// -*-C++-*-
#version 120

// 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.
// Haze part added by Thorsten Renk, Oct. 2011


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

// The constant 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 vec2 rawPos;
varying vec3 worldPos;


varying float mie_angle;
varying float steepness;


uniform int colorMode;
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 eye_alt;
uniform float moonlight;

uniform bool use_IR_vision;

uniform mat4 osg_ViewMatrixInverse;

float earthShade;
float yprime_alt;
//float mie_angle;


// 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;

vec3 moonlight_perception (in vec3 light);

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));
}


void main()
{

  vec4 light_diffuse;
  vec4 light_ambient;
  vec3 shadedFogColor = vec3(0.55, 0.67, 0.88);
  vec3 moonLightColor = vec3 (0.095, 0.095, 0.15) * moonlight;
  moonLightColor = moonlight_perception (moonLightColor);

  //float yprime_alt;
  float yprime;
  float lightArg;
  float intensity;
  float vertex_alt;
  float scattering;

    rawPos = gl_Vertex.xy;
    worldPos = (osg_ViewMatrixInverse *gl_ModelViewMatrix * gl_Vertex).xyz;
    steepness = dot(normalize(gl_Normal), vec3 (0.0, 0.0, 1.0));


// this code is copied from default.vert

    //vec4 ecPosition = gl_ModelViewMatrix * gl_Vertex;
    gl_Position = ftransform();
    gl_TexCoord[0] = gl_TextureMatrix[0] * gl_MultiTexCoord0;
    normal = gl_NormalMatrix * gl_Normal;
    //nvec = (gl_NormalMatrix * gl_Normal).xy;
    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;
    }
   
    

    // here start computations for the haze layer
    // we need several geometrical quantities

    
// 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;
    
    //ecViewdir = (gl_ModelViewMatrix * (ep - gl_Vertex)).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); 


// early culling of vertices which can't be seen due to ground haze despite being in aloft visibility range

//float delta_z = hazeLayerAltitude - eye_alt;
//if (((dist * (relPos.z - delta_z)/relPos.z >  visibility ) && (relPos.z < 0.0) && (delta_z < 0.0) && (dist > 30000.0)))
if (0==1)
	{
	gl_Position = vec4(0.0, 0.0, -1000.0, 1.0); // move outside of view frustrum, gets culled before reaching fragment shader
   	earthShade = 1.0;
    	mie_angle = 1.0;
	yprime_alt = 0.0;
	}
else
	{


    // 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.b = light_func(lightArg, 0.000506, 0.131, -3.315, 0.000457, 0.5);
   //light_ambient.g = light_func(lightArg, 2.264e-05, 0.134, 0.967, 3.66e-05, 0.4);
   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_func(lightArg, 0.236, 0.253, 1.073, 0.572, 0.4);
   light_ambient.b = light_ambient.r * 0.5/0.33; //light_func(lightArg, 0.236, 0.253, 1.073, 0.572, 0.5);
   light_ambient.a = 1.0;




// correct ambient light intensity and hue before sunrise
if (earthShade < 0.5)
	{
	intensity = length(light_ambient.rgb); 
	light_ambient.rgb = intensity * normalize(mix(light_ambient.rgb,  shadedFogColor, 1.0 -smoothstep(0.4, 0.8,earthShade) ));
	light_ambient.rgb = light_ambient.rgb +   moonLightColor *  (1.0 - smoothstep(0.4, 0.5, earthShade));

	intensity = length(light_diffuse.rgb); 
	light_diffuse.rgb = intensity * normalize(mix(light_diffuse.rgb,  shadedFogColor, 1.0 -smoothstep(0.4, 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, 1.0);
	light_ambient = vec4 (0.33, 0.4, 0.5, 1.0); }
    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.b = 0.41 + lightArg * 0.08;
	//light_ambient.g = 0.333 + lightArg * 0.06;
	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);
}
 

// a sky/earth irradiation map model - the sky creates much more diffuse radiation than the ground, so
// steep faces end up shaded more

light_ambient = light_ambient * ((1.0+steepness)/2.0 * 1.2 + (1.0-steepness)/2.0 * 0.2);


// deeper shadows when there is lots of direct light

float shade_depth =  1.0 * smoothstep (0.6,0.95,ground_scattering) * (1.0-smoothstep(0.1,0.5,overcast)) * smoothstep(0.4,1.5,earthShade);

   light_ambient.rgb = light_ambient.rgb * (1.0 - shade_depth);
   light_diffuse.rgb = light_diffuse.rgb * (1.0 + 1.2 * shade_depth);

if (use_IR_vision)
	{
	light_ambient.rgb = max(light_ambient.rgb, vec3 (0.5, 0.5, 0.5));
	}

// default lighting based on texture and material using the light we have just computed

 diffuse_term = diffuse_color* light_diffuse;
    vec4 constant_term = gl_FrontMaterial.emission + ambient_color *
        (gl_LightModel.ambient +  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;
   diffuse_term.a = yprime_alt;
    // Another hack for supporting two-sided lighting without using
    // gl_FrontFacing in the fragment shader.
    gl_FrontColor.rgb = constant_term.rgb;  //gl_FrontColor.a = 1.0;
    gl_BackColor.rgb = constant_term.rgb; //gl_BackColor.a = 0.0;
    gl_FrontColor.a = mie_angle;
    gl_BackColor.a = mie_angle;
}
	
}