/**
 * @license
 * Copyright (c) 2000-2005, Sean O'Neil (s_p_oneil@hotmail.com)
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * * Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * * Neither the name of the project nor the names of its contributors may be
 *   used to endorse or promote products derived from this software without
 *   specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Modifications made by Analytical Graphics, Inc.
 */

 // Code:  http://sponeil.net/
 // GPU Gems 2 Article:  https://developer.nvidia.com/gpugems/GPUGems2/gpugems2_chapter16.html

#ifdef COLOR_CORRECT
uniform vec3 u_hsbShift; // Hue, saturation, brightness
#endif

uniform vec4 u_cameraAndRadiiAndDynamicAtmosphereColor; // Camera height, outer radius, inner radius, dynamic atmosphere color flag

const float g = -0.95;
const float g2 = g * g;

varying vec3 v_rayleighColor;
varying vec3 v_mieColor;
varying vec3 v_toCamera;
varying vec3 v_positionEC;

void main (void)
{
    float lightEnum = u_cameraAndRadiiAndDynamicAtmosphereColor.w;
    vec3 lightDirection =
        czm_viewerPositionWC * float(lightEnum == 0.0) +
        czm_lightDirectionWC * float(lightEnum == 1.0) +
        czm_sunDirectionWC * float(lightEnum == 2.0);
    lightDirection = normalize(lightDirection);

    // Extra normalize added for Android
    float cosAngle = dot(lightDirection, normalize(v_toCamera)) / length(v_toCamera);
    float rayleighPhase = 0.75 * (1.0 + cosAngle * cosAngle);
    float miePhase = 1.5 * ((1.0 - g2) / (2.0 + g2)) * (1.0 + cosAngle * cosAngle) / pow(1.0 + g2 - 2.0 * g * cosAngle, 1.5);

    vec3 rgb = rayleighPhase * v_rayleighColor + miePhase * v_mieColor;

#ifndef HDR
    const float exposure = 2.0;
    rgb = vec3(1.0) - exp(-exposure * rgb);
#endif

#ifdef COLOR_CORRECT
    // Convert rgb color to hsb
    vec3 hsb = czm_RGBToHSB(rgb);
    // Perform hsb shift
    hsb.x += u_hsbShift.x; // hue
    hsb.y = clamp(hsb.y + u_hsbShift.y, 0.0, 1.0); // saturation
    hsb.z = hsb.z > czm_epsilon7 ? hsb.z + u_hsbShift.z : 0.0; // brightness
    // Convert shifted hsb back to rgb
    rgb = czm_HSBToRGB(hsb);
#endif

    // Alter alpha based on how close the viewer is to the ground (1.0 = on ground, 0.0 = at edge of atmosphere)
    float atmosphereAlpha = clamp((u_cameraAndRadiiAndDynamicAtmosphereColor.y - u_cameraAndRadiiAndDynamicAtmosphereColor.x) / (u_cameraAndRadiiAndDynamicAtmosphereColor.y - u_cameraAndRadiiAndDynamicAtmosphereColor.z), 0.0, 1.0);

    // Alter alpha based on time of day (0.0 = night , 1.0 = day)
    float nightAlpha = (lightEnum != 0.0) ? clamp(dot(normalize(czm_viewerPositionWC), lightDirection), 0.0, 1.0) : 1.0;
    atmosphereAlpha *= pow(nightAlpha, 0.5);

    gl_FragColor = vec4(rgb, mix(rgb.b, 1.0, atmosphereAlpha) * smoothstep(0.0, 1.0, czm_morphTime));
}