gfxdraw.circle, .aacircle, .filled_circle, .arc and .pie all add a central pixel, making circles 1 px too big. (2924)

[GalacticEmperor1]

Issue №2924 opened by flodri at 2021-12-17 17:50:02

Environment:

• Operating system (e.g. Windows, Linux(Debian), Linux(Ubuntu), Mac): Windows 10
• Python version (e.g. 3.7.9, 3.8.5) : 3.7.8
• SDL version (e.g. SDL 2.0.12): 2.0.16
• PyGame version (e.g. 2.0.0.dev10, 1.9.6): 2.1.0

Current behavior:

gfxdraw.circle, .aacircle, .filled_circle, .arc and .pie all add a central pixel that shouldn't be here, making the circles 1 pixel too big to the right and bottom.
So for exemple a 16 px radius circle will actually be draw as a 16.5 px radius circle and fit in a 33x33 box instead of 32x32.

Expected behavior:

What draw.circle does, circles of the correct dimension.

Steps to reproduce:

1. use gfxdraw.circle, .aacircle, .filled_circle, .arc or .pie to draw a circle
2. see that they're 1 pixel too big to the right and bottom

Test code

import pygame
import pygame.gfxdraw
pygame.init()
screen = pygame.display.set_mode((128, 128))

pygame.draw.rect(screen, (255, 0, 0), (32, 32, 64, 64)) #  bouding box if the circle was the correct size
pygame.gfxdraw.circle(screen, 64, 64, 32, (0, 255, 0))

running = True
while running:
    events = pygame.event.get()
    for event in events:
        if (event.type == pygame.KEYDOWN and event.key == pygame.K_ESCAPE) or (event.type == pygame.QUIT):
            running = False
    pygame.display.flip()

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Comments

# # ankith26 commented at 2021-12-31 04:29:21

Thanks for the bug report! This is something we should fix while porting gfxdraw functions to pygame.draw. gfxdraw is a vendored library, that is not well maintained these days

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# # Starbuck5 commented at 2022-05-02 08:22:15

I believe it's that the underlying circle algorithm only draws odd numbered widths and heights. So it's only one pixel off half the time No, you're right, it's 1 pixel off all the time.

I propose we add a small note to the docs documenting this behavior, then close this issue (sortof as a wontfix), because I don't believe pygame wants to mess with SDL_gfx functions just for this.