#version 110

#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(0.6985074, 0.1397015, 0.6985074);
#define LIGHT_FRONT_DIFFUSE  (0.3 * INTENSITY_CORRECTION)

#define INTENSITY_AMBIENT    0.3

// vertex attributes
in vec3 v_position;
in vec3 v_normal;
// instance attributes
in vec3 i_offset;
in vec2 i_scales;

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

void main()
{
    // First transform the normal into camera space and normalize the result.
    vec3 eye_normal = normalize(gl_NormalMatrix * v_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(eye_normal, LIGHT_TOP_DIR), 0.0);

    intensity.x = INTENSITY_AMBIENT + NdotL * LIGHT_TOP_DIFFUSE;
    vec4 world_position = vec4(v_position * vec3(vec2(i_scales.x), i_scales.y) + i_offset, 1.0);
    vec3 eye_position = (gl_ModelViewMatrix * world_position).xyz;
    intensity.y = LIGHT_TOP_SPECULAR * pow(max(dot(-normalize(eye_position), reflect(-LIGHT_TOP_DIR, eye_normal)), 0.0), LIGHT_TOP_SHININESS);

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

    gl_Position = gl_ProjectionMatrix * vec4(eye_position, 1.0);
}