// -*-C++-*-
//  © Vivian Meazza - 2011
// adapted to Atmospheric Light Scattering by Thorsten Renk 2013

// Shader that uses OpenGL state values to do per-pixel lighting
//
// The only light used is gl_LightSource[0], which is assumed to be
// directional.
//
// Diffuse colors come from the gl_Color, ambient from the material. This is
// equivalent to osg::Material::DIFFUSE.

#version 120
#define fps2kts 0.5925

#define MODE_OFF 0
#define MODE_DIFFUSE 1
#define MODE_AMBIENT_AND_DIFFUSE 2

// The ambient term of the lighting equation that doesn't depend on
// the surface normal is passed in gl_{Front,Back}Color. The alpha
// component is set to 1 for front, 0 for back in order to work around
// bugs with gl_FrontFacing in the fragment shader.
varying vec4 diffuse_term;
varying vec3 normal;
varying vec3 relPos;

varying float yprime_alt;
varying float mie_angle;


uniform int colorMode;
uniform float osg_SimulationTime;
uniform float Offset, AmpFactor, WindE, WindN, spd, hdg;
uniform sampler3D Noise;
uniform float hazeLayerAltitude;
uniform float terminator;
uniform float terrain_alt; 
uniform float avisibility;
uniform float visibility;
uniform float overcast;
uniform float ground_scattering;
uniform float moonlight;

// This is the value used in the skydome scattering shader - use the same here for consistency?
const float EarthRadius = 5800000.0;
const float terminator_width = 200000.0;

float earthShade;

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 < -15.0) {return 0.0;}

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

float normalize_range(float _val)
    {
    if (_val > 180.0)
        return _val - 360.0;
    else
        return _val;
    }

void relWind(out float rel_wind_speed_kts, out float rel_wind_from_rad)
    {
    //calculate speed north and east in kts
    float speed_north_kts = cos(radians(hdg)) * spd ;
    float speed_east_kts  = sin(radians(hdg)) * spd ;

    //calculate the relative wind speed north and east in kts
    float rel_wind_speed_from_east_kts = WindE*fps2kts + speed_east_kts;
    float rel_wind_speed_from_north_kts = WindN*fps2kts + speed_north_kts;

    //combine relative speeds north and east to get relative windspeed in kts
    rel_wind_speed_kts = sqrt(pow(abs(rel_wind_speed_from_east_kts), 2.0)
        + pow(abs(rel_wind_speed_from_north_kts), 2.0));

    //calculate the relative wind direction
    float rel_wind_from_deg = degrees(atan(rel_wind_speed_from_east_kts, rel_wind_speed_from_north_kts));
    //rel_wind_from_rad = atan(rel_wind_speed_from_east_kts, rel_wind_speed_from_north_kts);
    float rel_wind = rel_wind_from_deg - hdg;
    rel_wind = normalize_range(rel_wind);
    rel_wind_from_rad = radians(rel_wind);
    }

void rotationmatrix(in float angle, out mat4 rotmat)
    {
    rotmat = mat4( cos( angle ), -sin( angle ), 0.0, 0.0,
        sin( angle ),  cos( angle ), 0.0, 0.0,
        0.0         ,  0.0         , 1.0, 0.0,
        0.0         ,  0.0         , 0.0, 1.0 );
    }

void main()
    {
	vec4 light_diffuse;
    vec4 light_ambient;
    vec3 shadedFogColor = vec3(0.65, 0.67, 0.78);
    vec3 moonLightColor = vec3 (0.095, 0.095, 0.15) * moonlight;


    float yprime;
    float lightArg;
    float intensity;
    float vertex_alt;
    float scattering;
	
	
	
    mat4 RotationMatrix;

    float relWindspd=0.0;
    float relWinddir=0.0;

    // compute relative wind speed and direction
    relWind (relWindspd, relWinddir);

