font_spec

Homeworld Font Format Specification:

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The Homeworld font format will be optimised for 3D graphics systems which use direct color. To that end, the fonts will be composed as a single 2D texture with u/v coordinates for the individual font characters. Since many graphics systems impose limitations on the possible dimensions of textures, we will have to be able to specify the dimensions of this texture. For example, they may be the most efficient exponent of 2.

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The fonts will be stored in the file with a palette. Because the sizes of fonts is rather negligible compared to most other graphics, we will use 8 bit per pixel. The palette will have color information if the bitmap is a color bitmap, and alpha information if the font has anti-aliased edges or is transparent.

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The font file will have 5 main sections arranged in the following order:

• Header. This will contain information about the font and how it will appear

• Character map (actually part of the header). This will be a list of pointer to the individual characters. Unused characters will be NULL. This list will be 256 pointers.

• Character header information. This will be the u/v coordinates and size of the character.

• Character image. This will be the 8-bit bitmap with all the font characters crammed in.

• Palette. This will be the palette of colors and alpha for the following character image

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Following is a more detailed description of the individual sections.

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Header/Character map:

Name

Type and length

Usage

Ident. string

8 bytes

Compared to “Orannge” to verify this is a font file.

Version

16-bit word

Low byte minor version number high byte major version number.

Flags

16-bit word

Flags for the font*.

Ncharacters

32-bit word

Number of characters in file.

Spacing

32-bit word

Spacing between characters in this font.

Height

32-bit word

Full height of font (from top of tallest character bottom of lowest hanging character).

Ybaseline

32-bit word

Pixels from top of font to baseline of font (not full height if hanging characters).

Name

32-bit offset

Fixed up to optional name pointer.

Widthimage

32-bit word

Width of the full font image.

Heightimage

32-bit word

Height of the font image.

Ncolors

32-bit word

Number of colors in the font. Must be at least 2.

Ppalette

32-bit offset

Fixed up to a pointer to the palette.

Pimage

32-bit offset

Fixed up to a pointer to the font image.

reserved

16 bytes

Reserved for future font formats.

Characters

256 32-bit character offsets

Offsets (fixed up to pointers) to characters for each font. A NULL pointer means character not represented. The first entry is always NULL

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* Bit-field flags for the font file header:

• Color font. Monochrome is the default

• Alpha enable. By default, no anti-aliasing will be applied to fonts.

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Character headers:

There will be between zero and 255 character headers for a font. Each header will have the following format:

Name

Type and Length

Usage

u

16-bit word (pixel coords)

Left extreme of character image in font image.

v

16-bit word (pixel coords)

Top extreme of character.

width

16-bit word

Width of this character.

height

16-bit word

Height of this character.

OffsetX

16-bit word (screen coords)

x offset of bitmap on screen.*

Offsety

16-bit word (screen coords)

y offset of bitmap on screen.*

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* The offset values are to permit efficient packing of characters such as comma and lower-case ‘o’ which would not take nearly the full extent of the maximum character height. This will reduce the size of our fonts at a minimum of additional run-time expense.

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Character image:

This will be an 8-bit image of a width and height defined in the file header. It will index the palette which follows.

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Palette:

The palette will be a list of 32-bit RGBA values. There will be Ncolors entries in this list. This will describe the colors and transparency of the characters, if it is a color font or just the transparency, if it is a monochrome font. The simplest palette will be 2 colors : (0, 0, 0, 0) for the first (transparent) color and (0, 0, 0, 1) for the second (solid) color. The color for a monochrome font needn’t be specified here, as it comes from the function calls which render it. There will be a maximum of 256 colors.