void setup() {
size(600,300);
background(0);
}

void draw() {

rect(mouseX, mouseY, 50, 50);
fill(0);
stroke(255);
strokeWeight(3);
smooth();

rect(mouseX+20, mouseY+20, 50, 50);
fill(255);
stroke(1);
strokeWeight(2);

if (mousePressed) {
background(0);

ellipse(mouseX, mouseY, 50, 50);
fill(255);
stroke(0, 0, 255);
strokeWeight(3);
}
for (int i=0; i<600; i=i+20) {
line(0, 300, 300, i);
}
for (int i=0; i<600; i=i+20) {
line(600, 300, 300, i);

}
}