Перевернуть небо

layout (location = 0) in vec3 inPos;
layout (location = 1) in vec3 inNormal;
layout (location = 2) in vec2 uv;
layout (location = 3) in vec3 inColor;

layout (location = 0) out vec2 outUV;
layout (location = 1) out  vec3   v;
layout (location = 2) out  vec3   l;
layout (location = 3) out  vec3   colorYxy;
layout (location = 4) out  float  lv;            // dot (  l, v )

out gl_PerVertex 
{
  vec4 gl_Position;
};

#define  EPS  0.1
vec3 perezZenith ( float t, float thetaSun )
{
  const float  pi = 3.1415926;
  const vec4  cx1 = vec4 ( 0,       0.00209, -0.00375, 0.00165  );
  const vec4  cx2 = vec4 ( 0.00394, -0.03202, 0.06377, -0.02903 );
  const vec4  cx3 = vec4 ( 0.25886, 0.06052, -0.21196, 0.11693  );
  const vec4  cy1 = vec4 ( 0.0,     0.00317, -0.00610, 0.00275  );
  const vec4  cy2 = vec4 ( 0.00516, -0.04153, 0.08970, -0.04214 );
  const vec4  cy3 = vec4 ( 0.26688, 0.06670, -0.26756, 0.15346  );

  float  t2    = t*t;              // turbidity squared
  float  chi   = (4.0 / 9.0 - t / 120.0 ) * (pi - 2.0 * thetaSun );
  vec4  theta = vec4 ( 1, thetaSun, thetaSun*thetaSun, thetaSun*thetaSun*thetaSun );

  float  Y = (4.0453 * t - 4.9710) * tan ( chi ) - 0.2155 * t + 2.4192;
  float  x = t2 * dot ( cx1, theta ) + t * dot ( cx2, theta ) + dot ( cx3, theta );
  float  y = t2 * dot ( cy1, theta ) + t * dot ( cy2, theta ) + dot ( cy3, theta );

  return vec3 ( Y, x, y );
}

vec3  perezFunc ( float t, float cosTheta, float cosGamma )
{
  float  gamma      = acos ( cosGamma );
  float  cosGammaSq = cosGamma * cosGamma;
  //float  aY =  0.17872 * t - 1.46303;
  //float  bY = -0.35540 * t + 0.42749;
  //float  cY = -0.02266 * t + 5.32505;
  //float  dY =  0.12064 * t - 2.57705;
  //float  eY = -0.06696 * t + 0.37027;
  //float  ax = -0.01925 * t - 0.25922;
  //float  bx = -0.06651 * t + 0.00081;
  //float  cx = -0.00041 * t + 0.21247;
  //float  dx = -0.06409 * t - 0.89887;
  //float  ex = -0.00325 * t + 0.04517;
  //float  ay = -0.01669 * t - 0.26078;
  //float  by = -0.09495 * t + 0.00921;
  //float  cy = -0.00792 * t + 0.21023;
  //float  dy = -0.04405 * t - 1.65369;
  //float  ey = -0.01092 * t + 0.05291;
  
  return vec3 ( (1.0 + ubo.A.x * exp(ubo.B.x/cosTheta)) * (1.0 + ubo.C.x * exp(ubo.D.x * gamma) + ubo.E.x * cosGammaSq),
                (1.0 + ubo.A.y * exp(ubo.B.y/cosTheta)) * (1.0 + ubo.C.y * exp(ubo.D.y * gamma) + ubo.E.y * cosGammaSq),
           (1.0 + ubo.A.z * exp(ubo.B.z/cosTheta)) * (1.0 + ubo.C.z * exp(ubo.D.z * gamma) + ubo.E.z * cosGammaSq));
}

vec3  perezSky (float cosTheta, float cosGamma)
{

#define COLOR_EXP  0
#define THETA_SUN   3

  float colorExp = ubo.skyVars[COLOR_EXP];
  float thetaSun = ubo.skyVars[THETA_SUN];
  //float  thetaSun = acos        ( cosThetaSun );
  vec3  zenith   = perezZenith ( colorExp, thetaSun );
  vec3  clrYxy   = zenith * perezFunc ( colorExp, cosTheta, cosGamma ) / perezFunc ( ubo.skyVars[COLOR_EXP], 1.0, l.y );
  
  clrYxy [0] *= smoothstep ( 0.0, EPS, l.y );      // make sure when thetaSun > PI/2 we have black color
  
  return clrYxy;
}

void main()
{
  vec3 poss = vec3(ubo.model * vec4(inPos,1));  
  gl_Position     = ubo.projView * vec4(poss,1);    
  v = normalize ( possss - ubo.viewPos.xyz);
  lv  = dot ( ubo.sunDir.xyz, v );

#define GORIZONT 0.0  // Линия горизонта 

  colorYxy        = perezSky (v.y + GORIZONT, lv);  
  outUV = uv;
}