int frame=0;
boolean doSave;

void setup() {
  size(400,400);
  ellipseMode(CENTER_DIAMETER);  
  doSave=false;
}

void loop() {
  background(200,0,100);
  ellipse(150,150, 50,50);
  ellipse(random(width),random(height), 30,30);

  if(doSave) {
    saveFrame("animation1_"+frame+".tif");
    println("Saved 'animation1_"+frame+".tif'");
    frame++;
    doSave=false;
  }
}

void mousePressed() {
  doSave=true;
}