跳ね返るボールのサンプル

gistfile1.pde

float FRICTION = 0.99;

float x, y;
float speedY, speedX;
int radius = 10;

void setup(){
  size(200, 200);
  colorMode(HSB, 100);
   background(99);
   noStroke();
   frameRate(15);
   
   x = width/2;
   y = height/2;
   speedY = random(-30, 30);
   speedX = random(-30, 30);
}

void draw(){
  //background(99);
  fadeToWhite();
  speedX = speedX * FRICTION;
  speedY = speedY * FRICTION;
  x += speedX;
  y += speedY;
  
  bounce();
  
  fill(0);
  ellipse(x,y, radius*2, radius*2);
}

void bounce() {
  float bounceMinX = radius;  
  float bounceMaxX = width - radius;
  float bounceMinY = radius;
  float bounceMaxY = height - radius;
  
  if(x < bounceMinX || x > bounceMaxX){
    speedX = -speedX;
    if(x < bounceMinX) x = bounceMinX - (x - bounceMinX);
    if(x > bounceMaxX) x = bounceMaxX - (x - bounceMaxX);
  }
  
  if(y < bounceMinY || y > bounceMaxY){
    speedY = -speedY;
    if(y < bounceMinY) y = bounceMinY - (y - bounceMinY);
    if(y > bounceMaxY) y = bounceMaxY - (y - bounceMaxY);
  }
}

void fadeToWhite() {
  noStroke();
  fill(99, 60);
  rectMode(CORNER);
  rect(0,0,width, height);
}