32bpp and OpenTTD

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OpenTTD has 32bpp support. This means: OpenTTD still is 8bpp, but it has the

posibility to override the graphics with 32bpp. This means that it isn't a

replacement of grf or newgrf, but simply an addition. If you want to use 32bpp

graphics of a newgrf, you do need the newgrf itself too (with 8bpp graphics).





The Format

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32bpp images are stored in PNG. They should go in:

  data/sprites/<grfname>/<SpriteID>.png



For example, a grfname would be 'openttd' (without .grf, lowercase), and the

SpriteID 3, to override the 3rd sprite in openttd.grf with a 32bpp version.



The format of this PNG can be almost anything, but we advise to use RGBA

format. Alpha-channel is fully supported.



As the core of OpenTTD is 8bpp, and because you of course want company colours

in your images, you will need to add a mask for every sprite that needs colour

remapping. The name is simular as above, only you have to put a 'm' behind the

SpriteID. This image should be a 8bpp palette image, where the palette is the

OpenTTD palette. Upon load of the PNG, the mask is loaded too, and overrides

the RGB (not the Alpha) of the original PNG image, and replacing it with a

8bpp color remapped and converted to 32bpp.



An other thing that OpenTTD needs in your png, is 2 tEXt chunks: x_offs and

y_offs. This to define the x- and y-offset, of course. Use the tool we supply

to add this information. Sadly enough most graphical editors trashes those

chunks upon save, so you have to readd it every time you save your image.



Your images should be the same as the grf, in size.



