HLG checkup shader for MPC-BE

HLG_to_sRGB.hlsl

// $MinimumShaderProfile: ps_2_0

sampler s0 : register(s0);

// float ST2084_to_Y(float pixel) // pixel should be 0-1
// {
//   const float pq_m1 = 0.1593017578125f; // ( 2610.0 / 4096.0 ) / 4.0;
//   const float pq_m2 = 78.84375f;        // ( 2523.0 / 4096.0 ) * 128.0;
//   const float pq_c1 = 0.8359375f;  // 3424.0 / 4096.0 or pq_c3 - pq_c2 + 1.0;
//   const float pq_c2 = 18.8515625f; // ( 2413.0 / 4096.0 ) * 32.0;
//   const float pq_c3 = 18.6875f;    // ( 2392.0 / 4096.0 ) * 32.0;
//   const float pq_C = 100.0f;
//   // Note that this does NOT handle any of the signal range
//   // considerations from 2084 - this assumes full range (0 - 1)
//   float Np = pow(pixel, 1.0f / pq_m2);
//   float L = Np - pq_c1;
//   if (L < 0.0)
//     L = 0.0;
//   L = L / (pq_c2 - pq_c3 * Np);
//   L = pow(L, 1.0f / pq_m1);
//   return L * pq_C; // returns 0-100, 1=100cd/m^2
// }
// float3 ST2084_to_Y(float3 rgb) {
//   return float3(ST2084_to_Y(rgb.x), ST2084_to_Y(rgb.y), ST2084_to_Y(rgb.z));
// }

float Y_to_sRGB(float C) // returns signal, 0-1, input 0-1
{
  return (C < 0.f)
             ? 0.f
             : ((C > 1.f) ? 1.f
                          : ((C < 0.0031308f)
                                 ? C * 12.92f
                                 : (1.055f * pow(C, 1.0f / 2.4f) - 0.055f)));
}
float3 Y_to_sRGB_3(float3 rgb) {
  return float3(Y_to_sRGB(rgb.x), Y_to_sRGB(rgb.y), Y_to_sRGB(rgb.z));
}

float HLG_to_Y(float C) {
  const float a = 0.17883277f;
  const float b = 0.28466892f;
  const float c = 0.55991073f;
  return (C < 0.f) ? 0.f : ((C <= 0.5f) ? (4.f * C * C) : exp((C - c) / a) + b);
}

float3 HLG_to_Y_3(float3 rgb) {
  return float3(HLG_to_Y(rgb.x), HLG_to_Y(rgb.y), HLG_to_Y(rgb.z));
}

float3 reinhard(float3 rgb){
    return rgb / (rgb+1);
}

float4 main(float2 tex : TEXCOORD0) : COLOR {
    float gain=1.f;
    float4 c0 = tex2D(s0, tex);
    float3 l = reinhard(HLG_to_Y_3(c0.xyz)*gain);
    float4 c = float4(Y_to_sRGB_3(l),1.);
    return c;
}