OpenGL Lighting struggles

Question

I'm in the middle of a project teaching the basics of OpenGL. I've got most of the requirements working fine in terms of camera rotation, translation etc. However I'm struggling a lot with the lighting.

This picture is a comparison of my current program (left) vs the sample solution (right).

In case you can't tell, I'm getting very monochrome colours on the truck. The shadows are very sharp and dark, the high points are singly coloured instead of specular. The project calls for the use of textures; the one I've shown here is a basic texture of plain grey pixels but i could use any texture (including the beach sand one being used for the ground). I'm drawing the object from a mesh:

GLfloat ambient[] = {0.1, 0.1, 0.1, 1};
GLfloat diffuse[] = {0.1, 0.1, 0.1, 1};
GLfloat specular[] = {1.0, 1.0, 1.0, 1.0};
GLfloat shine = 100.0;

glMaterialfv(GL_FRONT, GL_AMBIENT, ambient);
glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuse);
glMaterialfv(GL_FRONT, GL_SPECULAR, specular);
glMaterialf(GL_FRONT, GL_SHININESS, shine);

glEable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, textureNumber);
glBegin(GL_TRIANGLES);

for (int i = 0; i < meshes[n]->nTriangles; i++) {
    for (int j = 0; j < 3; j++) {
        glNormal3fv(mesh -> normals[mesh->triangles[i][j]]);
        glTexCoord2fv(mesh->texCoords[mesh->triangles[i][j]]);
        glVertex3fv(mesh -> vertices[mesh->triangles[i][j]]);
    }
}
glEnd();

There is one light in the scene:

glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glEnable(GL_DEPTH_TEST)


GLfloat diffuse0[]={1.0, 1.0, 1.0, 1.0};
GLfloat ambient0[]={1.0, 1.0, 1.0, 1.0};
GLfloat specular0[]={1.0, 1.0, 1.0, 1.0};
GLfloat light0_pos[]={1.0, 1.0, 1,0, 1.0};

glLightfv(GL_LIGHT0, GL_POSITION, light0_pos);
glLightfv(GL_LIGHT0, GL_AMBIENT, ambient0);
glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuse0);
glLightfv(GL_LIGHT0, GL_SPECULAR, specular0);

glLightf(GL_LIGHT0, GL_CONSTANT_ATTENUATION, 2.0);
glLightf(GL_LIGHT0, GL_LINEAR_ATTENUATION, 1.0);
glLightf(GL_LIGHT0, GL_QUADRATIC_ATTENUATION, 2.0);

Is there something major that I'm missing that could be causing this severe difference? Particular values I should play with? Or a glEnable call I've missed? Any help, advice or pointers to elsewhere much appreciated.

Answer 1

when looking at the background, it looks like a spotlight on the right just bathing the Scene into warm light, and a Flakscheinwerfer on the left basking everything in extreme lightning, eliminating every shadow

Answer 2

To eliminate the sharp drop-off, amp up the ambient light. There's no global illumination model in OpenGL so that parameter has absolutely no effect beyond being the colour the face will be if no other light falls upon it.

Since you're using glVertex-type calls, I'll go out on a limb and guess you're using the fixed functionality pipeline? If so then lighting is calculated at vertices, then interpolated across polygon surfaces. That means that specular highlights don't work very well on 'large' polygons — roughly speaking, the highlight can't appear in the middle of a polygon. GPUs with programmable pipelines (which includes the ones in mobile phones nowadays) can calculate lighting per pixel instead of per vertex but OpenGL doesn't do this for you, so you'd need to delve into shader programming yourself. Or just ensure that your model is made up of small enough polygons.

Your shininess exponent is also quite high - have you tried dialling that down a few notches?