fullscreen void setup(){
size(250,250);
smooth();
background(255);
}
void draw(){
fill(0,5);
noStroke();
rect(20,20,210,210);
fill(255);
rect(0,0,20,250);
rect(0,0,250,20);
rect(230,0,20,250);
rect(230,230,250,20);
}
void mousePressed(){
stroke(random(255),random(255),random(255));
strokeWeight(random(5));
line(20,random(230),230,random(230));
}