PyOpenGL 3.1.0 with Pygame

Question

I'm learning the OpenGL library with Python, so I use PyOpenGL 3.1.0 with Python 3.6.4 (and pygame 1.9.4 for windowing)

I watched some videos to learn how to render basic triangles with VBOs and VAOs, and so I writed the following code, but I don't understand why my code does not render a simple rectangle from the vertices array...

I think that I missed something about array attribution in vbo but I'm not sure.. Anyone ?

import pygame,numpy
from OpenGL.GL import *
from OpenGL.GLU import *


display = (800,600)

#pygame

pygame.init()
pygame.display.set_mode(display,pygame.DOUBLEBUF|pygame.OPENGL)

#opengl
"""
glMatrixMode(GL_PROJECTION)
gluPerspective(45, (display[0]/display[1]), 0.1, 4000)"""

vertices = [-0.5,0.5,0,
            -0.5,-0.5,0,
            0.5,-0.5,0,

            0.5,-0.5,0,
            0.5,0.5,0,
            -0.5,0.5,0]

vertices = numpy.array(vertices,dtype=numpy.float32)


vao = GLuint()
glGenVertexArrays(1,vao)
glBindVertexArray(vao)

vbo = GLuint()
glGenBuffers(1,vbo)
glBindBuffer(GL_ARRAY_BUFFER,vbo)

glBufferData(GL_ARRAY_BUFFER,len(vertices)*4,vertices,GL_STATIC_DRAW)
glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,0,0)

glBindBuffer(GL_ARRAY_BUFFER,0)
glBindVertexArray(0)

a=1

while a:

    for event in pygame.event.get():

        if event.type == pygame.QUIT:
            a = 0

    glClearColor(0, 0, 1, 0)
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT )

    glBindVertexArray(vao)
    glEnableVertexAttribArray(0)
    glDrawArrays(GL_TRIANGLES,0,len(vertices)//3)
    glDisableVertexAttribArray(0)
    glBindVertexArray(0)

    pygame.display.flip()
    pygame.time.wait(10)

pygame.quit()

Answer 1

The issue is the call to glVertexAttribPointer.

If a named array buffer object is bound then the last parameter (6th parameter) is treated as a byte offset into the buffer object's data store. The data type of the parameter has to be ctypes.c_void_p.

This means you have to use a ctypes.cast:

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, ctypes.cast(0, ctypes.c_void_p))

or None:

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, None)

---

Thoes days it is common to use a shader program.
If you don't use a shader program, then yuo have to use fixed function attributes (glEnableClientState, glVertexPointer ...).
The only exception is vertex attribute 0. Setting the vertex attribute 0 is completely equivalent to setting the fixed function vertex coordinate array (glVertexPointer).
See also What are the Attribute locations for fixed function pipeline in OpenGL 4.0++ core profile?.