#version 110

#define INTENSITY_AMBIENT    0.3
#define INTENSITY_CORRECTION 0.6

// normalized values for (-0.6/1.31, 0.6/1.31, 1./1.31)
const vec3 LIGHT_TOP_DIR = vec3(-0.4574957, 0.4574957, 0.7624929);
#define LIGHT_TOP_DIFFUSE    (0.8 * INTENSITY_CORRECTION)
#define LIGHT_TOP_SPECULAR   (0.125 * INTENSITY_CORRECTION)
#define LIGHT_TOP_SHININESS  20.0

// normalized values for (1./1.43, 0.2/1.43, 1./1.43)
const vec3 LIGHT_FRONT_DIR = vec3(0.0, 0.0, 1.0);
#define LIGHT_FRONT_DIFFUSE  (0.3 * INTENSITY_CORRECTION)

uniform vec4 uniform_color;

varying vec3 eye_position;
varying vec3 eye_normal;
//varying float world_normal_z;

// x = tainted, y = specular;
vec2 intensity;

void main()
{
    vec3 normal = normalize(eye_normal);

    // Compute the cos of the angle between the normal and lights direction. The light is directional so the direction is constant for every vertex.
    // Since these two are normalized the cosine is the dot product. We also need to clamp the result to the [0,1] range.
    float NdotL = max(dot(normal, LIGHT_TOP_DIR), 0.0);

    intensity.x = INTENSITY_AMBIENT + NdotL * LIGHT_TOP_DIFFUSE;
    intensity.y = LIGHT_TOP_SPECULAR * pow(max(dot(-normalize(eye_position), reflect(-LIGHT_TOP_DIR, normal)), 0.0), LIGHT_TOP_SHININESS);

    // Perform the same lighting calculation for the 2nd light source (no specular applied).
    NdotL = max(dot(normal, LIGHT_FRONT_DIR), 0.0);
    intensity.x += NdotL * LIGHT_FRONT_DIFFUSE;    

//    // darkens fragments whose normal points downward
//    if (world_normal_z < 0.0)
//        intensity.x *= (1.0 + world_normal_z * (1.0 - INTENSITY_AMBIENT));

    gl_FragColor = vec4(vec3(intensity.y, intensity.y, intensity.y) + uniform_color.rgb * intensity.x, uniform_color.a);
}