void setup() {
	size(500, 500);
	frameRate(20);
	background(255);
}

void draw() {
	fadeToWhite();
	stroke(mouseX, 0, mouseY);
	ellipse(mouseX, mouseY, 10, 10);
}

void fadeToWhite() {
	noStroke();
	fill(255, 10);
	rectMode(CORNER);
	rect(0, 0, width, height);
}