int green = 255;
int tiempo = 0;
int diametro = 50;

void setup() {
size(400, 400);
}

void draw() {
tiempo = tiempo + 1;
green = int(128 * (1 + sin(tiempo * 2 * PI / frameRate / 20)));
diametro = int(50 * (1 + sin(tiempo * 2 * PI / frameRate / 5)));

noStroke();
fill(0,green,0);                  
ellipse(mouseX, mouseY, diametro, diametro);
}