thick_aaline.py

import pygame as pg
import math
from pygame.locals import *

"""
thick_aaline(surface, color, point0, point1, width)
  draw a anti-aliased line from point1 to point2 with given width
  
  The algorithms computes the corners (a, b, c, and d)
  that form the borders of the thick line and then draws a filled
  polygon to accomplish that:
  
                 
  B-----------------------------------------C    --+
  0                 line to                 1      | W
  A-----------------------------------------B    --+
  
  Based the the fact that the delta x and y of the line are 
  a fixed proportion  of the delta x and y of the end lines AB CB
  
  -- by Gerry Jenkins
  youtube channel: www.youtube.com/user/gjenkinslbcc 
  
"""

pg.init()
screen = pg.display.set_mode((500, 500))
pg.display.set_caption("aaline with width")
screen.fill(pg.Color('white'))  # black background

# line from p0 to p1 with width w
def thick_aaline(display, color, point0, point1, w):
    x0, y0 = point0
    x1, y1 = point1
    proportion = w / math.hypot(x1 - x0, y1 - y0) / 2
    adjx = (x1 - x0) * proportion  # x side
    adjy = (y1 - y0) * proportion  # y side

    pts = ((x0 - adjy, y0 + adjx),  # A
           (x0 + adjy, y0 - adjx),  # B
           (x1 + adjy, y1 - adjx),  # C
           (x1 - adjy, y1 + adjx))  # D

    pg.draw.aalines(display, color, True, pts, True)  # outline
    pg.draw.polygon(display, color, pts, 0)  # fill it


# test it out
p0 = (50, 100)
p1 = (400, 200)
thick_aaline( screen, pg.Color('blue'), p0, p1, 5)

pg.display.update()

done = False
while not done:
    for e in pg.event.get():
        if e.type == pg.QUIT:
            done = True
        if e.type == KEYDOWN:
            if e.key in (K_ESCAPE, K_SYSREQ):
                done = True