Why my texture is not showing PyOpenGL

Question

I tried everything but still I don't get my error. I am trying to put a texture on my sphere object.

"""
Minimal texture on sphere demo
This is demo for showing how to put image
on sphere as texture in PyOpenGL.
"""
from OpenGL.GLUT import *
from OpenGL.GLU import *
from OpenGL.GL import *
from PIL import Image
import numpy


def run_scene():
    glutInit()
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH)
    glutCreateWindow("Minimal sphere OpenGL")
    lightning()
    glutDisplayFunc(draw_sphere)
    glMatrixMode(GL_PROJECTION)
    gluPerspective(40, 1, 1, 40)
    glMatrixMode(GL_MODELVIEW)
    gluLookAt(0, 0, 10,
              0, 0, 0,
              0, 1, 0)
    glPushMatrix()
    glutMainLoop()
    return


def lightning():
    glEnable(GL_DEPTH_TEST)
    glEnable(GL_LIGHTING)
    glEnable(GL_BLEND)
    glLightfv(GL_LIGHT0, GL_POSITION, [10, 4, 10, 1])
    glLightfv(GL_LIGHT0, GL_DIFFUSE, [0.8, 1, 0.8, 1])
    glLightf(GL_LIGHT0, GL_CONSTANT_ATTENUATION, 0.1)
    glLightf(GL_LIGHT0, GL_LINEAR_ATTENUATION, 0.05)
    glEnable(GL_LIGHT0)
    return


def draw_sphere():
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
    glPushMatrix()
    texture_id = read_texture('mars.png')
    glEnable(GL_TEXTURE_2D)
    glBindTexture(GL_TEXTURE_2D, texture_id)
    glEnable(GL_TEXTURE_GEN_S)
    glEnable(GL_TEXTURE_GEN_T)
    glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_SPHERE_MAP)
    glTexGeni(GL_T, GL_TEXTURE_GEN_MODE, GL_SPHERE_MAP)
    glutSolidSphere(1, 50, 50)
    glDisable(GL_TEXTURE_2D)
    glPopMatrix()
    glutSwapBuffers()
    return


def read_texture(filename):
    img = Image.open(filename)
    img_data = numpy.array(list(img.getdata()), numpy.int8)
    texture_id = glGenTextures(1)
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL)
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, img.size[0], img.size[1], 0,
                 GL_RGB, GL_UNSIGNED_BYTE, img_data)
    return texture_id


if __name__ == '__main__':
    run_scene()

This is result of this code, simple green sphere as this:

But this is not my expected result. I want to simply show this texture mars.png on sphere surface:

Help me with this I cannot solve this on my own it seems.

Answer 1

In read_texture() after you generate a texture name you don't bind it. So the subsequent texture related calls are going to the default texture and not your newly created texture.

texture_id = glGenTextures(1)
glBindTexture(GL_TEXTURE_2D, texture_id) # This is what's missing

Also since your image is a PNG image. Then list(img.getdata()) will be a list of tuples containing (R, G, B, A). So when calling glTexImage2D you need to tell that your data is GL_RGBA and not GL_RGB.

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, img.size[0], img.size[1], 0,
             GL_RGBA, GL_UNSIGNED_BYTE, img_data)

You can also automate it.

format = GL_RGB if img.mode == "RGB" else GL_RGBA
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, img.size[0], img.size[1], 0,
             format, GL_UNSIGNED_BYTE, img_data)

You can also convert it to not have an alpha channel.

img = img.convert("RGB")

Which of course needs to be done before calling img.getdata().

Now you should see the following:

Also an important note. You're calling read_texture() in draw_sphere(). This means that every time draw_sphere() is called, the image is loaded and a new texture is created. You really don't want to do that. Instead before calling glutMainLoop() call read_texture() and store the result as a global name.