Pygame with OpenGL on RPI Zero without X: invalid operation

[aserranoh]

Hello everyone!

I have the following code, which I just copied from a tutorial on internet (https://www.jarutex.com/index.php/2021/10/15/7164/):

import pygame
from pygame.locals import *
from OpenGL.GL import *
from OpenGL.GLU import *

def render():
    pass

if __name__=="__main__":
    pygame.init()
    fpsClock = pygame.time.Clock()
    pygame.display.set_mode((320,240), pygame.DOUBLEBUF|pygame.OPENGL)
    pygame.display.set_caption("ex01")
    glViewport(0,0,320,240)
    gluOrtho2D(-1.0,1.0,1.0,-1.0)
    running = True
    while running:
        fpsClock.tick(30)
        glClearColor(1.0, 1.0, 1.0, 1.0)
        glClear(GL_COLOR_BUFFER_BIT)
        glMatrixMode(GL_MODELVIEW)
        glLoadIdentity()
        render()
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                running = False
        pygame.display.flip()
    pygame.quit()

When I execute this on the RPI, I get:

Output:
pygame 2.1.2 (SDL 2.0.16, Python 3.9.10)
Hello from the pygame community. https://www.pygame.org/contribute.html
Traceback (most recent call last):
  File "/root/./ex01.py", line 27, in <module>
    glClearColor(1.0, 1.0, 1.0, 1.0)
  File "/usr/lib/python3.9/site-packages/OpenGL/platform/baseplatform.py", line 415, in __call__
    return self( *args, **named )
  File "/usr/lib/python3.9/site-packages/OpenGL/error.py", line 230, in glCheckError
    raise self._errorClass(
OpenGL.error.GLError: GLError(
	err = 1282,
	description = b'invalid operation',
	baseOperation = glClearColor,
	cArguments = (1.0, 1.0, 1.0, 1.0)
)

I have been researching a bit about this and I cannot find the answer. By the way, this code is perfectly fine as it works in my desktop machine with X server though. I'm missing something in the RPI. Maybe the GL_CONTEXT? But if I query the pygame.display.gl_get_attribute() it seems that it gives me some information, as if it would have a GL_CONTEXT. Maybe something related with EGL missing?

Any help would be much appreciated. Thanks!