varying vec3 n, l, h;

#vertex

void main() {
    n = normalize(gl_NormalMatrix * gl_Normal);
    l = normalize(vec3(gl_LightSource[0].position) - vec3(gl_ModelViewMatrix * gl_Vertex));
    h = normalize(gl_LightSource[0].halfVector.xyz);
    gl_TexCoord[0] = vec4(gl_Vertex.x + gl_Vertex.z, gl_Vertex.y - gl_Vertex.z, 0.0, 0.0);
    gl_Position = ftransform();
}

#fragment

uniform sampler2D tex;
uniform float a;

void main() {
    float d, s;
    vec3 nn;

    // distortion texture lookup
    nn = vec3(texture2D(tex, vec2(gl_TexCoord[0])));
    nn -= vec3(0.5, 0.5, 0.5);
    
    // lighting
    nn = normalize(n + 0.25 * nn);
    d = dot(nn, normalize(l));
    if (d > 0.0) {
        s = pow(max(dot(nn, normalize(h)), 0.0), 100.0);
    }
    else {
        s = 0.0;
        d = 0.0;
    }
    
    // color assembly    
    nn = vec3(1.0, 1.0, 1.0) * d;
       + vec3(3.0, 3.0, 3.0) * s;
    gl_FragColor = vec4(nn, a);
}