GRF coding

Revision as of 23:28, 11 May 2007

Writing NFO for smarties. Because you're not as dumb as you think you are.

Okay, welcome to my basic tutorial for coding grf sets.

What you will need

• A recent (ie, nightly) build of TTDPatch or, if you must, OpenTTD.
• GRFCodec
• NFORenum
• A coder's text editor (preferably something more advanced than notepad, since you'll want to be doing some formatting to make your NFO readable. NOT a rich text editor like wordpad).
• A graphics program of your choice that can manipulate .pcx and/or .png files.
• The newgrf spec.
• A computer running Windows, and/or the ability to translate what I say in Windows-speak into the language of your operating system. Creating and testing grfs on non-Windows systems may have additional challenges.

Getting set up

• Install grfcodec into a directory under/near your TTD directory.
• Copy trg1r.grf to this directory (and, if you like, the other default grfs) and decompile them with grfcodec. (grfcodec -d trg1r.grf -p2).
  • Resist the temptation to decode any other grf and have a look at what comes out. It will not be useful to you at this point. Believe me.
• Install NFOrenum into <grfcodec directory>/SPRITES, which should have been created when you decoded trg1r.grf.

And you're ready to go!

Getting started

Every grf file comes from an NFO file; the NFO file is, in essence, the source code of the grf. NFO files contain series of hex digits; however; don't let this put you off, as you can use comments, formatting, escape codes and quoted strings to make your NFO more human-readable.

Let's begin your first NFO file. Open your text editor and create a new file. Save it in <grfcodec directory>/SPRITES as <filename>.nfo

There are two things every NFO file must contain, other than the sprite lines that actually have data for vehicles or other features. They are the header, and the action 8.

The header

The header tells grfcodec how to encode the NFO. It looks like this:

// Automatically generated by GRFCODEC. Do not modify!
// (Info version 7)
// Format: spritenum pcxfile xpos ypos compression ysize xsize xrel yrel

You can copy and paste that, or alternatively you can let NFOrenum put the header in the first time you renum your file.

The action 8

Read the wiki page

The action 8 identifies your grf file. It's like the title page of a book.

An action 8 might look like this:

1 * 1	 08 07 "EA54" "My first Newgrf" 00 "By Joe Bloggs" 00

"EA54" is the grfid. It's important that every grf has a different ID: most grf authors use their intials for the first two characters.