NMLTutorial/Graphic files

NML Tutorial

Installation

Graphics files

Language files

NML Syntax

Starting an NML file (grf block)

• Creating a road vehicle

Item blocks

• • Item definition

Spriteset & spritegroup blocks

• • Adding the graphics

Template blocks

• • Templating the graphics

Cargotable block

• • Cargo-dependent graphics

Callbacks and switch blocks

• Creating a tram

• • Make it articulated

• • Adding the graphics

• • Fix the purchase menu

• Creating a train

Railtypetable block

• • Single engine

• • Three part articulated

• • Four part refit

GRF Parameters

• • Real life recolour scheme

• Creating an object

Spritelayout blocks

• • Adding the graphics

Version checks

• • Objects on slopes

32 bit sprites

• Adding 32 bit sprites

Base graphics replacement

• 32 bit base graphics

Conclusion

Glossary

NML Documentation

You can use any graphics file format as long as it's supported by the Python Image Library and as long the graphics file has one of the TTD palettes applied.

What image files should I use?

If you're unsure about what file format to use, take PNG as a safe bet. It can work with palettes and has the added advantage that it can be viewed by browsers and as such you can just upload your sprite files to the forums if you want to show them. PNG files are also widely supported by graphics editors.

What's this palette business?

Graphics for TTD can only use a limited set of colours (OpenTTD 32bpp graphics are an exception to this; while NML can handle these for you, it is not covered in this tutorial). Check the NewGRF Specs for what these palettes are and which colours are available to use. The DOS palette has a few more colours, so if you're still in the position to choose, go for that.

In theory you can draw in full-colour and then convert your result to the TTD palette, but that usually doesn't work out too well. It's best to only use the colours from the palette in the first place. Each sprite should get a blue background, for which you use the blue from index 0 (indicated as "Transparent" on the page of the link above, or hex colour #0000FF).

Make sure to actually save the graphics files with a palette applied, or NML will complain that you don't have one. If you don't have this palette, you can extract it from any decoded grf file or download a premade palette file.

Using palettes

This section covers how to apply a palette to a graphics file in several graphics editor. If you're editor is not listed here and you know how to work with palettes using it, please add it here.

Adobe Photoshop

In this subsection it is explained how to create a palette file and how to apply it using Adobe Photoshop (CS5 is used here, but identical or similar procedures apply in other versions of Photoshop). It is assumed that you have a clue about working with Photoshop.

Retreiving a palette file

You can use an existing graphics file that has the correct palette applied to retrieve the palette and save it to a separate file. This palette can then be applied to graphics files that don't have a palette. You can skip this part if you have downloaded a premade palette file.

1. Open a graphics file of which you know it has the correct palette in Photoshop. Decoded NewGRFs (using GRFCodec) surely will have the correct palette applied.
2. Go to Image > Mode > Color Table... The window from Fig. 1 will appear.
   

   Fig. 1: Photoshop palette window showing in this case the Windows palette
3. Click Save... and store the palette file (*.act) somewhere on your computer.

Applying a palette from file

The Windows or DOS TTD palette must be applied to your graphics file for them to work in GRFCodec and NML. For the next steps we assume that you have a palette file (*.act) with the palette of your choice stored somewhere on your computer.

1. Open a graphics file in Photoshop.
2. Go to Image > Mode and check if RGB Color is checked. Select it if that is not the case, which will convert your graphics file to full-colour, maintaining the colours as they appear.
3. Go to Image > Mode > Indexed Color... The window from Fig. 2 will appear.
   

   Fig. 2: Photoshop indexed color window
4. From the Palette drop-down, select Custom... The palette window (see Fig. 1) appears.
5. Click Load... and browse the palette file. Click OK to close the palette window.
6. In the indexed color window, you may select your choise of Dither. The dither will convert all colours that are in the graphics file but not in the palette to the palette colours. Either use the Diffusion dither (with preserving exact colors) or the Noise dither. Play around with the settings using the Preview to see the result and pick whatever looks best. If the sprites in the image file were drawn properly (using only palette colours), you should see no difference.
7. Click OK to apply the palette file (and dither) to this image file. Note that this will flatten all layers (if any) in your graphics file.
8. Save the file as (preferrably) a PNG image.

Important note on PCX files in Photoshop

Photoshop has a quirk in which palettes from PCX files are read and written backwards. This is no problem is you stay with pcx, but it is if you convert from pcx to png (and the other way round). Any such conversion will have the palette stored backwards in the target file, making it unusable by GRFCodec or NML. Note:

• You cannot use the palette file saved from a PCX file for a PNG file;
• You cannot use the palette file saved from a PNG file for a PCX file;
• When converting PCX <-> PNG, you must convert to RGB Color first and then back to Indexed Color, applying the palette file of your target file format (e.g. when converting to PNG, apply the palette retrieved from a PNG file).

GIMP

To be added.

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