在pygame中将screen.fill设置为渐变？

import pygame

def gradient_fill(screen, start_color, end_color):
    width, height = screen.get_size()
    start_rgb = pygame.Color(start_color)
    end_rgb = pygame.Color(end_color)

    for y in range(height):
        start_r = start_rgb.r + (end_rgb.r - start_rgb.r) * y / height
        start_g = start_rgb.g + (end_rgb.g - start_rgb.g) * y / height
        start_b = start_rgb.b + (end_rgb.b - start_rgb.b) * y / height
        start_color = (start_r, start_g, start_b)

        for x in range(width):
            screen.set_at((x, y), start_color)

pygame.init()
screen = pygame.display.set_mode((800, 600))
start_color = "red"
end_color = "blue"

gradient_fill(screen, start_color, end_color)

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    pygame.display.flip()

pygame.quit()