float x1, y1, x2, y2, x3, y3, x4, y4;
float vx1, vy1, vx2, vy2, vx3, vy3, vx4, vy4;

void setup() {
  size(400, 400);
  x1 = 100;
  y1 = 100;
  x2 = 100;
  y2 = 100;
  x3 = 100;
  y3 = 100;
  x4 = 100;
  y4 = 100;      
  
  vx1 = 2;
  vy1 = 3;
  vx2 = -2;
  vy2 = -3;
  vx3 = 1.2;
  vy3 = 2.3;
  vx4 = 3.2;
  vy4 = 1.3;      
  
}

void draw() {
  x1 = x1 + vx1;
  y1 = y1 + vy1;
  
  x2 = x2 + vx2;
  y2 = y2 + vy2;

  x3 = x3 + vx3;
  y3 = y3 + vy3;
  
  x4 = x4 + vx4;
  y4 = y4 + vy4;          
  
  if (x1 < 0 || x1 > width) {
    vx1 = -vx1;
  }
  if (y1 < 0 || y1 > height) {
    vy1 = -vy1;
  }  
  
  if (x2 < 0 || x2 > width) {
    vx2 = -vx2;
  }
  if (y2 < 0 || y2 > height) {
    vy2 = -vy2;
  }
  
  if (x3 < 0 || x3 > width) {
    vx3 = -vx3;
  }
  if (y3 < 0 || y3 > height) {
    vy3 = -vy3;
  }
  
  if (x4 < 0 || x4 > width) {
    vx4 = -vx4;
  }
  if (y4 < 0 || y4 > height) {
    vy4 = -vy4;
  }
  
  stroke(255, 0, 0);
  ellipse(x1, y1, 40, 40);
  
  stroke(0, 255, 0);
  ellipse(x2, y2, 40, 40);
  
  stroke(0, 0, 255);
  ellipse(x3, y3, 40, 40);
  
  stroke(0, 255, 255);
  ellipse(x4, y4, 40, 40);
   
}