Improve draw performance

[MightyJosip]

Fix #2517

Still need to check what needs clip version, and what doesn't.

[MyreMylar]

Looks like we need to set a default value for set_func here to please gcc. I guess something like:

Suggested change

	int (*set_func)(SDL_Surface*, int, int, Uint32);
	int (*set_func)(SDL_Surface*, int, int, Uint32) = &set_at_32bit_clip;

[MyreMylar]

One thing I'm slightly concerned about using this approach is that C function pointers and performance intensive tight loops are classically not always the best of friends, though this is somewhat compiler dependant.

As a test, I've tried swapping out the function pointer call in set_and_check_rect() for a clone of the function it is calling:

static int
set_at_32bit_no_func_pointer(SDL_Surface *surf, int x, int y, Uint32 color)
{
    if (x < surf->clip_rect.x || x >= surf->clip_rect.x + surf->clip_rect.w ||
        y < surf->clip_rect.y || y >= surf->clip_rect.y + surf->clip_rect.h)
    {
        return 0;
    }

    *((Uint32 *)((Uint8 *)surf->pixels + y * surf->pitch) + x) = color;
    return 1;
}

static void
set_and_check_rect(SDL_Surface *surf, int x, int y, Uint32 color,
                   int *drawn_area, int (*set_func)(SDL_Surface*, int, int, Uint32))
{
    if (set_at_32bit_no_func_pointer(surf, x, y, color))
        add_pixel_to_drawn_list(x, y, drawn_area);
}

And on my PC the version without the function pointer was running 15-30% faster in my simple line drawing performance test:

from sys import stdout
from pstats import Stats
from cProfile import Profile


import pygame

pygame.init()


def draw_line_short_inside():
    lines = [
        ((256, 256), (0, 0)),
        ((128, 256), (160, 0)),
        ((50, 256), (128, 0)),
        ((0, 240), (12, 56)),
        ((50, 40), (60, 11)),
    ]
    widths = [1]
    surf = pygame.Surface((256, 256), pygame.SRCALPHA, 32)
    surf.fill((255, 255, 255, 255))
    for iterations in range(0, 10000):
        for line in lines:
            for width in widths:
                pygame.draw.line(
                    surf, pygame.Color("red"), line[0], line[1], width=width
                )


def draw_line_long_inside():
    lines = [
        ((1256, 256), (0, 0)),
        ((1128, 256), (128, 0)),
        ((150, 1256), (128, 0)),
        ((0, 240), (1200, 56)),
        ((50, 40), (1060, 11)),
    ]
    widths = [1]
    surf = pygame.Surface((2048, 2048), pygame.SRCALPHA, 32)
    surf.fill((255, 255, 255, 255))
    for iterations in range(0, 10000):
        for line in lines:
            for width in widths:
                pygame.draw.line(
                    surf, pygame.Color("red"), line[0], line[1], width=width
                )


def draw_line_short_outside():
    lines = [
        ((256, 256), (0, 0)),
        ((128, 256), (160, 0)),
        ((50, 256), (128, 0)),
        ((0, 240), (12, 56)),
        ((50, 40), (80, 11)),
    ]
    widths = [1]
    surf = pygame.Surface((64, 64), pygame.SRCALPHA, 32)
    surf.fill((255, 255, 255, 255))
    for iterations in range(0, 10000):
        for line in lines:
            for width in widths:
                pygame.draw.line(
                    surf, pygame.Color("red"), line[0], line[1], width=width
                )


def draw_line_long_outside():
    lines = [
        ((2256, 256), (0, 0)),
        ((2128, 256), (128, 0)),
        ((150, 4256), (128, 0)),
        ((0, 240), (2200, 56)),
        ((50, 40), (4060, 11)),
    ]
    widths = [1]
    surf = pygame.Surface((1024, 1024), pygame.SRCALPHA, 32)
    surf.fill((255, 255, 255, 255))
    for iterations in range(0, 10000):
        for line in lines:
            for width in widths:
                pygame.draw.line(
                    surf, pygame.Color("red"), line[0], line[1], width=width
                )


if __name__ == "__main__":
    print("Draw Line - short, inside surface")
    profiler = Profile()
    profiler.runcall(draw_line_short_inside)
    stats = Stats(profiler, stream=stdout)
    stats.strip_dirs()
    stats.sort_stats("cumulative")
    stats.print_stats()

    print("\nDraw Line - long, inside surface")
    profiler = Profile()
    profiler.runcall(draw_line_long_inside)
    stats = Stats(profiler, stream=stdout)
    stats.strip_dirs()
    stats.sort_stats("cumulative")
    stats.print_stats()

    print("\nDraw Line - short, edges outside surface")
    profiler = Profile()
    profiler.runcall(draw_line_short_outside)
    stats = Stats(profiler, stream=stdout)
    stats.strip_dirs()
    stats.sort_stats("cumulative")
    stats.print_stats()

    print("\nDraw Line - long, edges a long way outside surface")
    profiler = Profile()
    profiler.runcall(draw_line_long_outside)
    stats = Stats(profiler, stream=stdout)
    stats.strip_dirs()
    stats.sort_stats("cumulative")
    stats.print_stats()

I'd be curious if you see similar results.

[MightyJosip]

Closed in favor of #2551