Huey

Neovim lua color scheme generator written in Rust.

Huey makes it easy to create a minimal lua based neovim colorscheme with HSL based color generation.

The project takes inspiration from colorgen-nvim and borrows some of the data format semantics in the theme file but also enhanches it with HSL based functions.

Build project

The project is written in Rust and therefore built with cargo. To build and install the program locally run the following commands:

cargo build
cargo install --path .

The project also comes with a nix flake which provides an appropriate development environment and build hook. Experience with nix and a flake enabled nix installation are of course required for this option.

Enter dev shell:

nix develop

Build the default huey nix package:

nix build

Basic usage

The program requires a theme file and an optional positional argument for the output directory of the lua files: The following command generates a theme in the current working directory:

huey /path/to/my/awesome/theme.toml .

File format

Theme files are written in the toml format and contains the following sections:

• [hues] - dictionary of base hues to use in your colorscheme, can be referenced as variables in later sections
• [colors] - dictionary of colors to use in your colorscheme, can be created and manipulated with HSL based functions
• [highlights] - dictionary of the final nvim highlights, references the colors in the previous sections
• [globals] - dictionary of the color variables to be inserted under vim.g..., references the colors in the previous sections, i.e. not highlights
  • This section is useful for setting the colors of the integrated Neovim terminal: terminal_color_0 = "my_terminal_color"

Functions

The following functions are available in the colors section:

hsl(hue, saturation, lightness)

Takes a hue value (0-360), saturation value (0-1.0) and a lightness value (0-1.0) and creates a color variable. The hue value can use a variable from the [hues] section with the $ symbol.

adjust(existing-color, saturation, lightness)

Takes an already defined color and adjusts its saturation and lightness values with a delta. Keep in mind that the delta is not relative but absolute. A color with lightness 0.8 and a delta of -0.4 would result in a new color with lightness 0.4. Resulting saturation and lightness values are clamped between 0 and 1.

darken(existing-color, value)

Shorthand method for decreasing the lightness component of the color. Behaves as the adjust method without a saturation delta.

lighten(existing-color, value)

Shorthand method for increasing the lightness component of the color. Behaves as the adjust method without a saturation delta.

mix(color1, color2, weight)

Mixes two existing colors into a new one based ona weight. The weight is relative to the first color: 1.0 just returns the first color, 0.5 return a 50/50 mix of the two colors, 0.0 just returns the second color.

Regular hex color

It is also possible to declare colors with regular hex notation. The colors behave exactly the same as colors declared with HSL.

Highlights section

The format is very similar to colorgen-nvim:

• foreground background style special
• link:<name of hl group>

The '-' is used to skip a particular section and replace it with NONE

The style options are the following:

• o: standout
• u: underline
• c: undercurl
• d: underdouble
• t: underdotted
• h: underdashed
• s: strikethrough
• i: italic
• b: bold
• r: reverse
• n: nocombine

Example theme file

Full colorscheme example can be found here

name = "iceberg"
background = "dark"

[hues]
hue_base = 230

hue_red    = 0
hue_orange = 25
hue_green  = 70
hue_cyan   = 190
hue_blue   = 215
hue_purple = 255
hue_pale   = 225

[colors]
# palette
blue   = "hsl($hue_blue, 0.37, 0.65)"
green  = "hsl($hue_green, 0.32, 0.63)"
cyan   = "hsl($hue_cyan, 0.32, 0.65)"
orange = "hsl($hue_orange, 0.65, 0.68)"
purple = "hsl($hue_purple, 0.32, 0.68)"
red    = "hsl($hue_red, 0.65, 0.68)"
pale   = "hsl($hue_pale, 0.28, 0.72)"

hex_color = "#ff0000"

# normal
normal_bg = "hsl($hue_base, 0.20, 0.11)"
normal_fg = "hsl($hue_base, 0.10, 0.80)"

# linenr
linenr_bg       = "adjust(normal_bg, 0.05, 0.05)"
linenr_fg       = "lighten(linenr_bg, 0.20)"
cursorlinenr_bg = "adjust(linenr_bg, 0.10, 0.10)"
cursorlinenr_fg = "adjust(linenr_fg, 0.10, 0.50)"

[highlights]
Normal           = "normal_fg normal_bg"
ColorColumn      = "- cursorline_bg"
CursorColumn     = "- cursorline_bg"
CursorLine       = "- cursorline_bg"
Constant         = "purple - i" # italic
Cursor           = "normal_bg normal_fg"
CursorLineNr     = "cursorlinenr_fg cursorlinenr_bg"
Delimiter        = "normal_fg"
Directory        = "blue - b" # bold

# treesitter
"@attribute"             = "link:Special"
"@boolean"               = "link:Constant"
"@character"             = "link:Constant"
"@character.special"     = "link:Constant"
"@comment"               = "link:Comment"
"@conditional"           = "link:Statement"
"@constant.builtin"      = "link:Constant"
"@constant"              = "link:Constant"
"@constant.macro"        = "link:Constant"

[globals]
terminal_color_0 = "blue"
terminal_color_1 = "darken(green, 0.1)"