Inspiration Code

This code has been helpful in the learning process of collisions.
When the smaller circle collides with the larger circle the colour changes, this collision shows a change when other objects interact within its radius, it has showed me that to find the collision is to find the centre points and if the distance between the two centre points are small the the sum of the two radius' we have a collision. 




/*
BALL/BALL COLLISION DETECTION
 Jeff Thompson
 Fall 2011

 www.jeffreythompson.org
 */


int youX, youY;        // x,y position of "you"
int youSize = 30;      // assumes a circle - elliptical collision is VERY complicated
int speed = 2;         // speed to move you around


int ballX, ballY;      // x,y position of the ball - will be randomly placed in the setup
int ballSize = 100;    // assumes a circle - elliptical collision is VERY complicated




void setup() {


  size(400, 400);
  smooth();
  noStroke();



  youX = width/2;
  youY = height/2;



  ballX = int(random(ballSize, width-ballSize));
  ballY = int(random(ballSize, height-ballSize));
}


void draw() {


  
  background(255);


  // TEST FOR COLLISION
  // returns true if hit, false if not
  if (ballBall(youX, youY, youSize, ballX, ballY, ballSize) == true) {
    fill(0);
  }
  else {
    fill(200);
  }


  
  ellipse(ballX, ballY, ballSize, ballSize);


  
  fill(0);
  ellipse(youX, youY, youSize,youSize);


  // IF ARROW KEYS ARE PRESSED, UPDATE "YOU" POSITION
  if (keyPressed) {
    if (key == CODED) {
      if (keyCode == LEFT) {
        youX -= speed;
      }
      if (keyCode == RIGHT) {
        youX += speed;
      }
      if (keyCode == UP) {
        youY -= speed;
      }
      if (keyCode == DOWN) {
        youY += speed;
      }
    }
  }
}


/* 
 BALL/BALL COLLISION FUNCTION
 Takes 6 arguments:
 + x,y position of the first ball - in this case "you"
 + diameter of first ball - elliptical collision is VERY difficult
 + x,y position of the second ball
 + diameter of second ball

 */
boolean ballBall(int x1, int y1, int d1, int x2, int y2, int d2) {


  // find distance between the two objects
  float xDist = x1-x2;                                   // distance horiz
  float yDist = y1-y2;                                   // distance vert
  float distance = sqrt((xDist*xDist) + (yDist*yDist));  // diagonal distance


  // test for collision
  if (d1/2 + d2/2 > distance) {
    return true;    // if a hit, return true
  }
  else {            // if not, return false
    return false;
  }
}