how to make circular surface in pygame

Question

I need to create a surface that has a bounding circle. Anything drawn on that surface should not be visible outside that bounding circle. I\'ve tried using masks, subsurfaces, s

Answer 1

The background is a square image. It should be cropped into the shape of a circle and rendered on screen

You can achieve this by using the blend mode BLEND_RGBA_MIN (see pygame.Surface.blit).

Create a transparent pygame.Surface with the same size as self.background. Draw a whit circle in the middle of the Surface and blend the background on this Surface using the blend mode BLEND_RGBA_MIN. Finally you can blit it on the screen:

size = self.background.get_size()
self.cropped_background = pygame.Surface(size, pygame.SRCALPHA)
pygame.draw.ellipse(self.cropped_background, (255, 255, 255, 255), (0, 0, *size))
self.cropped_background.blit(self.background, (0, 0), special_flags=pygame.BLEND_RGBA_MIN)

self.ss.fill(BLACK)
self.ss.blit(self.cropped_background, ORIGIN)

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Minimal example: repl.it/@Rabbid76/PyGame-ClipCircularRegion-1

import pygame
pygame.init()
window = pygame.display.set_mode((250, 250))

background = pygame.Surface(window.get_size())
for x in range(5):
    for y in range(5):
        color = (255, 255, 255) if (x+y) % 2 == 0 else (255, 0, 0)
        pygame.draw.rect(background, color, (x*50, y*50, 50, 50))

size = background.get_size()
cropped_background = pygame.Surface(size, pygame.SRCALPHA)
pygame.draw.ellipse(cropped_background, (255, 255, 255, 255), (0, 0, *size))
cropped_background.blit(background, (0, 0), special_flags=pygame.BLEND_RGBA_MIN)

run = True
while run:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
        
    window.fill(0)
    window.blit(cropped_background, (0, 0))
    pygame.display.flip()

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See Also How to fill only certain circular parts of the window in pygame?