BM Files

BM Files General

BM files contain bitmaps for such things as the game status displays, main screen backgrounds, force and item icons. They may or may not contain mulitple images, palettes, and may be 8-bit or 16-bit images.

The BM file is structured in two parts with a possible third for 8-bit BMs.

File structure: TBMHeader TImages TPalette // the palette is only present in some 8-bit files (Bk*.bm)

The header for a BM file is:

Notes:

If a palette isn't included, PalInc should be set to 1. It is set to 0 in a few of the 8-bit images, but setting it to 0 causes strange effects with some 16-bit BMs.

X and Y offsets have their origin in the top-left corner of the BM being overlaid

With 8-bit images, Transparent is an index into the palette. With 16-bit images, Transparent is a 16-bit RGB value.

Uk4 and Uk5 seem to control the ratio between different colours. It is unknown exactly how.

Next follows Image data

First Image always at offset 0x80 (128). TImage=record SizeX : Longint; // Image horizontal size in pixels SizeY : Longint; // Image vertical size in pixels Data : Array[SizeX * SizeY] of byte; // Image data for 8-bit image or Array[SizeX * SizeY] of word; // Image data for 16-bit image end; Note: Repeated for the number of entrys in NumImages of header

The image data starts with the pixel in the top-left corner of the image, and defines pixels in rows going downwards. For 8-bit images, each byte in the Data array is an index into the palette. For 16-bit images, each word contains the RGB values for a pixel, where the least significant 5 bits are the blue intensity, followed by 6 bits for green intensity, and the most significant 5 bits are the red intensity.

Followed by the optional palette information if BM is 8-bit, and PalInc = "2" in header.

TPalette=array[0..255] of record r, g, b : byte; end;