screenY, pointer);
         }

         @Override
         public boolean touchUp(int screenX, int screenY, int pointer, int button) {
             p2.set(screenX, 480-screenY);
             return super.touchUp(screenX, screenY, pointer, button);
         }

     };

 }

运行结果：

 

显示两种状态，相交红色，不相交蓝色。