プロセシング

void setup(){

  size(500,500);

  frameRate(20);

}

void draw(){

  fadeToWhite();

  fill(mouseX + mouseY,0,0);

  stroke(0);

  ellipse(500/2,500/2,mouseX,mouseY);

}

void mousePressed(){

  fill(0);

  triangle(500/2,500-100,500/2 + 100,500,500/2 - 100,500);

void fadeToWhite(){

  noStroke();

  fill(255,30);

  rectMode(CORNER);

  rect(0,0,width,height);

}