Question

I am currently trying to get into OpenGL shading and lighting to display a 3D model exported from Blender in a simple GLUT window.

I tried to display the typical glutSolidTeapot to validate my OpenGL settings.
With the Teapot everything looks perfectly fine as can be seen in the pic below.

If I now want to replace the teapot with my own Blender-exported model, the shading doesn’t work. The model ( a car rim ) just looks solid-colored.
The color changes when the model is rotated, but it stays solid all the time.

What does glutSolidTeapot do under the hood to draw the teapot model?

Here’s the code I’m using to set up OpenGL :

void SetupRC()
{
    glClearColor(0.4, 0.4, 0.4, 1.0);

    // Enable lighting and the light we have set up
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);

    //Set lighting parameters
    glLightfv(GL_LIGHT0,GL_POSITION,light_position);
    glLightfv(GL_LIGHT0, GL_AMBIENT,light_ambient);
    glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);
    glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);

    glEnable(GL_COLOR_MATERIAL);
    glColorMaterial(GL_FRONT_AND_BACK,GL_DIFFUSE);

    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    // Enable shading
    glShadeModel(GL_SMOOTH);

    // Set up the projection parameters
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    glFrustum(-1.0, 1.0, -1.0, 1.0, 2.0, 20.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glEnable(GL_AUTO_NORMAL);
    glEnable(GL_NORMALIZE);
}

And the code to repaint the frames :

void RenderScene(void)
{
    glLoadIdentity();
    glMatrixMode(GL_MODELVIEW);

    glTranslatef(0.0, 0.0, -2.5f);

    glRotatef(xRot, 1.0f, 0.0f, 0.0f);
    glRotatef(yRot, 0.0f, 1.0f, 0.0f);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // set input data to arrays
    glVertexPointer(3, GL_FLOAT, 0, BlenderGuru_CarWheelVerts);

    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

    GLfloat ambConst[] = { 0.24725, 0.1995, 0.0745, 1.0};
    glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, ambConst);

    GLfloat diffConst[] = { 0.75164, 0.60648, 0.22648, 1.0 };
    glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, diffConst);

    GLfloat specConst[] = { 0.628281, 0.555802, 0.366065, 1.0 };
    glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, specConst);

    glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 51.2);

    // draw data
    glEnableClientState(GL_VERTEX_ARRAY);
        glDrawArrays(GL_TRIANGLES, 0, BlenderGuru_CarWheelNumVerts);
    glDisableClientState(GL_VERTEX_ARRAY);

    glFlush();
}

Answer 1

Since you are exporting from Blender, your exported data will most likely also contain normals. If not, make sure you generate them for your model and export them. You need normal data for your lighting to work.

The call to glEnable(GL_AUTO_NORMAL); does not do what you might think it does. It will only

generate normal vectors when either GL_MAP2_VERTEX_3 or GL_MAP2_VERTEX_4 is used to generate vertices.

So export normal data yourself and use this, or perhaps calculate the normals from the mesh data that is available to you.