The graphics system in Simutrans is based on tiles, in order for an image to be displayed correctly in-game, the source image needs to be divided into tiles depending on their intended position. Each tile is a square area with the following dimensions:
|Pakset size||Width in pixel||Height in pixel|
A building consists of ground-level tiles (blue) and up to 3 height-level tiles for each ground-level tile (red - 1 height).|
The parts of the ground-level tile shown in green in the image to the right will not be visible in-game.
A building which only consists of a single ground-level tile does not need to be cut. Only when a building is made up from several ground-level tile is it necessary to cut the graphics.
The information in the graphics file correspond to the values of [B] [C] [D] of the BackImage parameter. Their relative ordering from top to bottom is given vertically.
other sizes can be found here
To help cut up an image according to these specifications, there is a Windows-program called TileCutter (German description only); under Linux TileCutter works well with Wine.
It will take 2x the original graphics, a target file and the appropriate interface mask.
The next step is to mask the intersection of the two original images; with red and blue respectively being used as transparent.
Then the partial images are copied into the target file.
Finally, the red and blue of the mask as well as the tile backgrounds of the target file are filled with transparent color. The original image is also copied into the target file.
It is a very good idea to add a copyright notice to the target file. Then everyone knows by whom the picture is, even if the file name changes.