LGL_format

LGL is the LateralGM
Library format, intended as a highly
compressed alternative to Game Maker's LIB
format.

Compression over LIB was achieved 3 ways:

• Trimming unused bytes (short strings are usually 1-byte prefixed)
  and unused inclusions (only include the arguments you use, not 8).
• Masking multiple booleans into 1 byte (also applies to values that
  don't use all 8 bits).
• Combining the Images into a single PNG strip. See
  #Image for more information.

As a result, LGLs are generally 10% of the size of their LIB equivalent.
The LIBs included with Game Maker are 860 KB. The LGLs included with
LateralGM, which contain the same number of Actions, are 82 KB.

The first downside is that readers have to cope with being able to read
2- and 3-byte integers, bit masks, and an image strip. This slightly
increases reading time. It normally takes LGM about 250ms (1/4 second)
to read and process all of its standard LGLs. The second downside is
limitations - a library can only have at most 127 actions, some strings
can must be shorter than 256 characters (names, action list/hint text,
argument info) - although these limitations are reasonable, since
libraries that exceed these limitations would behave undesirably in GM
anyways (imagine scrolling through hundreds of actions, or trying to
read a hint text that's wider than the screen).

For notes on how to read this format, and other information, please see
Format info. However, the following
differences exist in this format:

• Each line begins with the number of bytes that the information of
  that line requires, unless the line contains an insertion or a bit
  description.
• A >> denotes that a byte is broken up into bits, and the following
  lines describe those bits, each preceded by a > and a bit count
  (denoted by a "b" - e.g. "1b" indicates 1 bit)

Lookup Tables

ID	Name
0	Normal
1	Begin Group
2	End Group
3	Else
4	Exit
5	Repeat
6	Variable
7	Code
8	-Placeholder
9	-Separator
10	-Label

Action Kinds

ID	Name	Description
0	Nothing	Execution Information remains empty (0)
1	Function	Execution Information contains Function Name
2	Code	Execution Information contains Code

Execution Types

The Order column in the table below indicates the order that the
entries would be expected to appear in a user-friendly dropdown.

Order	Name	ID
1	Expression	0
2	String	1
3	Both	2
4	Boolean	3
5	Menu	4
6	Color	13
7	Font String	15
8	Sprite	5
9	Sound	6
10	Background	7
11	Path	8
12	Script	9
13	Object	10
14	Room	11
15	Font	12
16	Timeline	14

Argument Types

Documentation

3 (string) "LGL"
2 LGM version needed for the following info (160)
3 Lib ID (if ID < 1000, this file is protected as official)
1 Length of Tab Caption { Tab Caption }
1 Length of Author { Author }
4 Lib Version
8 (double) Last Changed date
4 Length of Info { Info }
4 Length of Initialization Code { Initialization Code }
1 >>
> 1b Advanced
> 7b Number of Actions
{
2 LGM version needed for the following info (160)
2 Action Id
1 Length of Name { Name }
1 Length of Description { Description }
1 Length of List Text { List Text }
1 Length of Hint Text { Hint Text }
1 >>
> 1b Hidden
> 1b Advanced
> 1b Registered only
> 1b Question
> 1b Apply to
> 1b Relative
> 2b Execution Type[1](0-2)
4 Length of Execution Information[2]{ Execution Information }
1 >>
> 4b Kind[3](0-10)
> 4b Interface Kind (0=Normal, 1=None, 2=Arrows, 5=Code, 6=Text)
1 Argument Count
{
1 Length of Argument Caption { Argument Caption }
1 Argument Type[4](0-15)
1 Length of Default Argument Value { Default Argument Value }
1 Length of Menu { Menu }
}
}
Raw PNG Strip of ActionImages

<references></references>

[5] [6] [7]

Image

In LGL, all of the Action
Images for a library are combined together into a single strip/sheet
PNG. By doing this, filesize is greatly reduced, because PNG compression
compresses a single large image better than a bunch of little images
(not to mention, there is only 1 header this way). Transparency is not
only supported, but expected.

The image sheet must be composed of 24x24 tiles. Tiles may be arranged
horizontally, vertically, or both. Tiles are to be read left-to-right
and then top-to-bottom. For an example, see the image included in this
section.

The PNG data storing the image sheet is appended raw to the end of the
LGL file. There is no length prefix (aside from the PNG-internal size
indicators in the PNG header data). Immediately after the last Action
and its Arguments, you will encounter the PNG signature (0x89 0x50 0x4E
0x47) and the rest of the PNG data. The LGL format does not specify any
additional data after the PNG, and it is generally expected that you
should encounter the End of the File (EOF) after the PNG data.

Category:Formats

1.
2.
3.
4.

1. Execution Information is an adapted value that depends on Execution
   Type (above).

2. See Action Kinds above

3. See Argument Types above