A
var N = 30;
var a = 30;
function setup() {
createCanvas(N * a, N * a);
background(0, 0, 255);
stroke(250, 250, 150);
noFill();
rectMode(CENTER);
for (var n = 0; n <= N; n++) {
if (n < N * 0.5) {
rect(N * a * 0.5, N * a * 0.5, N * a - n * a, N * a - n * a);
}
line(n * a, 0, n * a * 0.5 + N * a * 0.25, N * a * 0.25);
line(n * a, N * a, n * a * 0.5 + N * a * 0.25, N * a * 0.75);
line(0, n * a, N * a * 0.25, n * a * 0.5 + N * a * 0.25);
line(N * a, n * a, N * a * 0.75, n * a * 0.5 + N * a * 0.25);
line(n * a * 0.5 + N * a * 0.25, N * a * 0.25, n * a * 0.5 + N * a * 0.25, N * a * 0.75);
line(N * a * 0.25, n * a * 0.5 + N * a * 0.25, N * a * 0.75, n * a * 0.5 + N * a * 0.25);
}
}