Add draw.aaellipse

[mzivic7]

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This PR adds draw.aaellipse function, with width and thickness options. It is completely interchangeable with draw.ellipse in terms of arguments. Algorithm used is adapted from Xiaolin Wu's general fast antialiasing algorithm, and is very similar to draw.aacircle. Only notable difference: in aacircle, 8 pixels are drawn at once, but here, only 4, because ellipse has 2 symmetries. Because of that aaelipse has additional vertical drawing (aacircle has only horizontal but because of extra symmetries it is vertical at the same time). It is added to docs too.

Sample code

import pygame

pygame.init()
screen = pygame.display.set_mode((512, 512))
clock = pygame.time.Clock()

run = True
while run:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
    screen.fill("black")
    pygame.draw.aaellipse(screen, "red", [100, 100, 100, 50], 1)
    pygame.draw.aaellipse(screen, "red", [100, 160, 100, 50])
    pygame.draw.aaellipse(screen, "red", [100, 220, 100, 50], 4)
    pygame.display.flip()
    clock.tick(60)
pygame.quit()

[mzivic7]

Note: before merging, correct versionadded in docs/reST/ref/draw.rst, if needed.

[mzivic7]

I moved ellipse and aaellipse functions bellow circle and aacircle, because aacircle is called in aaellipse and aa* functions should always be bellow regular one.

[Starbuck5]

I see holes around the edges of the ellipse in this test case.

import pygame
screen = pygame.display.set_mode((600,600))
running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        if event.type == pygame.KEYDOWN and event.key == pygame.K_w:
            pygame.image.save(screen, "output.png")
    screen.fill("purple")
    pygame.draw.aaellipse(screen, "red", [100,200,300,400])
    pygame.display.flip()
pygame.quit()

[Starbuck5]

Other things I see.

• [x] pygame.draw.aaellipse(screen, "red", [100,200,30,200000], width=0) crashes the app
• [x] putting in a rect with negative dimensions leads to weird stuff being drawn
• [x] if the width and the height are equal the surface being drawn on cannot be blitted in the future (you forgot to unlock it in this case)

[coderabbitai[bot]]

📝 Walkthrough

Walkthrough

Adds a new public API pygame.draw.aaellipse, implements antialiased ellipse/circle rendering in C using Xiaolin Wu variants, updates bindings and stubs, updates an example, and extends tests to cover aaellipse parity with ellipse.

Changes

Cohort / File(s)	Summary
Public stub / API declaration buildconfig/stubs/pygame/draw.pyi	Adds aaellipse(surface: Surface, color: ColorLike, rect: RectLike, width: int = 0) -> Rect declaration (versionadded 2.5.6).
C implementation & bindings src_c/draw.c	Adds aaellipse Python entrypoint and docstring; introduces Xiaolin Wu AA ellipse/circle routines (draw_aaellipse_xiaolinwu, _thin), renames circle Wu paths, adds symmetric-pixel helpers (draw_four_symmetric_pixels, draw_eight_symmetric_pixels, swap_int), updates clipping/bounds and 64-bit-safe arithmetic, routes square rects to aacircle, and registers method in _draw_methods.
Documentation example docs/reST/ref/code_examples/draw_module_example.py	Adjusts example ellipse x positions (+10) and adds two pygame.draw.aaellipse(...) examples (outlined and filled).
Tests test/draw_test.py	Adds draw_aaellipse alias, DrawAAEllipseMixin and DrawAAEllipseTest, and extensive tests mirroring ellipse coverage for aaellipse (args, keywords, color formats, widths, rect formats, bounds, edge/off-screen cases).

Sequence Diagram(s)

sequenceDiagram
  autonumber
  participant App
  participant Draw as pygame.draw
  participant AA as aaellipse()
  participant Clip as Clip/Bounds
  participant Algo as Wu AA Ellipse/Circle
  participant Sym as Symmetric Helpers
  participant Surf as Surface

  App->>Draw: aaellipse(surface, color, rect, width?)
  Draw->>AA: parse args & kwargs

  AA->>Clip: validate rect, compute bounding box, clip
  Clip-->>AA: clipped bounds

  alt rect is square
    AA->>Algo: route to aacircle (thin if width==1)
  else rect is non-square
    AA->>Algo: AA ellipse (thin if width==1)
  end

  Algo->>Sym: compute symmetric pixel positions & coverage
  Sym->>Surf: blend/plot pixels
  Algo-->>AA: return bounding Rect
  AA-->>Draw: Rect
  Draw-->>App: Rect

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

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