/** 
 * @file WLCloudsF.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
 * $/LicenseInfo$
 */

/*[EXTRA_CODE_HERE]*/ 

#ifdef DEFINE_GL_FRAGCOLOR
out vec4 frag_data[3];
#else
#define frag_data gl_FragData
#endif

/////////////////////////////////////////////////////////////////////////
// The fragment shader for the sky
/////////////////////////////////////////////////////////////////////////

VARYING vec4 vary_CloudColorSun;
VARYING vec4 vary_CloudColorAmbient;
VARYING float vary_CloudDensity;

uniform sampler2D cloud_noise_texture;
uniform sampler2D cloud_noise_texture_next;
uniform float blend_factor;
uniform vec4 cloud_pos_density1;
uniform vec4 cloud_pos_density2;
uniform vec4 gamma;
uniform float cloud_scale;
uniform float cloud_variance;

VARYING vec2 vary_texcoord0;
VARYING vec2 vary_texcoord1;
VARYING vec2 vary_texcoord2;
VARYING vec2 vary_texcoord3;

/// Soft clips the light with a gamma correction
vec3 scaleSoftClip(vec3 light);

vec4 cloudNoise(vec2 uv)
{
   vec4 a = texture2D(cloud_noise_texture, uv);
   vec4 b = texture2D(cloud_noise_texture_next, uv);
   vec4 cloud_noise_sample = mix(a, b, blend_factor);
   return cloud_noise_sample;
}

void main()
{
	// Set variables
	vec2 uv1 = vary_texcoord0.xy;
	vec2 uv2 = vary_texcoord1.xy;

	vec4 cloudColorSun = vary_CloudColorSun;
	vec4 cloudColorAmbient = vary_CloudColorAmbient;
	float cloudDensity = vary_CloudDensity;
	vec2 uv3 = vary_texcoord2.xy;
	vec2 uv4 = vary_texcoord3.xy;

    vec2 disturbance  = vec2(cloudNoise(uv1 / 8.0f).x, cloudNoise((uv3 + uv1) / 16.0f).x) * cloud_variance * (1.0f - cloud_scale * 0.25f);
    vec2 disturbance2 = vec2(cloudNoise((uv1 + uv3) / 4.0f).x, cloudNoise((uv4 + uv2) / 8.0f).x) * cloud_variance * (1.0f - cloud_scale * 0.25f);

	// Offset texture coords
	uv1 += cloud_pos_density1.xy + (disturbance * 0.02);	//large texture, visible density
	uv2 += cloud_pos_density1.xy;	//large texture, self shadow
	uv3 += cloud_pos_density2.xy;	//small texture, visible density
	uv4 += cloud_pos_density2.xy;	//small texture, self shadow

    float density_variance = min(1.0, (disturbance.x* 2.0 + disturbance.y* 2.0 + disturbance2.x + disturbance2.y));

    cloudDensity *= 1.0 - (density_variance * density_variance);

	// Compute alpha1, the main cloud opacity

	float alpha1 = (cloudNoise(uv1).x - 0.5) + (cloudNoise(uv3).x - 0.5) * cloud_pos_density2.z;
	alpha1 = min(max(alpha1 + cloudDensity, 0.) * 10 * cloud_pos_density1.z, 1.);

	// And smooth
	alpha1 = 1. - alpha1 * alpha1;
	alpha1 = 1. - alpha1 * alpha1;	

    if (alpha1 < 0.001f)
    {
        discard;
    }

	// Compute alpha2, for self shadowing effect
	// (1 - alpha2) will later be used as percentage of incoming sunlight
	float alpha2 = (cloudNoise(uv2).x - 0.5);
	alpha2 = min(max(alpha2 + cloudDensity, 0.) * 2.5 * cloud_pos_density1.z, 1.);

	// And smooth
	alpha2 = 1. - alpha2;
	alpha2 = 1. - alpha2 * alpha2;	

	// Combine
	vec4 color;
	color = (cloudColorSun*(1.-alpha2) + cloudColorAmbient);
	color *= 2.;

	/// Gamma correct for WL (soft clip effect).
	frag_data[0] = vec4(scaleSoftClip(color.rgb), alpha1);
	frag_data[1] = vec4(0.0,0.0,0.0,0.0);
	frag_data[2] = vec4(0,0,1,0);
}