slang-shaders/include/gamma-management.h
2016-08-26 11:28:24 -05:00

165 lines
6.7 KiB
C

#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