SCUMM/Technical Reference/Charset resources
Introduction
Character sets define the fonts used by SCUMM to draw text, such as dialogue, on the screen.
V1/V2 charset format
The V1 and V2 font format is identical to that found in V3 games; the big difference is that in V1 and V2, the font is not stored in the game data files, but rather is hardcoded into the executable.
Therefore, ScummVM has to include fonts for the various versions of the two affected games (Maniac Mansion and Zak McKracken). The fonts differ depending on the localization of the game.
Currently, ScummVM includes fonts for english, french, german, italian and spanish game variants. It is not known whether there were other localizations, but if you encounter any make sure to tell the team about it!
V3 charset format
The header looks as follows:
| Size | Type | Description |
|---|---|---|
| 4 | unknown | |
| 1 | byte | number of characters |
| 1 | byte | height of the font |
| 6 | bytes | character width table (one byte for every char) |
After this header the character data starts. Every character in the charset takes up exactly 8 bytes, representing 8x8 pixels in which the actual character is contained (the actual width and height of the char should be computed from the charset header).
V4 charset format
The header looks as follows:
| Size | Type | Description |
|---|---|---|
| 2 | unknown | |
| 15 | bytes | colour map |
| 1 | byte | number of bits per pixel |
| 1 | byte | height of the font |
| 2 | short (LE) | number of characters |
| 1024 | 256*quad LE | character data offsets |
Character glyphs may be 1, 2, 4 or 8 bits per pixel, and can be masked.
The colour map contains the colours each pixel of the character glyph is drawn as. Pixel value 0 is used for transparency; the other values are mapped using the color map in the header.
The character data pointers contain the offset, relative to the byte after the end of the colour map (byte 29), of the character data. This can be 0 if that particular character is not encoded in the character set. The character data itself is formatted as follows:
| Size | Type | Description |
|---|---|---|
| 1 | byte | width of character |
| 1 | byte | height of character |
| 1 | byte | X offset |
| 1 | byte | Y offset |
| many | bytes... | glyph data bitstream |
The X and Y offsets are added to the screen coordinates of the top-left corner of the glyph before drawing. This is useful for, say, shadowed text. Needless to say, glyphs don't all have to be the same size, although in all the examples I have they are the same height.
The data bitstream encodes the pixels in the glyph in left-to-right, top-to-bottom order. Multiple pixels are encoded per byte. The pixels are arranged in big-endian format; so, the first pixel in the stream is in the top bits of the first data byte; then the bits below that; and so on. For example, at one bit per pixel:
Bit position: 7 0 7 0 ... Words of data: 01234567 89ABCDEF
At two bits per pixel:
Bit position: 7 0 7 0 ... Words of data: 00112233 44556677
And at four bits per pixel:
Bit position: 7 0 7 1 ... Words of data: 00001111 22223333
V5/V6 charset format
Like all other resources in V5 and later, the charset data is stored in a chunk, in this case a 'CHAR' chunk. The header looks as follows:
| Size | Type | Description |
|---|---|---|
| 8 | chunk tag | CHAR chunk tag |
| 4 | quad LE | size-23 |
| 2 | short | version ? (always 0x6303 in dott) |
| 15 | bytes | colour map |
| 1 | byte | number of bits per pixel |
| 1 | byte | height of the font |
| 2 | short (LE) | number of characters |
| nchar*4 | nchar*quad LE | character data offsets |
Observe that this header is identical to the V4 header with a few bytes added to the start of it. The charset format is otherwise identical to the V4 format described above.
NUT (V7 & V8) charset format
Header of NUT file
| Size | Type | Description |
|---|---|---|
| 4 | chunk tag | ANIM chunk tag |
| 4 | quad LE | size of ANIM chunk (AHDR and number FRME chunks included) |
| 4 | chunk tag | AHDR chunk tag |
| 4 | quad LE | size of AHDR chunk (datas until FRME chunk) |
| 2 | short LE | number of chars |
After AHDR chunk there is FRME chunk for per char of number chars:
| Size | Type | Description |
|---|---|---|
| 4 | chunk tag | FRME chunk tag |
| 4 | quad LE | size of FRME chunk (with whole FOBJ chunk too) |
| 4 | chunk tag | FOBJ chunk tag |
| 4 | quad LE | size of FOBJ chunk |
| 2 | short LE | id of codec (could be 1, 21, 44) |
| 2 | short LE | X display position of char |
| 2 | short LE | Y display position of char |
| 2 | short LE | width of char |
| 2 | short LE | height of char |
| 2 | short LE | unknown |
| 2 | short LE | unknown |
| unk | byte | font gfx data, size of data is rest of FRME size |