int i;

size(300,300);

for(i=0;i<300;i=i+10){
 rect(i,295-i,5,5);
 stroke(i,0,0);
 line(i,0,i,300);
 line(0,0,300,i);
 fill(i,0,0);
 rect(i,i,5,5);
 rect(i+10,i,5,5);
}