Collision detection

hi

I am trying to get the ball to bounce off my paddle like in the coding challenge ‘pong’ video. I have followed step by step and the ball is bouncing off random parts of the page and not off my paddle.

can somebody help me plz



import org.gamecontrolplus.gui.*;
import org.gamecontrolplus.*;
import net.java.games.input.*;

ControlIO control;
ControlDevice stick;


Ball ball;
Paddle center;

int score;
String s;
boolean intersect;
float px;
boolean trailOn;
PImage img;
ArrayList<PVector>  shadows = new ArrayList<PVector>();
ArrayList<PVector>  trail = new ArrayList<PVector>();
 
public void setup() {
    size(1000, 700);
  ball = new Ball();
  center = new Paddle(true);
  img = loadImage("Gun.png");
  
  
  
   // Initialise the ControlIO
  control = ControlIO.getInstance(this);
  // Find a device that matches the configuration file
  stick = control.getMatchedDevice("joystick");
  if (stick == null) {
    println("No suitable device configured");
    System.exit(-1); // End the program NOW!
  }
  // Setup a function to trap events for this button
  stick.getButton("SHADOW").plug(this, "dropShadow", ControlIO.ON_RELEASE);
}

// Poll for user input called from the draw() method.
public void getUserInput() {
  px = map(stick.getSlider("X").getValue(), -1, 1, 0, width);
  //py = map(stick.getSlider("Y").getValue(), -1, 1, 0, height);
  trailOn = stick.getButton("TRAIL").pressed();
}


/// Event handler for the SHADOW button
public void dropShadow() {
  // Make sure we have the latest position
  getUserInput();
  shadows.add(new PVector(px, 40));
}
public void draw() {
  getUserInput(); // Polling
  background(255, 255, 240);
  
 
  
  // Draw shadows
     for (PVector shadow : shadows)
    ellipse(shadow.x, shadow.y, shadow.z, shadow.z);
    if (trailOn) 
   trail.add(new PVector());
  else
    trail.clear();
  if (trail.size() > 1) {
    stroke(132, 0, 0);
    for (int n = 1; n < trail.size(); n++) {
      PVector v0 = trail.get(n-1);
      PVector v1 = trail.get(n);
      line(v0.x, v0.y, v1.x, v1.y);
      v0 = v1;
    
    
    
  }
 }

  
  ball.checkPaddle(center);
  center.update();
  center.show();
  ball.show();
  ball.update();
  ball.edges();
  
}
class Ball {
  float x = width/5;
  float y = height/15;
  float xspeed = 3;
  float yspeed = 3;
  float r = 12;
  Ball(){
   
  }
  void checkPaddle(Paddle px){
    if (y < px.y + px.h/2 && y > px.y - px.h/2 && x - r  < px.x + px.w/2){
     // if (x < px.x + px.w/2 && x > px.x - px.x/2 && y - r  < px.y + px.h/2){
     
         xspeed *=-1;
      }
      
      
 
      
  
  }
  
  void update(){
    x = x + xspeed;
    y = y + yspeed;
  }
  
  void reset(){
    x = random(width);
    y = height/15;
  }
  
  void edges(){
    if (x < 0 ||x > width){
      xspeed *=-1;
    }
    
    if(y > height){
      reset();
    }
    if (y < 0){
      reset();
  }
  }
  void show(){
    fill(150);
    ellipse (x,y,r*2,r*2);
  }
}class Paddle{
  float x;
  float y = height/2;
 float w = 1000;
 float h = 1;
  
  float ychange = 0;
  
  void update(){
    y+= ychange;
    y = constrain(y,h/2, height-h/2);
  }
  
  void move(float steps){
    ychange = steps;
  }
  
  Paddle(boolean center){
    if(center){
    x = w/2;
    } else {
      x = width - w;
    }
 
   
    
  }
  void show(){
    
noStroke();
 
 imageMode(CENTER);
image(img,px,700, 300,300);
//fill(255);
//rectMode(CENTER);
//rect(px, 700, 100, 200);


}







}
1 Like

you are aware that for
https://thecodingtrain.com/CodingChallenges/067-pong.html
the code is available
https://github.com/CodingTrain/website/tree/master/CodingChallenges/CC_067_Pong/Processing/CC_067_Pong ,


also i think you need to check on
the disabled line / your modifications? / inside

 void checkPaddle(Paddle px)
2 Likes

thankyou i will give this a try

I realize you’re looking for a specific fix to your problem, but I would recommend checking this out:

This is an excellent resource for both getting your head around how collision detection works. It explains the problem
in simple terms, describes how to solve it, and provides a solution in the form of example code.

Since you already have partially working code, there is probably either a bug in the basic logic, a missing edge case, or some underlying assumption that is false.

I’m guessing if you have no paddle collision then the ball (or rather the point (x-r, y) is never actually inside the test boundaries) when you check. Also in the code you provided I think the ball will only ever bounce off the left side of the paddle AND when it’s center’s y-coord is between:
px.y - px.h / 2 and px.y + px.h / 2
When and if it does bounce you are only modifying xspeed, and not yspeed.

You might want circle-rectangle collision instead of point-rectangle.

2 Likes