gldrawpixels on pyopengl not drawing anything?

Question

I create pixels buffer to be drawn with glDrawPixels. The code run ok and the pygame window shows up. But nothing to be drawn, only a blank white window shown. Even if I change the value of buffer, it doesn't draw anything.

import pygame

from OpenGL.GL import *

#initiliaze pixel buffers
buffer = bytearray(800 * 600 * 3)

for i in range(800 * 600 * 3):
    buffer[i] = 25

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

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

        glClear(GL_COLOR_BUFFER_BIT)
        glDrawPixels(800, 600, GL_RGB, GL_UNSIGNED_BYTE, buffer)
        pygame.time.wait(10)

main()

any help?

Answer 1

You missed to update the display by pygame.display.flip(). When the display is an OPENGL display then this will perform a buffer swap:

import pygame
from OpenGL.GL import *
windowsize = (800,600)

# create 800x600 buffer with RED color
buffer = bytearray(windowsize[0] * windowsize[1] * 3)
for i in range(windowsize[0] * windowsize[1]):
    buffer[i*3] = 255
    buffer[i*3+1] = 0
    buffer[i*3+2] = 0

def main():
    pygame.init()

    # create `OPENGL`, `DOUBLEBUF` display
    pygame.display.set_mode(windowsize, pygame.DOUBLEBUF| pygame.OPENGL)

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

        # set BLACK clear color and clear the color plane
        glClearColor(0, 0, 0, 1)
        glClear(GL_COLOR_BUFFER_BIT)

        # draw buffer to dispaly
        glDrawPixels(*windowsize, GL_RGB, GL_UNSIGNED_BYTE, buffer)

        # update display
        pygame.display.flip() # <----- swap buffers

        pygame.time.wait(10)

main()