1// Adapted from https://github.com/microsoft/terminal/blob/1283c0f5b99a2961673249fa77c6b986efb5086c/src/renderer/atlas/dwrite.hlsl
 2// Copyright (c) Microsoft Corporation.
 3// Licensed under the MIT license.
 4
 5float color_brightness(float3 color) {
 6    // REC. 601 luminance coefficients for perceived brightness
 7    return dot(color, float3(0.30f, 0.59f, 0.11f));
 8}
 9
10float light_on_dark_contrast(float enhancedContrast, float3 color) {
11    float brightness = color_brightness(color);
12    float multiplier = saturate(4.0f * (0.75f - brightness));
13    return enhancedContrast * multiplier;
14}
15
16float enhance_contrast(float alpha, float k) {
17    return alpha * (k + 1.0f) / (alpha * k + 1.0f);
18}
19
20float3 enhance_contrast3(float3 alpha, float k) {
21    return alpha * (k + 1.0f) / (alpha * k + 1.0f);
22}
23
24float apply_alpha_correction(float a, float b, float4 g) {
25    float brightness_adjustment = g.x * b + g.y;
26    float correction = brightness_adjustment * a + (g.z * b + g.w);
27    return a + a * (1.0f - a) * correction;
28}
29
30float3 apply_alpha_correction3(float3 a, float3 b, float4 g) {
31    float3 brightness_adjustment = g.x * b + g.y;
32    float3 correction = brightness_adjustment * a + (g.z * b + g.w);
33    return a + a * (1.0f - a) * correction;
34}
35
36float apply_contrast_and_gamma_correction(float sample, float3 color, float enhanced_contrast_factor, float4 gamma_ratios) {
37    float enhanced_contrast = light_on_dark_contrast(enhanced_contrast_factor, color);
38    float brightness = color_brightness(color);
39
40    float contrasted = enhance_contrast(sample, enhanced_contrast);
41    return apply_alpha_correction(contrasted, brightness, gamma_ratios);
42}
43
44float3 apply_contrast_and_gamma_correction3(float3 sample, float3 color, float enhanced_contrast_factor, float4 gamma_ratios) {
45    float enhanced_contrast = light_on_dark_contrast(enhanced_contrast_factor, color);
46
47    float3 contrasted = enhance_contrast3(sample, enhanced_contrast);
48    return apply_alpha_correction3(contrasted, color, gamma_ratios);
49}