Triangle meshes with Python and pygame

pymesh.py

import pygame
import pygame.freetype
import pygame.gfxdraw


quadrants = (
    (( 0,  0), (+1, -1), (+1, +1)),
    (( 0,  0), (+1, +1), (-1, +1)),
    (( 0,  0), (-1, +1), (-1, -1)),
    (( 0,  0), (-1, -1), (+1, -1)))

octants = (
    ((+1,  0), (+1, +1), ( 0,  0)),
    (( 0, +1), ( 0,  0), (+1, +1)),
    (( 0, +1), (-1, +1), ( 0,  0)),
    ((-1,  0), ( 0,  0), (-1, +1)),
    ((-1,  0), (-1, -1), ( 0,  0)),
    (( 0, -1), ( 0,  0), (-1, -1)),
    (( 0, -1), (+1, -1), ( 0,  0)),
    ((+1,  0), ( 0,  0), (+1, -1)))

def quad0(tri, vert):
    return quadrants[tri][vert]

def octa0(tri, vert):
    return octants[tri][vert]

def test_triangles():
    print('\n'.join('\t'.join('%+d,%+d' % quad0(tri, vert) for vert in range(3)) for tri in range(4)))
    print('\n')
    print('\n'.join('\t'.join('%+d,%+d' % octa0(tri, vert) for vert in range(3)) for tri in range(8)))


def meshmake(lod, x, y):
    triangles = [[((x+1.0)/2.0, (y+1.0)/2.0) for (x, y) in tri] for tri in quadrants[0:3]+octants[7:8]]

    return triangles

def meshdraw(surface, size, mesh):
    black = (0, 0, 0, 0)
    white = (255, 255, 255, 255)
    red = (255, 0, 0, 255)

    def project(size, pos):
        return (
            int(float(size[0]-1) * pos[0]),
            size[1]-int(float(size[1]-1) * pos[1])-1)

    for triangle in mesh:
        v0 = triangle[0]
        v1 = triangle[1]
        v2 = triangle[2]

        x1 = (v1[0] - v0[0])
        y1 = (v1[1] - v0[1])
        x2 = (v2[0] - v0[0])
        y2 = (v2[1] - v0[1])

        cross = x1*y2 - x2*y1

        # back facing = red
        color = white if cross >= 0.0 else red

        for i in range(3):
            b = project(size, triangle[i])
            e = project(size, triangle[(i+1)%3])

            pygame.gfxdraw.line(surface, b[0], b[1], e[0], e[1], color)



if __name__ == '__main__':
    test_triangles()

    pygame.init()
    surface = pygame.display.set_mode((1024,1024)) #, pygame.RESIZABLE)
    size = surface.get_size()
    font = pygame.freetype.Font(None, 18)

    lod = 0
    mouse_pos = (0, 0)

    quit = False
    while not quit:
        event = pygame.event.wait()
        if event.type == pygame.QUIT:
            quit = True
        elif event.type == pygame.MOUSEMOTION:
            mouse_pos = event.pos
        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_PLUS or event.key == pygame.K_KP_PLUS:
                lod = lod + 1
            elif event.key == pygame.K_MINUS or event.key == pygame.K_KP_MINUS:
                lod = max(0, lod - 1)
        elif event.type == pygame.VIDEORESIZE:
            size = event.size

        x = min(int((float(mouse_pos[0]) / float(size[0]))*(1 + (1 << lod))), (1<<lod))
        y = min(int((1.0 - float(mouse_pos[1]) / float(size[1]))*(1 + (1 << lod))), (1<<lod))
        mesh = meshmake(lod, x, y)

        black = (0, 0, 0, 0)
        white = (255, 255, 255, 255)


        surface.fill(black)

        screen_x = size[0] * x / (1 << lod)
        screen_y = size[1] - size[1] * y / (1 << lod)
        surface.fill(white, rect=(screen_x-2, screen_y-2, 5, 5))

        meshdraw(surface, size, mesh)

        status_text = 'lod: %d   mouse_x: %d  mouse_y: %d  x: %d  y: %d  triangles: %d' % (lod, mouse_pos[0], mouse_pos[1], x, y, len(mesh))
        font.render_to(surface, (0, 0), status_text, fgcolor=white)

        pygame.display.flip()

    pygame.display.quit()
    pygame.quit()