Processing: collition2

衝突でボールが離れなくなるバグ有り

float X1, X2, Y1, Y2;
float Spx1, Spy1, Spx2, Spy2;
int r;

void setup(){
  size(400, 400);
  colorMode(HSB, 100);
  X1 = random(r, width-r);
  X2 = random(r, width-r);
  Y1 = random(r, height-r);
  Y2 = random(r, height-r);
  Spx1 = 5;
  Spy1 = Spx1;
  Spx2 = 3;
  Spy2 = -Spx2;
  r = 20;
  frameRate(60);
  smooth();
}

void draw(){
  fadeToWhite(99, 100);

  bounce();
  collide();
  X1 += Spx1;
  Y1 += Spy1;
  X2 += Spx2;
  Y2 += Spy2;
 
  fill(90, 60, 60, 90);
  ellipse(X1, Y1, r*2, r*2);
  fill(40, 60, 60, 90);
  ellipse(X2, Y2, r*2, r*2);
}

void bounce() {
  if (X1 <= r || X1 >= width-r){
    Spx1 = -Spx1;
    if (X1 <= r) { X1 = 2*r - X1; }
    if (X1 >= width-r) { X1 = 2*(width-r) - X1; }
  }
  if (X2 <= r || X2 >= width-r){
    Spx2 = -Spx2;
    if (X2 <= r){ X2 = 2*r - X2; }
    if (X2 >= width-r) { X2 = 2*(width-r) - X2; }
  }
  if (Y1 <= r || Y1 >= height-r){
    Spy1 = -Spy1;
    if (Y1 <= r) { Y1 = 2*r - Y1; }
    if (Y1 >= height-r) { Y1 = 2*(height-r) - Y1; }
  }
  if (Y2 <= r || Y2 >= height-r){
    Spy2 = -Spy2;
    if (Y2 <= r){ Y2 = 2*r - Y2; }
    if (Y2 >= height-r) { Y2 = 2*(height-r) - Y2; }
  }
}

void collide() {
  float dd = dist(X1, Y1, X2, Y2);
  float min = r * 2;
  if (dd <= min){
    Spx1 = -Spx1;
    Spy1 = -Spy1;
    Spx2 = -Spx2;
    Spy2 = -Spy2;
    X1 = X1 - (min - dd);
    X2 = X2 - (min - dd);
    Y1 = Y1 - (min - dd);
    Y2 = Y2 - (min - dd);
  }
}

void fadeToWhite(int max_color, float fade_speed) {
  noStroke();
  fill(max_color, fade_speed);
  rectMode(CORNER);
  rect(0, 0, width, height);
}