varying vec3 n, l, h;
varying float i;

#vertex

void main() {
    vec4 pos;

    // normal vector, light direction, half vector
    n = normalize(gl_NormalMatrix * gl_Normal);
    l = normalize(vec3(gl_LightSource[0].position));
    h = normalize(gl_LightSource[0].halfVector.xyz);

    // the rest
    gl_TexCoord[0] = gl_MultiTexCoord0 * 4.0;
    pos = gl_ProjectionMatrix * gl_ModelViewMatrix * gl_Vertex;
    i = 1.0 - 0.1 * pos.z;
    gl_Position = pos;
}

#fragment

uniform sampler2D tex;

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

    // distortion texture lookup
    nn = vec3(texture2D(tex, vec2(3.0 * gl_TexCoord[0].s, 2.0 * gl_TexCoord[0].t)));
    nn -= vec3(0.5, 0.5, 0.5);
    
    // lighting
    nn = normalize(n + 0.3 * nn);
    d = dot(nn, l);
    if (d > 0.0) {
        s = pow(max(dot(nn, normalize(h)), 0.0), 30.0);
        d *= 0.75;
    }
    else {
        s = 0.0;
        d = 0.0;
    }
    
    // color assembly
    nn = vec3(0.150, 0.075, 0.031)       // ambient
       + vec3(0.500, 0.421, 0.200) * d   // diffuse
       + vec3(0.900, 0.900, 0.900) * s;  // specular
    gl_FragColor = i * vec4(nn, 0.0);
}