// -*-C++-*-

// written by Thorsten Renk, Oct 2015

varying vec4 diffuse_term;
varying vec3 normal;
varying vec3 relPos;


uniform sampler2D texture;
uniform samplerCube cube_texture;

varying float yprime_alt;
varying float mie_angle;


uniform float visibility;
uniform float avisibility;
uniform float scattering;
uniform float terminator;
uniform float terrain_alt; 
uniform float hazeLayerAltitude;
uniform float overcast;
uniform float eye_alt;
uniform float cloud_self_shading;
uniform float angle;
uniform float threshold_low;
uniform float threshold_high;
uniform float emit_intensity;

uniform vec3 offset_vec;
uniform vec3 scale_vec;
uniform vec3 tag_color;
uniform vec3 emit_color;
    

uniform int quality_level;
uniform int tquality_level;
uniform int use_searchlight;
uniform int implicit_lightmap_enabled;


const float EarthRadius = 5800000.0;
const float terminator_width = 200000.0;

float alt;
float eShade;


float fog_func (in float targ, in float alt);
float alt_factor(in float eye_alt, in float vertex_alt);
float light_distance_fading(in float dist);
float fog_backscatter(in float avisibility);

vec3 get_hazeColor(in float light_arg);



float luminance(vec3 color)
{
    return dot(vec3(0.212671, 0.715160, 0.072169), color);
}


float light_func (in float x, in float a, in float b, in float c, in float d, in float e)
{
x = x - 0.5;

// use the asymptotics to shorten computations
if (x > 30.0) {return e;}
if (x < -15.0) {return 0.0;}

return e / pow((1.0 + a * exp(-b * (x-c)) ),(1.0/d));
}

// this determines how light is attenuated in the distance
// physically this should be exp(-arg) but for technical reasons we use a sharper cutoff
// for distance > visibility




void main()
{

  vec3 shadedFogColor = vec3(0.55, 0.67, 0.88);
// this is taken from default.frag
    vec3 n;
    float NdotL, NdotHV, fogFactor;
    vec4 color = gl_Color;
    vec3 lightDir = gl_LightSource[0].position.xyz;
    vec3 halfVector = gl_LightSource[0].halfVector.xyz;
    vec4 texel;
    vec4 fragColor;
    vec4 specular = vec4(0.0);
    float intensity;

    float effective_scattering = min(scattering, cloud_self_shading);

    eShade = 1.0 - 0.9 * smoothstep(-terminator_width+ terminator, terminator_width + terminator, yprime_alt);
    vec4 light_specular = gl_LightSource[0].specular * (eShade - 0.1);

    // If gl_Color.a == 0, this is a back-facing polygon and the
    // normal should be reversed.
    n = (2.0 * gl_Color.a - 1.0) * normal;
    n = normalize(n);

    // lookup on the opacity map
    vec3 light_vec = normalize((gl_ModelViewMatrixInverse * gl_LightSource[0].position).xyz);
    //vec3 light_vec = vec3 (-1.0,0.0,0.0);

    vec4 ep = gl_ModelViewMatrixInverse * vec4(0.0,0.0,0.0,1.0);
    vec3 scaled_pos = relPos + ep.xyz;

    //vec3 lookup_vec = normalize(- normalize(light_vec) + relPos);
    scaled_pos -= offset_vec; 
    float rangle = radians(angle);
    mat2 rotMat = mat2 (cos(rangle), -sin(rangle), sin(rangle), cos(rangle));   
    scaled_pos.xy *=rotMat;

    scaled_pos /= scale_vec;
    
    //vec3 lookup_pos = dot(base1,scaled_pos) * base1 + dot(base2,scaled_pos) * base2;
    vec3 lookup_pos = scaled_pos - light_vec * dot(light_vec, scaled_pos);

    vec3 lookup_vec = normalize(normalize(light_vec) + lookup_pos);
    vec4 opacity = textureCube(cube_texture, lookup_vec);
   

    vec4 diffuse = diffuse_term;
    NdotL = dot(n, lightDir);
    //NdotL = dot(n, (gl_ModelViewMatrix * vec4 (light_vec,0.0)).xyz);
    if (NdotL > 0.0) {

	diffuse.rgb += 2.0 * diffuse.rgb * (1.0 - opacity.a);
        color += diffuse * NdotL * opacity;
        NdotHV = max(dot(n, halfVector), 0.0);
        if (gl_FrontMaterial.shininess > 0.0)
            specular.rgb = (gl_FrontMaterial.specular.rgb
                            * light_specular.rgb
                            * pow(NdotHV, gl_FrontMaterial.shininess));
    }
    color.a = diffuse.a;
    // This shouldn't be necessary, but our lighting becomes very
    // saturated. Clamping the color before modulating by the texture
    // is closer to what the OpenGL fixed function pipeline does.
    //color = clamp(color, 0.0, 1.0);

    

    texel = texture2D(texture, gl_TexCoord[0].st);
    fragColor = color * texel + specular;

   // implicit lightmap - the user gets to select 

   if (implicit_lightmap_enabled == 1)
	{
	float cdiff = (length(texel.rgb - tag_color));
	float enhance = 1.0 - smoothstep(threshold_low, threshold_high, cdiff); 
	fragColor.rgb = fragColor.rgb + enhance * emit_color * emit_intensity;
	}


	

gl_FragColor = fragColor;

}