cross

cross.py

from PIL import Image, ImageDraw
import numpy as np

L = 1028

img = Image.new('RGBA', (L, L), (255, 0, 0, 0))
center = (L / 2, L / 2)

def scale_w_by_d(d):
    return int(d / (L / 2) * 32)

def scale_alpha_by_d(d):
    return 255 - int(d / (L / 2) * 255)

draw = ImageDraw.Draw(img)
for i in np.linspace(0, L, 17):
    for j in np.linspace(0, L, 17):
        dd = np.sqrt((i - L / 2) ** 2 + (j - L / 2) ** 2)
        if dd > L / 2:
            continue

        delx, dely = center[0] - i, center[1] - j
        l = np.sqrt(delx ** 2 + dely ** 2)

        # edge case
        if l == 0: continue

        delx_norm, dely_norm = delx / l * 32 , dely / l * 32
        end_i, end_j = i + delx_norm, j + dely_norm

        ww = scale_w_by_d(dd)
        aa = scale_alpha_by_d(dd)
        draw.line((i, j, end_i, end_j), fill=(255, 0, 0, aa), width=ww)

img.save('cross.png', 'PNG')