GIMP brush file version 2: Lua parsing library

GIMP brush format is native to the GIMP image editor for storing a brush or a texture. It can be used in all Paint Tools, for example Pencil and Paintbrush. It works by repeating the brush bitmap as you move the tool. The Spacing parameter sets the distance between the brush marks as a percentage of brush width. Its default value can be set in the brush file.

You can also use GIMP to create new brushes in this format. Custom brushes can be loaded into GIMP for use in the paint tools by copying them into one of the Brush Folders - select Edit > Preferences in the menu bar, expand the Folders section and choose Brushes to see the recognized Brush Folders or to add new ones.

Application

GIMP (GNU Image Manipulation Program)

File extension

gbr

KS implementation details

License: CC0-1.0
Minimal Kaitai Struct required: 0.9

References

This page hosts a formal specification of GIMP brush file version 2 using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Lua source code to parse GIMP brush file version 2

gimp_brush.lua

-- This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
--
-- This file is compatible with Lua 5.3

local class = require("class")
require("kaitaistruct")
local enum = require("enum")
local stringstream = require("string_stream")
local str_decode = require("string_decode")

-- 
-- GIMP brush format is native to the GIMP image editor for storing a brush or a texture.
-- It can be used in all [Paint Tools](https://docs.gimp.org/2.10/en/gimp-tools-paint.html),
-- for example Pencil and Paintbrush. It works by repeating the brush bitmap as you move
-- the tool. The Spacing parameter sets the distance between the brush marks as a percentage
-- of brush width. Its default value can be set in the brush file.
-- 
-- You can also use GIMP to create new brushes in this format. Custom brushes can be loaded
-- into GIMP for use in the paint tools by copying them into one of the Brush Folders -
-- select **Edit** > **Preferences** in the menu bar, expand the **Folders** section
-- and choose **Brushes** to see the recognized Brush Folders or to add new ones.
-- See also: Source (https://gitlab.gnome.org/GNOME/gimp/-/raw/4416313/devel-docs/gbr.txt)
GimpBrush = class.class(KaitaiStruct)

GimpBrush.ColorDepth = enum.Enum {
  grayscale = 1,
  rgba = 4,
}

function GimpBrush:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function GimpBrush:_read()
  self.len_header = self._io:read_u4be()
  self._raw_header = self._io:read_bytes((self.len_header - 4))
  local _io = KaitaiStream(stringstream(self._raw_header))
  self.header = GimpBrush.Header(_io, self, self._root)
end

GimpBrush.property.len_body = {}
function GimpBrush.property.len_body:get()
  if self._m_len_body ~= nil then
    return self._m_len_body
  end

  self._m_len_body = ((self.header.width * self.header.height) * self.header.bytes_per_pixel.value)
  return self._m_len_body
end

GimpBrush.property.body = {}
function GimpBrush.property.body:get()
  if self._m_body ~= nil then
    return self._m_body
  end

  local _pos = self._io:pos()
  self._io:seek(self.len_header)
  self._m_body = self._io:read_bytes(self.len_body)
  self._io:seek(_pos)
  return self._m_body
end


GimpBrush.Header = class.class(KaitaiStruct)

function GimpBrush.Header:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function GimpBrush.Header:_read()
  self.version = self._io:read_u4be()
  if not(self.version == 2) then
    error("not equal, expected " ..  2 .. ", but got " .. self.version)
  end
  self.width = self._io:read_u4be()
  if not(self.width >= 1) then
    error("ValidationLessThanError")
  end
  if not(self.width <= 10000) then
    error("ValidationGreaterThanError")
  end
  self.height = self._io:read_u4be()
  if not(self.height >= 1) then
    error("ValidationLessThanError")
  end
  if not(self.height <= 10000) then
    error("ValidationGreaterThanError")
  end
  self.bytes_per_pixel = GimpBrush.ColorDepth(self._io:read_u4be())
  self.magic = self._io:read_bytes(4)
  if not(self.magic == "\071\073\077\080") then
    error("not equal, expected " ..  "\071\073\077\080" .. ", but got " .. self.magic)
  end
  self.spacing = self._io:read_u4be()
  self.brush_name = str_decode.decode(KaitaiStream.bytes_terminate(self._io:read_bytes_full(), 0, false), "UTF-8")
end

-- 
-- See also: Source (https://github.com/GNOME/gimp/blob/9b6d59f/app/core/gimpbrush-load.c#L170)
-- See also: Source (https://github.com/GNOME/gimp/blob/9b6d59f/app/core/gimpbrush-header.h#L24)
-- 
-- See also: Source (https://github.com/GNOME/gimp/blob/9b6d59f/app/core/gimpbrush-load.c#L177)
-- See also: Source (https://github.com/GNOME/gimp/blob/9b6d59f/app/core/gimpbrush-header.h#L24)
-- 
-- Default spacing to be used for brush. Percentage of brush width.

GimpBrush.Bitmap = class.class(KaitaiStruct)

function GimpBrush.Bitmap:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function GimpBrush.Bitmap:_read()
  self.rows = {}
  for i = 0, self._root.header.height - 1 do
    self.rows[i + 1] = GimpBrush.Row(self._io, self, self._root)
  end
end


GimpBrush.Row = class.class(KaitaiStruct)

function GimpBrush.Row:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function GimpBrush.Row:_read()
  self.pixels = {}
  for i = 0, self._root.header.width - 1 do
    local _on = self._root.header.bytes_per_pixel
    if _on == GimpBrush.ColorDepth.grayscale then
      self.pixels[i + 1] = GimpBrush.Row.PixelGray(self._io, self, self._root)
    elseif _on == GimpBrush.ColorDepth.rgba then
      self.pixels[i + 1] = GimpBrush.Row.PixelRgba(self._io, self, self._root)
    end
  end
end


GimpBrush.Row.PixelGray = class.class(KaitaiStruct)

function GimpBrush.Row.PixelGray:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function GimpBrush.Row.PixelGray:_read()
  self.gray = self._io:read_u1()
end

GimpBrush.Row.PixelGray.property.red = {}
function GimpBrush.Row.PixelGray.property.red:get()
  if self._m_red ~= nil then
    return self._m_red
  end

  self._m_red = 0
  return self._m_red
end

GimpBrush.Row.PixelGray.property.green = {}
function GimpBrush.Row.PixelGray.property.green:get()
  if self._m_green ~= nil then
    return self._m_green
  end

  self._m_green = 0
  return self._m_green
end

GimpBrush.Row.PixelGray.property.blue = {}
function GimpBrush.Row.PixelGray.property.blue:get()
  if self._m_blue ~= nil then
    return self._m_blue
  end

  self._m_blue = 0
  return self._m_blue
end

GimpBrush.Row.PixelGray.property.alpha = {}
function GimpBrush.Row.PixelGray.property.alpha:get()
  if self._m_alpha ~= nil then
    return self._m_alpha
  end

  self._m_alpha = self.gray
  return self._m_alpha
end


GimpBrush.Row.PixelRgba = class.class(KaitaiStruct)

function GimpBrush.Row.PixelRgba:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function GimpBrush.Row.PixelRgba:_read()
  self.red = self._io:read_u1()
  self.green = self._io:read_u1()
  self.blue = self._io:read_u1()
  self.alpha = self._io:read_u1()
end