像风一样
int xf = (int) random(width);
int yf = (int) random(height);
int x = (int) random(width);
int y = (int) random(height);
background(0xFF);
while(x != xf || y != yf) {
set(x,y,color(0,0,0));
x = max(0, min(x + -1 + (int) random(3), width - 1) );
y = max(0, min(y + -1 + (int) random(3), height - 1) );
}