nixcfg/homeManagerModules/desktopEnv/hypr/hyprshade/default.nix

{ pkgs, lib, config, ... }: {

  options = {
    desktopEnv.hyprland.hyprshade.enable =
      lib.mkEnableOption "Enables hyprshade with blue light filter.";
  };

  config = lib.mkIf config.desktopEnv.hyprland.hyprshade.enable {

    # Packages that should be installed to the user profile.
    home.packages = with pkgs; [ hyprshade ];

    xdg.configFile."hypr/shaders/blue-light-filter.glsl".text = ''
      // from https://github.com/hyprwm/Hyprland/issues/1140#issuecomment-1335128437

      precision highp float;
      varying vec2 v_texcoord;
      uniform sampler2D tex;

      const float temperature = 4500.0;
      const float temperatureStrength = 1.0;

      #define WithQuickAndDirtyLuminancePreservation
      const float LuminancePreservationFactor = 1.0;

      // function from https://www.shadertoy.com/view/4sc3D7
      // valid from 1000 to 40000 K (and additionally 0 for pure full white)
      vec3 colorTemperatureToRGB(const in float temperature) {
          // values from: http://blenderartists.org/forum/showthread.php?270332-OSL-Goodness&p=2268693&viewfull=1#post2268693
          mat3 m = (temperature <= 6500.0) ? mat3(vec3(0.0, -2902.1955373783176, -8257.7997278925690),
                                                  vec3(0.0, 1669.5803561666639, 2575.2827530017594),
                                                  vec3(1.0, 1.3302673723350029, 1.8993753891711275))
                                          : mat3(vec3(1745.0425298314172, 1216.6168361476490, -8257.7997278925690),
                                                  vec3(-2666.3474220535695, -2173.1012343082230, 2575.2827530017594),
                                                  vec3(0.55995389139931482, 0.70381203140554553, 1.8993753891711275));
          return mix(clamp(vec3(m[0] / (vec3(clamp(temperature, 1000.0, 40000.0)) + m[1]) + m[2]), vec3(0.0), vec3(1.0)),
                    vec3(1.0), smoothstep(1000.0, 0.0, temperature));
      }

      void main() {
          vec4 pixColor = texture2D(tex, v_texcoord);

          // RGB
          vec3 color = vec3(pixColor[0], pixColor[1], pixColor[2]);

      #ifdef WithQuickAndDirtyLuminancePreservation
          color *= mix(1.0, dot(color, vec3(0.2126, 0.7152, 0.0722)) / max(dot(color, vec3(0.2126, 0.7152, 0.0722)), 1e-5),
                      LuminancePreservationFactor);
      #endif

          color = mix(color, color * colorTemperatureToRGB(temperature), temperatureStrength);

          vec4 outCol = vec4(color, pixColor[3]);

          gl_FragColor = outCol;
      }
    '';
    xdg.configFile."hypr/hyprshade.toml".text = ''
      [[shades]]
      name = "blue-light-filter"
      start_time = 19:00:00
      end_time = 06:00:00
    '';
  };
}