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smelvin

How and when to use glMaterial?

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Hi Sorry if this has been done before, but I can''t get my head round when I can use glMaterial. I have calls to glMaterial just before my objects vertices are drawn. Great! I can see the object no problem, but I don''t get any lighting effects. Yes lighting is enabled and setup (I used an example from online Red Book). Is there something else that needs to be enabled? Any tips/advice would be most welcome.

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Enabling lighting isn''t sufficient. You also need to define
the normals for your surfaces.
Without them you won''t see any lighting in your scene.

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I am loading an OBJ file that has the normals defined. and in my rendering code I am also making the call to glNormal along with glTexCoord etc. Here is an extract


  
if(ptrTIndex != NULL) glBindTexture(GL_TEXTURE_2D, GLtextures[texture_id]);
glMaterialfv(GL_FRONT,GL_DIFFUSE,diffuse);
glMaterialfv(GL_FRONT,GL_AMBIENT,ambient);
glMaterialfv(GL_FRONT,GL_SPECULAR,specular);

glBegin(GL_TRIANGLES);
if (ptrNIndex != NULL)
{
while(nVertexCount--)
{
glNormal3fv(m_pNormals[ptrNIndex++->nVertex].vertex);
glTexCoord2fv(m_pTexcoords[ptrTIndex++->nVertex].tex);
glVertex3fv(m_pVertices[ptrVIndex++->nVertex].vertex);
}
}


The lighting is set up as follows:-

  
GLfloat Ka[] = {0.5000f, 0.5000f, 0.5000f, 1.0f};
GLfloat Kd[] = {0.7000f, 0.7000f, 0.7000f, 1.0f};
GLfloat Ks[] = {1.0000f, 1.0000f, 1.0000f, 1.0f};
GLfloat lightpos[] = { 0.30f, 3.0f, 1.0f, 0.0f };

glLightfv(GL_LIGHT1, GL_AMBIENT, Ka);
glLightfv(GL_LIGHT1, GL_DIFFUSE, Kd);
glLightfv(GL_LIGHT1, GL_POSITION, lightpos);

glEnable(GL_LIGHTING);
glEnable(GL_LIGHT1);
glEnable(GL_TEXTURE_2D);


I thought that this would be enough. I mean I can see the object, no problem. Its just when I rotate it I do not see any light effects as it rotates.

Thanks in advance.

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You need to be carefull when to setup your lights since lights in OpenGL are affected by modelview transformations. So when you rotate your object and the light follows you won''t see any lighting effects...

Hope this helps!

ALex

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