uniform float u_fogMaxDist;
uniform float u_fogMinDist;
uniform vec4 u_fogColor;

varying vec4 v_eyePos;

float computeLinearFogFactor()
{
   float factor;

   // Compute linear fog equation
   factor = (u_fogMaxDist - length(v_eyePos.xyz)) /
            (u_fogMaxDist - u_fogMinDist );

   // Clamp in the [0,1] range
   factor = clamp( factor, 0.0, 1.0 );

   return factor;
}

vec4 getColorWithFog(vec4 baseColor)
{
    float a = baseColor.a;
    float fogFactor = computeLinearFogFactor();
    vec4  fogColor = fogFactor * u_fogColor;
    vec4 c = baseColor * fogFactor + fogColor * (1.0 - fogFactor);
    c.a = a;
    return c;
}