out vec4 FragColor;
uniform sampler2D uTexMain;

in vec2 aUv;

float kPi = 3.14159265358979;

vec2 fisheye_distort(vec2 xy)
{
   float aperture = 1350.0;
   float apertureHalf = 0.5 * aperture * (kPi / 180.0);
   float maxFactor = sin(apertureHalf);

   vec2 uv;
   float d = length(xy);
   if(d < (2.0-maxFactor))
   {
      d = length(xy * maxFactor);
      float z = sqrt(1.0 - d * d);
      float r = atan(d, z) / kPi;
      float phi = atan(xy.y, xy.x);

      uv.x = r * cos(phi) + 0.5;
      uv.y = r * sin(phi) + 0.5;
   }
   else
   {
      uv = 0.5*xy + 0.5;
   }
   
   return uv;
}


void main()
{
   vec2 vwarp = 2.0*aUv - 1.0;
   vwarp = fisheye_distort( vwarp );

   FragColor = texture( uTexMain, aUv );
}