Question

This is weird, and I can’t find anything like it online. I am rendering a reflective sphere in OpenGL, and I’m trying to reposition the camera and use glCopytexImage2D to render directly to the Cube Map textures. Problem is, my reflective sphere ends up reflecting everything on my desktop EXCEPT the OpenGL environment! How does something like this even happen? It’s tripping me out. I will include my entire renderReflectiveSphere function here:

void drawReflectiveSphere(){

  float sphere_pos[] = {10.0, 0.0, -40.0};

  glMatrixMode(GL_MODELVIEW);
  glDisable(GL_TEXTURE_2D);

  glPushMatrix();
    //Positive x
    gluLookAt(sphere_pos[0], sphere_pos[1], sphere_pos[2],
       sphere_pos[0] + 1, sphere_pos[1], sphere_pos[2],
       0.0, 1.0, 0.0);
    glCopyTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X, 0, GL_RGB, -128, -128, 128, 128, 0);

    //Negative x
    gluLookAt(sphere_pos[0], sphere_pos[1], sphere_pos[2],
       sphere_pos[0] - 1, sphere_pos[1], sphere_pos[2],
       0.0, 1.0, 0.0);
    glCopyTexImage2D(GL_TEXTURE_CUBE_MAP_NEGATIVE_X, 0, GL_RGB, -128, -128, 128, 128, 0);

    //Positive y
    gluLookAt(sphere_pos[0], sphere_pos[1], sphere_pos[2],
       sphere_pos[0], sphere_pos[1] + 1, sphere_pos[2],
       0.0, 0.0, 1.0);
    glCopyTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_Y, 0, GL_RGB, -128, -128, 128, 128, 0);

    //Negative y
    gluLookAt(sphere_pos[0], sphere_pos[1], sphere_pos[2],
       sphere_pos[0], sphere_pos[1] - 1, sphere_pos[2],
       0.0, 0.0, 1.0);
    glCopyTexImage2D(GL_TEXTURE_CUBE_MAP_NEGATIVE_Y, 0, GL_RGB, -128, -128, 128, 128, 0);

    //Positive z
    gluLookAt(sphere_pos[0], sphere_pos[1], sphere_pos[2],
       sphere_pos[0], sphere_pos[1], sphere_pos[2] + 1,
       0.0, 1.0, 0.0);
    glCopyTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_Z, 0, GL_RGB, -128, -128, 128, 128, 0);

    //Negative z
    gluLookAt(sphere_pos[0], sphere_pos[1], sphere_pos[2],
       sphere_pos[0], sphere_pos[1], sphere_pos[2] - 1,
       0.0, 1.0, 0.0);
    glCopyTexImage2D(GL_TEXTURE_CUBE_MAP_NEGATIVE_Z, 0, GL_RGB, -128, -128, 128, 128, 0);
  glPopMatrix();

  glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
  glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
  glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
  glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_REFLECTION_MAP);
  glTexGeni(GL_T, GL_TEXTURE_GEN_MODE, GL_REFLECTION_MAP);
  glTexGeni(GL_R, GL_TEXTURE_GEN_MODE, GL_REFLECTION_MAP);
  glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); 
  glEnable(GL_TEXTURE_GEN_S);
  glEnable(GL_TEXTURE_GEN_T);
  glEnable(GL_TEXTURE_GEN_R);
  glEnable(GL_TEXTURE_CUBE_MAP);

  glPushMatrix();
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(sphere_pos[0], sphere_pos[1], sphere_pos[2]);
    gluSphere(quadratic, 5.0f, 128, 128);
  glPopMatrix();


  //Reset frustrum, etc.
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glFrustum(-1.0, 1.0, -1.0, 1.0, 1.5, depth + 15.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();

  glDisable(GL_TEXTURE_GEN_S);
  glDisable(GL_TEXTURE_GEN_T);
  glDisable(GL_TEXTURE_GEN_R);
  glDisable(GL_TEXTURE_CUBE_MAP);

  glDrawBuffer(GL_BACK);
  glReadBuffer(GL_BACK);
}

I assume I’m doing a few things wrong, but where would OpenGL get the contents of my desktop from? And how can I set myself straight to do what I want?

Answer 1

I eventually solved this but the problem is in code not shown above. Essentially, I initialized my cube map texture to a size much too large.