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32bpp and OpenTTD

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

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

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

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

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The Format

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----------

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

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

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

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

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

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format. Alpha-channel is fully supported.

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

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

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

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

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

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

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8bpp color remapped and converted to 32bpp.

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

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

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

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

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

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