boolean black=false;

void setup() {
smooth();
size(500, 500);
strokeWeight(8);
}

void draw() {
background(255);
noStroke();
fill(0);
rect(mouseX, mouseY, random(100), random(100));
frameRate(12);
if (black) background(0);
}

void mouseClicked () {
black = !black;

}

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