int diameter = 0;
int stipKleur = #FF4141;

void setup()
{
  size(500, 300);
}

void draw()
{
  background(#FFFF41);
  noStroke();
  fill(stipKleur); //kleur
  ellipse(300, 150 ,diameter, diameter); //cirkel+plek
}

void mouseDragged()
{
  diameter = mouseX/2+mouseY/2;
}