// Phong shading with two lights
// WARNING: squares the result color!

varying vec3 n, l0, h0, l1, h1;

#vertex

void main() {
    // normal vector, light direction, half vector
    n = normalize(gl_NormalMatrix * gl_Normal);
    l0 = normalize(vec3(gl_LightSource[0].position) - vec3(gl_ModelViewMatrix * gl_Vertex));
    h0 = normalize(gl_LightSource[0].halfVector.xyz);
    l1 = normalize(vec3(gl_LightSource[1].position) - vec3(gl_ModelViewMatrix * gl_Vertex));
    h1 = normalize(gl_LightSource[1].halfVector.xyz);

    // the rest
    gl_FrontColor = gl_Color;
    gl_Position = ftransform();
}

#fragment

void main() {
    float d;
    vec3 nn;
    vec4 col = gl_Color * gl_LightModel.ambient;

    // lighting
    nn = normalize(n);
    d = dot(nn, normalize(l0));
    if (d > 0.0) {
        col += gl_Color * d;
        col += gl_FrontMaterial.specular * pow(max(dot(nn, normalize(h0)), 0.000001), gl_FrontMaterial.shininess);
    }
    d = dot(nn, normalize(l1));
    if (d > 0.0) {
        col += gl_Color * d;
        col += gl_FrontMaterial.specular * pow(max(dot(nn, normalize(h1)), 0.000001), gl_FrontMaterial.shininess);
    }
    gl_FragColor = col * col;
}