    // map noise vector
    vec4 noisevec = texture3D(Noise, gl_Vertex.xyz);

    //waving effect
    float tsec = osg_SimulationTime;
    vec4 pos = gl_Vertex;
    vec4 oldpos = gl_Vertex;

    float freq = (10.0 * relWindspd) + 10.0;
    pos.y = sin((pos.x * 5.0 + tsec * freq )/5.0) * 0.5 ;
    pos.y += sin((pos.z * 5.0 + tsec * freq/2.0)/5.0) * 0.125 ;

    pos.y *= pow(pos.x - Offset, 2.0) * AmpFactor;

    //rotate the flag to align with relative wind
    rotationmatrix(-relWinddir, RotationMatrix);
    pos *= RotationMatrix;
    gl_Position = gl_ModelViewProjectionMatrix * pos;

    //do the colour and fog
    vec4 ecPosition = gl_ModelViewMatrix * gl_Vertex;


    gl_TexCoord[0] = gl_TextureMatrix[0] * gl_MultiTexCoord0;
    normal = gl_NormalMatrix * gl_Normal;
    vec4 ambient_color, diffuse_color;

    if (colorMode == MODE_DIFFUSE) {
        diffuse_color = gl_Color;
        ambient_color = gl_FrontMaterial.ambient;
        } else if (colorMode == MODE_AMBIENT_AND_DIFFUSE) {
            diffuse_color = gl_Color;
            ambient_color = gl_Color;
        } else {
            diffuse_color = gl_FrontMaterial.diffuse;
            ambient_color = gl_FrontMaterial.ambient;
            }

			
	// first current altitude of eye position in model space
    vec4 ep = gl_ModelViewMatrixInverse * vec4(0.0,0.0,0.0,1.0);
    
    // and relative position to vector
    relPos = gl_Vertex.xyz - ep.xyz;

    // unfortunately, we need the distance in the vertex shader, although the more accurate version
    // is later computed in the fragment shader again
    float dist = length(relPos);

    // altitude of the vertex in question, somehow zero leads to artefacts, so ensure it is at least 100m
    vertex_alt = max(gl_Vertex.z,100.0);
    scattering = ground_scattering + (1.0 - ground_scattering) * smoothstep(hazeLayerAltitude -100.0, hazeLayerAltitude + 100.0, vertex_alt); 


    // branch dependent on daytime

if (terminator < 1000000.0) // the full, sunrise and sunset computation
{
    

    // establish coordinates relative to sun position

    vec3 lightFull = (gl_ModelViewMatrixInverse * gl_LightSource[0].position).xyz;
    vec3 lightHorizon = normalize(vec3(lightFull.x,lightFull.y, 0.0));
  

    
    // yprime is the distance of the vertex into sun direction
    yprime = -dot(relPos, lightHorizon);

    // this gets an altitude correction, higher terrain gets to see the sun earlier
    yprime_alt = yprime - sqrt(2.0 * EarthRadius * vertex_alt);

    // two times terminator width governs how quickly light fades into shadow
    // now the light-dimming factor
    earthShade = 0.6 * (1.0 - smoothstep(-terminator_width+ terminator, terminator_width + terminator, yprime_alt)) + 0.4;
  
   // parametrized version of the Flightgear ground lighting function
    lightArg = (terminator-yprime_alt)/100000.0;

    // directional scattering for low sun
    if (lightArg < 10.0)
    	{mie_angle = (0.5 *  dot(normalize(relPos), normalize(lightFull)) ) + 0.5;}
    else 
	{mie_angle = 1.0;}




   light_diffuse.b = light_func(lightArg, 1.330e-05, 0.264, 3.827, 1.08e-05, 1.0);
   light_diffuse.g = light_func(lightArg, 3.931e-06, 0.264, 3.827, 7.93e-06, 1.0);
   light_diffuse.r = light_func(lightArg, 8.305e-06, 0.161, 3.827, 3.04e-05, 1.0);
   light_diffuse.a = 1.0;
   light_diffuse = light_diffuse * scattering;


   light_ambient.r = light_func(lightArg, 0.236, 0.253, 1.073, 0.572, 0.33);
   light_ambient.g = light_ambient.r * 0.4/0.33; 
   light_ambient.b = light_ambient.r * 0.5/0.33; 
   light_ambient.a = 1.0;




