Python/PyOpenGL: Pipes

Question

I'm trying to learn PyOpenGL, and I understand some of the concept, except the "pipe" "|" character connecting things. For example, this is the code for a cube:

import pygame
from pygame.locals import *

from OpenGL.GL import *
from OpenGL.GLU import *

verticies = (
    (1, -1, -1),
    (1, 1, -1),
    (-1, 1, -1),
    (-1, -1, -1),
    (1, -1, 1),
    (1, 1, 1),
    (-1, -1, 1),
    (-1, 1, 1)
    )

edges = (
    (0,1),
    (0,3),
    (0,4),
    (2,1),
    (2,3),
    (2,7),
    (6,3),
    (6,4),
    (6,7),
    (5,1),
    (5,4),
    (5,7)
    )
def Cube():
    glBegin(GL_LINES)
    for edge in edges:
        for vertex in edge:
            glVertex3fv(verticies[vertex])
    glEnd()


def main():
    pygame.init()
    display = (800,600)
    pygame.display.set_mode(display, DOUBLEBUF|OPENGL)

    gluPerspective(45, (display[0]/display[1]), 0.1, 50.0)

    glTranslatef(0.0,0.0, -5)

    while True:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
                quit()

        glRotatef(1, 3, 1, 1)
        glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
        Cube()
        pygame.display.flip()
        pygame.time.wait(10)
main()

I'm not exactly sure what the GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT thing means, or the DOUBLEBUF|OPENGL

I know what double buffering is, but I still do not fully understand what this or the other thing means.

Answer 1

They are actually just integer constants. This is a convenient way of getting input from user. Pipe operator (|) is a bitwise OR of integers. For example 15 | 128 = 143, i.e. 00001111 | 10000000 = 10001111 in binary.

Here is how it actually works:

>>> from OpenGL.GL import *
>>> type(GL_COLOR_BUFFER_BIT)
OpenGL.constant.IntConstant
>>> int(GL_COLOR_BUFFER_BIT)
16384
>>> bin(GL_COLOR_BUFFER_BIT)
'0b100000000000000'
>>> int(GL_DEPTH_BUFFER_BIT)
256
>>> bin(GL_DEPTH_BUFFER_BIT)
'0b100000000'
>>> int(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
16640
>>> bin(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
'0b100000100000000'