GRF coding

2009-04-12T06:12:22Z

Bennythen00b: I added a better description of how to decompile a .grf file.

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.

__TOC__
==What you will need==
*A recent (ie, nightly) build of TTDPatch or, if you must, OpenTTD.
*[http://www.ttdpatch.net/grfcodec/ GRFCodec]
*[http://users.tt-forums.net/dalestan/nforenum/ 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.
*[http://wiki.ttdpatch.net/tiki-index.php?page=NewGraphicsSpecs 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. (Open a new document in Notepad and copy paste this line into it: '''grfcodec -d trg1r.grf -p2'''. Save the document as *Whatever you want*.bat. The name isn't important, but remember the ".bat" Now double click the document you just made.).
**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 three things every NFO file must contain, other than the sprite lines that actually have data for vehicles or other features. They are the header, sprite 0 and the action 8.

===The header===

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

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

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

===Sprite 0===

This sprite follows after the header, and tells grfcodec the total sprite count. NFOrenum will insert this sprite.

===The action 8===

''Read [http://wiki.ttdpatch.net/tiki-index.php?page=Action8 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:
<pre>
1 * 1 08 07 "JB01" "My first Newgrf" 00 "By Joe Bloggs" 00
</pre>
"JB01" is the grfid. It's important that every grf has a different ID: most grf authors use their intials for the first two characters.

==Anatomy of an NFO==

Asides from the header, sprite 0 and action 8, you need some sprites and psuedosprites that actually do something.

*[[A vehicle (NFO)]]
*[[Example NFO files]]

==Compiling the grf==

Hopefully you can work out how to do this yourself. However, here's a few tips:

*Always renum your nfo file before compiling, and check for errors (search the file for '''!!'''). I use a batch file to renum and compile my NFO in one step.
*Don't worry about sprite numbers and lengths: NFOrenum will fix them up.
*Don't decompile your own grf files! You'll wreck your NFO, stripping out all formatting and comments.
[[category:NFO]]

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GRF coding