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int d=0;
int r=255;
void setup() {
size(400, 400);
background(0);
}
void draw() {
if(mousePressed) {
noFill();
stroke(r);
ellipse(width/2, height/2, d, d);
d = d +1;
r = r - 1;
if(r < 0) {
d = 0;
r = 255;
}
}
}