// correct ambient light intensity and hue before sunrise
if (earthShade < 0.5)
	{
	//light_ambient = light_ambient * (0.7 + 0.3 * smoothstep(0.2, 0.5, earthShade));
	intensity = length(light_ambient.xyz); 

	light_ambient.rgb = intensity * normalize(mix(light_ambient.rgb,  shadedFogColor, 1.0 -smoothstep(0.1, 0.8,earthShade) ));
	light_ambient.rgb = light_ambient.rgb +   moonLightColor *  (1.0 - smoothstep(0.4, 0.5, earthShade));

	intensity = length(light_diffuse.xyz); 
	light_diffuse.rgb = intensity * normalize(mix(light_diffuse.rgb,  shadedFogColor, 1.0 -smoothstep(0.1, 0.7,earthShade) ));
	}


// the haze gets the light at the altitude of the haze top if the vertex in view is below
// but the light at the vertex if the vertex is above

vertex_alt = max(vertex_alt,hazeLayerAltitude);

if (vertex_alt > hazeLayerAltitude)
	{
	if (dist > 0.8 * avisibility)
		{
		vertex_alt = mix(vertex_alt, hazeLayerAltitude, smoothstep(0.8*avisibility, avisibility, dist));
		yprime_alt = yprime -sqrt(2.0 * EarthRadius * vertex_alt);
		}
	}
else
	{
	vertex_alt = hazeLayerAltitude;
	yprime_alt = yprime -sqrt(2.0 * EarthRadius * vertex_alt);
	}

}
else // the faster, full-day version without lightfields
{
    //vertex_alt = max(gl_Vertex.z,100.0);
 
    earthShade = 1.0;
    mie_angle = 1.0;
    
    if (terminator > 3000000.0)
    	{light_diffuse = vec4 (1.0, 1.0, 1.0, 0.0);
	light_ambient = vec4 (0.33, 0.4, 0.5, 0.0); }
    else
	{

	lightArg = (terminator/100000.0 - 10.0)/20.0;
	light_diffuse.b = 0.78  + lightArg * 0.21;
	light_diffuse.g = 0.907 + lightArg * 0.091;
	light_diffuse.r = 0.904 + lightArg * 0.092;
	light_diffuse.a = 1.0;

	light_ambient.r = 0.316 + lightArg * 0.016;
	light_ambient.g = light_ambient.r * 0.4/0.33; 
   	light_ambient.b = light_ambient.r * 0.5/0.33;
	light_ambient.a = 1.0;
	}  
    
    light_diffuse = light_diffuse * scattering;
    yprime_alt = -sqrt(2.0 * EarthRadius * hazeLayerAltitude);
}

	
			
			
			
        diffuse_term = diffuse_color * light_diffuse;
        vec4 ambient_term = ambient_color * light_ambient;

        // Super hack: if diffuse material alpha is less than 1, assume a
        // transparency animation is at work
        if (gl_FrontMaterial.diffuse.a < 1.0)
            diffuse_term.a = gl_FrontMaterial.diffuse.a;
        else
            diffuse_term.a = gl_Color.a;

        // Another hack for supporting two-sided lighting without using
        // gl_FrontFacing in the fragment shader.
        gl_FrontColor.rgb = ambient_term.rgb;  gl_FrontColor.a = 0.0;
        gl_BackColor.rgb = ambient_term.rgb; gl_FrontColor.a = 1.0;
//        fogCoord = abs(ecPosition.z / ecPosition.w);

        //fog_Func(fogType);

    }