Fading effect in pygame using a blit from a surface based on a bytearray

pygame_blit_from_bytearray.py

"""
A fading effect created by manipulating a bytearray that underlies a Surface object
"""

import math, pygame

def main():
    pygame.init()
    size = width, height = 320, 240
    screen = pygame.display.set_mode(size)
    pygame.display.set_caption("Blit from bytearray")
    clock = pygame.time.Clock()
    bytes_image = bytearray(width * height * 4)
    picture = pygame.image.frombuffer(bytes_image, size, 'RGBA')
    frame = 0

    main_surface = pygame.display.get_surface()
    rays = list()
    num_rays = 200
    for i in range(num_rays):
        # x, y, vx, vy
        phi = 2 * math.pi / num_rays * i
        rays.append([width/2, height/2, math.cos(phi), math.sin(phi)])

    def set_color(x, y, color):
        i = (y * width + x) * 4
        bytes_image[i+0] = color.r
        bytes_image[i+1] = color.g
        bytes_image[i+2] = color.b
        bytes_image[i+3] = 255

    # bg_surface = pygame.image.load('bg320x240.jpg')
    def get_bg_color(x, y):
        # return bg_surface.get_at((int(x), int(y)))
        # simple gradient:
        u = x / width
        v = y / height
        return pygame.Color(int(u * 255) % 255,
                            int(v * 255) % 255,
                            int((1 - u) * 255) % 255,
                            255)

    while True:
        clock.tick(60)
        for event in pygame.event.get():
            if event.type == pygame.QUIT or event.type == pygame.KEYDOWN:
                return

        for ray in rays:
            x,y,vx,vy = ray
            x += vx
            if x < 0 or x >= width:
                x -= vx
                vx *= -1
            y += vy
            if y < 0 or y >= height:
                y -= vy
                vy *= -1
            set_color(int(x), int(y), get_bg_color(x, y))
            ray[0] = x
            ray[1] = y
            ray[2] = vx
            ray[3] = vy

        main_surface.blit(picture, (0, 0))

        pygame.display.flip()
        frame += 1

if __name__ == '__main__':
    main()

https://imgur.com/a/fUsVgRQ