/**
 * @file atmosphericsV.glsl
 *
 * $LicenseInfo:firstyear=2005&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2005, Linden Research, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 * 
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */
 


// VARYING param funcs
void setSunlitColor(vec3 v);
void setAmblitColor(vec3 v);
void setAdditiveColor(vec3 v);
void setAtmosAttenuation(vec3 v);
void setPositionEye(vec3 v);

vec3 getAdditiveColor();

//VARYING vec4 vary_CloudUVs;
//VARYING float vary_CloudDensity;

// Inputs
uniform vec4 morphFactor;
uniform vec3 camPosLocal;
//uniform vec4 camPosWorld;

uniform vec4 lightnorm;
uniform vec4 sunlight_color;
uniform vec4 ambient;
uniform vec4 blue_horizon;
uniform vec4 blue_density;
uniform float haze_horizon;
uniform float haze_density;
uniform float cloud_shadow;
uniform float density_multiplier;
uniform float distance_multiplier;
uniform float max_y;
uniform vec4 glow;
uniform float sun_up_factor;

void calcAtmospherics(vec3 inPositionEye) {

    vec3 P = inPositionEye;
    setPositionEye(P);
    
    //(TERRAIN) limit altitude
    //if (P.y > max_y) P *= (max_y / P.y);
    //if (P.y < -max_y) P *= (-max_y / P.y);

    vec3 tmpLightnorm = lightnorm.xyz;

    vec3 Pn = normalize(P);
    float  Plen = length(P);

    vec4 temp1 = vec4(0);
    vec3 temp2 = vec3(0);
    vec4 blue_weight;
    vec4 haze_weight;
    vec4 sunlight = sunlight_color;
    vec4 light_atten;

    //sunlight attenuation effect (hue and brightness) due to atmosphere
    //this is used later for sunlight modulation at various altitudes
    light_atten = (blue_density + vec4(haze_density * 0.25)) * (density_multiplier * max_y);
        //I had thought blue_density and haze_density should have equal weighting,
        //but attenuation due to haze_density tends to seem too strong

    temp1 = blue_density + vec4(haze_density);
    blue_weight = blue_density / temp1;
    haze_weight = vec4(haze_density) / temp1;

    //(TERRAIN) compute sunlight from lightnorm only (for short rays like terrain)
    temp2.y = max(0.0, tmpLightnorm.y);
    temp2.y = 1. / temp2.y;
    sunlight *= exp( - light_atten * temp2.y);

    // main atmospheric scattering line integral
    temp2.z = Plen * density_multiplier;

    // Transparency (-> temp1)
    // ATI Bugfix -- can't store temp1*temp2.z*distance_multiplier in a variable because the ati
    // compiler gets confused.
    temp1 = exp(-temp1 * temp2.z * distance_multiplier);

    //final atmosphere attenuation factor
    setAtmosAttenuation(temp1.rgb);
    //vary_AtmosAttenuation = distance_multiplier / 10000.;
    //vary_AtmosAttenuation = density_multiplier * 100.;
    //vary_AtmosAttenuation = vec4(Plen / 100000., 0., 0., 1.);

    //compute haze glow
    //(can use temp2.x as temp because we haven't used it yet)
    temp2.x = dot(Pn, tmpLightnorm.xyz);
    temp2.x = 1. - temp2.x;
        //temp2.x is 0 at the sun and increases away from sun
    temp2.x = max(temp2.x, .03);    //was glow.y
        //set a minimum "angle" (smaller glow.y allows tighter, brighter hotspot)
    temp2.x *= glow.x;
        //higher glow.x gives dimmer glow (because next step is 1 / "angle")
    temp2.x = pow(temp2.x, glow.z);
        //glow.z should be negative, so we're doing a sort of (1 / "angle") function

        temp2.x *= sun_up_factor;

    //add "minimum anti-solar illumination"
    temp2.x += .25;

    //increase ambient when there are more clouds
    vec4 tmpAmbient = ambient + (vec4(1.) - ambient) * cloud_shadow * 0.5;

    vec3 additive = 
        vec3(blue_horizon * blue_weight * (sunlight*(1.-cloud_shadow) + tmpAmbient)
      + (haze_horizon * haze_weight) * (sunlight*(1.-cloud_shadow) * temp2.x
          + tmpAmbient));
    additive = normalize(additive);

    //haze color
    //setAdditiveColor(
    //  vec3(blue_horizon * blue_weight * (sunlight*(1.-cloud_shadow) + tmpAmbient)
    //  + (haze_horizon * haze_weight) * (sunlight*(1.-cloud_shadow) * temp2.x
    //    + tmpAmbient)));
    
    //brightness of surface both sunlight and ambient
    setSunlitColor(vec3(sunlight * .5));
    setAmblitColor(vec3(tmpAmbient * .25));
    setAdditiveColor(additive * vec3(1.0 - exp(-temp2.z * distance_multiplier)) * 0.5);

    // vary_SunlitColor = vec3(0);
    // vary_AmblitColor = vec3(0);
    // vary_AdditiveColor = vec4(Pn, 1.0);

    /*
    const float cloudShadowScale = 100.;
    // Get cloud uvs for shadowing
    vec3 cloudPos = inPositionEye + camPosWorld - cloudShadowScale / 2.;
    vary_CloudUVs.xy = cloudPos.xz / cloudShadowScale;

    // We can take uv1 and multiply it by (TerrainSpan / CloudSpan)
//  cloudUVs *= (((worldMaxZ - worldMinZ) * 20) /40000.);
    vary_CloudUVs *= (10000./40000.);

    // Offset by sun vector * (CloudAltitude / CloudSpan)
    vary_CloudUVs.x += tmpLightnorm.x / tmpLightnorm.y * (3000./40000.);
    vary_CloudUVs.y += tmpLightnorm.z / tmpLightnorm.y * (3000./40000.);
    */
}