void main()
{
    vec4 P = gl_ModelViewMatrix*gl_Vertex;
    vec4 E = gl_ProjectionMatrixInverse*vec4(0,0,-1,0);
    vec3 V = normalize(E.xyz*P.w-P.xyz*E.w);
    vec3 N = normalize(gl_NormalMatrix*gl_Normal);

    /* accumulate light contribution */
    gl_FrontColor = vec4(0);
    for(int i=0; i<gl_MaxLights; i++) {
	vec3 L = normalize(gl_LightSource[i].position.xyz*P.w
			   - P.xyz*gl_LightSource[i].position.w);
	vec3 H = normalize(L+V);
        float diff = dot(N,L);

	gl_FrontColor += gl_LightSource[i].ambient;
	if (diff > 0.) {
	    gl_FrontColor += gl_LightSource[i].diffuse * diff;
	    gl_FrontColor += gl_LightSource[i].specular *
		max(pow(dot(N,H),gl_FrontMaterial.shininess),0.);
	}
    }

    gl_TexCoord[0] = gl_TextureMatrix[0]*gl_MultiTexCoord0;
    gl_Position = ftransform();
}