Fix issues and inconsistency with draw_line_width

[Temmie3754]

This change resolves issues #1968 and pygame/pygame#3199 through a rewrite of the draw_line_width function. Drawing lines from a to b should now also be the same as drawing from b to a.

[MightyJosip]

It is good now. If you would like to do it, can you also add the tests for this

[MyreMylar]

LGTM 👍

Fixes the original issue that was visible in this test program:

import pygame


WIDTH, HEIGHT = 800, 600
FPS = 60

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

test_surf = pygame.Surface((100, 100))
test_surf.fill((255, 255, 255))

rect = pygame.Rect(0, 0, 100, 100)

test_surf_pos = (150, 150)

running = True
while running:
    clock.tick(FPS)
    screen.fill("black")

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

    test_surf.fill("white")
    rect.center = pygame.mouse.get_pos()[0] - test_surf_pos[0], pygame.mouse.get_pos()[1] - test_surf_pos[0]
    pygame.draw.rect(test_surf, "red", rect, 30, 0, 0, 20, 0, 20)
    screen.blit(test_surf, test_surf_pos)

    pygame.display.flip()

Try moving the D shape around inside the white surface with the mouse. On main you get lots of artefacts when parts of the D are clipped off screen and parts, which should still be visible get culled. After this PR everything looks as it should.

[itzpr3d4t0r]

I tested this and confirm to be faster with this PR:

OLD:
0.3472604100001263
0.34475235999998405
0.3701231299995925
0.33968151999979457
0.3420160299998315
0.34054873000004593
0.3426739000000453
0.3402624100001049
0.35369226999973763
0.34050359000011665

NEW
0.23466548999986117
0.2332005099999151
0.23741479000018445
0.23511996999986878
0.23276994999960152
0.23450463999997737
0.2321502300004795
0.23337097000003268
0.23315945000049396
0.2355904100000771

OLD Mean: 0.34615143499993795
NEW Mean: 0.23419464100004916
Uplift: 47.81%

Code:

from random import randint

import pygame
from pygame.draw import line as draw_line
from timeit import repeat
from statistics import mean

pygame.init()
WIDTH, HEIGHT = 400, 400
win = pygame.display.set_mode((WIDTH, HEIGHT))


def rand_color():
    return randint(0, 255), randint(0, 255), randint(0, 255)


def create_lines(number, width):
    return [(rand_color(),
             (randint(0, WIDTH), randint(0, HEIGHT)),
             (randint(0, WIDTH), randint(0, HEIGHT)), width)
            for _ in range(number)]


lst = create_lines(100, 3)

for _ in range(10):
    print(mean(repeat("for line in lst: draw_line(win, *line)", globals=globals(), number=1000, repeat=10)))