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/*
* Stellarium
* Copyright (C) 2002-2022 Fabien Chereau and Stellarium contributors
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA.
*/
// Variables for the color computation
uniform highp vec3 sunPos;
uniform mediump float term_x, Ax, Bx, Cx, Dx, Ex;
uniform mediump float term_y, Ay, By, Cy, Dy, Ey;
// The current projection matrix
uniform mediump mat4 projectionMatrix;
// Contains the 2d position of the point on the screen (before multiplication by the projection matrix)
ATTRIBUTE mediump vec2 skyVertex;
// Contains the r,g,b,Y (luminosity) components.
ATTRIBUTE highp vec4 skyColor;
// The output variable passed to the fragment shader
VARYING mediump vec3 resultSkyColor;
vec3 xyYToRGB(highp float x, highp float y, highp float Y);
void main()
{
gl_Position = projectionMatrix*vec4(skyVertex, 0., 1.);
///////////////////////////////////////////////////////////////////////////
// First compute the xy color component
// skyColor contains the unprojected vertex position in r,g,b
// + the Y (luminance) component of the color in the alpha channel
highp vec3 unprojectedVertex = skyColor.xyz;
highp float Y = skyColor.w;
highp float cosDistSunq = dot(sunPos,unprojectedVertex);
highp float distSun=acos(cosDistSunq);
highp float oneOverCosZenithAngle = (unprojectedVertex.z==0.) ? 9999999999999. : 1. / unprojectedVertex.z;
cosDistSunq*=cosDistSunq;
highp float x = term_x * (1. + Ax * exp(Bx*oneOverCosZenithAngle))* (1. + Cx * exp(Dx*distSun) + Ex * cosDistSunq);
highp float y = term_y * (1. + Ay * exp(By*oneOverCosZenithAngle))* (1. + Cy * exp(Dy*distSun) + Ey * cosDistSunq);
if (x < 0. || y < 0.)
{
x = 0.25;
y = 0.25;
}
resultSkyColor=xyYToRGB(x,y,Y);
}
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