slang-shaders/include/gamma-management.h

#ifndef GAMMA_MANAGEMENT_H
#define GAMMA_MANAGEMENT_H

///////////////////////////////  BASE CONSTANTS  ///////////////////////////////

//  Set standard gamma constants, but allow users to override them:
#ifndef OVERRIDE_STANDARD_GAMMA
    //  Standard encoding gammas:
    const float ntsc_gamma = 2.2;    //  Best to use NTSC for PAL too?
    const float pal_gamma = 2.8;     //  Never actually 2.8 in practice
    //  Typical device decoding gammas (only use for emulating devices):
    //  CRT/LCD reference gammas are higher than NTSC and Rec.709 video standard
    //  gammas: The standards purposely undercorrected for an analog CRT's
    //  assumed 2.5 reference display gamma to maintain contrast in assumed
    //  [dark] viewing conditions: http://www.poynton.com/PDFs/GammaFAQ.pdf
    //  These unstated assumptions about display gamma and perceptual rendering
    //  intent caused a lot of confusion, and more modern CRT's seemed to target
    //  NTSC 2.2 gamma with circuitry.  LCD displays seem to have followed suit
    //  (they struggle near black with 2.5 gamma anyway), especially PC/laptop
    //  displays designed to view sRGB in bright environments.  (Standards are
    //  also in flux again with BT.1886, but it's underspecified for displays.)
    const float crt_reference_gamma_high = 2.5;  //  In (2.35, 2.55)
    const float crt_reference_gamma_low = 2.35;  //  In (2.35, 2.55)
    const float lcd_reference_gamma = 2.5;       //  To match CRT
    const float crt_office_gamma = 2.2;  //  Circuitry-adjusted for NTSC
    const float lcd_office_gamma = 2.2;  //  Approximates sRGB
#endif  //  OVERRIDE_STANDARD_GAMMA

//  Assuming alpha == 1.0 might make it easier for users to avoid some bugs,
//  but only if they're aware of it.
#ifndef OVERRIDE_ALPHA_ASSUMPTIONS
    const bool assume_opaque_alpha = false;
#endif


///////////////////////  DERIVED CONSTANTS AS FUNCTIONS  ///////////////////////

//  gamma-management.h should be compatible with overriding gamma values with
//  runtime user parameters, but we can only define other global constants in
//  terms of static constants, not uniform user parameters.  To get around this
//  limitation, we need to define derived constants using functions.

//  Set device gamma constants, but allow users to override them:
#ifdef OVERRIDE_DEVICE_GAMMA
    //  The user promises to globally define the appropriate constants:
    float get_crt_gamma()    {   return crt_gamma;   }
    float get_gba_gamma()    {   return gba_gamma;   }
    float get_lcd_gamma()    {   return lcd_gamma;   }
#else
    float get_crt_gamma()    {   return crt_reference_gamma_high;    }
    float get_gba_gamma()    {   return 3.5; }   //  Game Boy Advance; in (3.0, 4.0)
    float get_lcd_gamma()    {   return lcd_office_gamma;            }
#endif  //  OVERRIDE_DEVICE_GAMMA

//  Set decoding/encoding gammas for the first/lass passes, but allow overrides:
#ifdef OVERRIDE_FINAL_GAMMA
    //  The user promises to globally define the appropriate constants:
    float get_intermediate_gamma()   {   return intermediate_gamma;  }
    float get_input_gamma()          {   return input_gamma;         }
    float get_output_gamma()         {   return output_gamma;        }
#else
    //  If we gamma-correct every pass, always use ntsc_gamma between passes to
    //  ensure middle passes don't need to care if anything is being simulated:
    float get_intermediate_gamma()   {   return ntsc_gamma;          }
    #ifdef SIMULATE_CRT_ON_LCD
        float get_input_gamma()      {   return get_crt_gamma();     }
        float get_output_gamma()     {   return get_lcd_gamma();     }
    #else
    #ifdef SIMULATE_GBA_ON_LCD
        float get_input_gamma()      {   return get_gba_gamma();     }
        float get_output_gamma()     {   return get_lcd_gamma();     }
    #else
    #ifdef SIMULATE_LCD_ON_CRT
        float get_input_gamma()      {   return get_lcd_gamma();     }
        float get_output_gamma()     {   return get_crt_gamma();     }
    #else
    #ifdef SIMULATE_GBA_ON_CRT
        float get_input_gamma()      {   return get_gba_gamma();     }
        float get_output_gamma()     {   return get_crt_gamma();     }
    #else   //  Don't simulate anything:
        float get_input_gamma()      {   return ntsc_gamma;          }
        float get_output_gamma()     {   return ntsc_gamma;          }
    #endif  //  SIMULATE_GBA_ON_CRT
    #endif  //  SIMULATE_LCD_ON_CRT
    #endif  //  SIMULATE_GBA_ON_LCD
    #endif  //  SIMULATE_CRT_ON_LCD
#endif  //  OVERRIDE_FINAL_GAMMA

#ifndef GAMMA_ENCODE_EVERY_FBO
    #ifdef FIRST_PASS
        const bool linearize_input = true;
        float get_pass_input_gamma()     {   return get_input_gamma();   }
    #else
        const bool linearize_input = false;
        float get_pass_input_gamma()     {   return 1.0;                 }
    #endif
    #ifdef LAST_PASS
        const bool gamma_encode_output = true;
        float get_pass_output_gamma()    {   return get_output_gamma();  }
    #else
        const bool gamma_encode_output = false;
        float get_pass_output_gamma()    {   return 1.0;                 }
    #endif
#else
    const bool linearize_input = true;
    const bool gamma_encode_output = true;
    #ifdef FIRST_PASS
        float get_pass_input_gamma()     {   return get_input_gamma();   }
    #else
        float get_pass_input_gamma()     {   return get_intermediate_gamma();    }
    #endif
    #ifdef LAST_PASS
        float get_pass_output_gamma()    {   return get_output_gamma();  }
    #else
        float get_pass_output_gamma()    {   return get_intermediate_gamma();    }
    #endif
#endif

vec4 decode_input(const vec4 color)
{
    if(linearize_input)
    {
        if(assume_opaque_alpha)
        {
            return vec4(pow(color.rgb, vec3(get_pass_input_gamma())), 1.0);
        }
        else
        {
            return vec4(pow(color.rgb, vec3(get_pass_input_gamma())), color.a);
        }
    }
    else
    {
        return color;
    }
}

vec4 encode_output(const vec4 color)
{
    if(gamma_encode_output)
    {
        if(assume_opaque_alpha)
        {
            return vec4(pow(color.rgb, vec3(1.0/get_pass_output_gamma())), 1.0);
        }
        else
        {
            return vec4(pow(color.rgb, vec3(1.0/get_pass_output_gamma())), color.a);
        }
    }
    else
    {
        return color;
    }
}

#define tex2D_linearize(C, D) decode_input(vec4(texture(C, D)))
//vec4 tex2D_linearize(const sampler2D tex, const vec2 tex_coords)
//{   return decode_input(vec4(texture(tex, tex_coords)));   }

//#define tex2D_linearize(C, D, E) decode_input(vec4(texture(C, D, E)))
//vec4 tex2D_linearize(const sampler2D tex, const vec2 tex_coords, const int texel_off)
//{   return decode_input(vec4(texture(tex, tex_coords, texel_off)));    }

#endif  //  GAMMA_MANAGEMENT_H