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Ultima > I Mondain > Development > Global Map Tile Type

EGA Global Tiles Data Type

   The surface map uses tiles from the global tile file (EGATILES.BIN). It has a fixed length of 6,656 bytes long. Tiles are 16x16 pixels. EGA formatting of each tile makes a tile size 128 bytes. This figures out to 52 tiles in the file. 

   EGA formatting assigns four bits to each pixel (16 colors in EGA, this link shows them) but the bits are not contiguous. Bits are grouped in 16 bit words, one for each of 16 pixels in a line of the tile. The first word is the least significant bits (LSBs) of the EGA color table index. The next word's bits are the second order followed by a word containing the third order bits. The final two bytes are the word containing the most significant bits (MSBs) of the index. In this manner, each group of eight bites forms one scan-line of pixels in each tile.

The list of global tiles can be viewed here.