One of the big problems OpenGL runs into after you’ve got your first few polygons flying around the screen is the lack of a standard method for generating text within the API.
A few techniques have evolved to tackle the problem:
Pre-generated string textures
The simplest and fastest method, a texture is pre-built for each piece of text that needs to be displayed. This is quick to render at run time, but isn’t very flexible or efficient.
Polygon glyphs created from outline font definitions
This method produces high quality, scalable text, but this is also the slowest approach due to the overhead of generating and rendering the glyph polygons.
WGL and GLUT extensions
These extensions do a great job of text rendering. However, these libraries are not universally available on all systems and I have a bad habit of trying to be portable and platform independent.
Bitmap fonts are fast, flexible and platform independent. However, there are some limitations: Quality suffers when scaling up the texture and the number of possible characters in a font bitmap is limited. Extended or Unicode character sets with accents or non-latin symbols are not well supported.A bitmapped font is simply an atlas texture containing a collection of glyphs and symbols. The grid layout means that the calculation required to select any given character is quick and simple.
The area containing the selected characters can then be mapped onto a series of polygons to create dynamic strings of text.
Adding width information to the glyphs allows the textured quads to be overlapped to create better looking text with variable character widths.
There are quite a few bitmap font generators around, but one provided all the features I wanted. So I wrote my own.
Codehead’s Bitmap Font Generator (CBFG) is now at version 1.43 and supports the following features:
- DIB rendering of font gives best font output, regardless of users screen settings
- Global or per character position and width adjustment
- Texture Sizes from 16×16 up to 4096×4096
- Zoom up to 400% for accurate tweaking of character positions
- Anti-aliasing or ClearType (XP+) for smoother looking fonts
- Control of font width
- Font preview option
- TGA export option
- BMP output option
- BFF output in 8, 24 and 32bit colour depths
- C++ example source code for loading and rendering BFF files
- Binary font data export
- Font info dump option
- User configurable colours and startup parameters
Many people have made useful suggestions that have been implemented in CBFG, and the tool has been used on the following projects:
- Spaced Out 3
- TouchRoids (Android game, under development)
- Frank’s DIY MP3 Player
- Zauropod’s Bitmap to LCD converter
- ByVac’s BV4629 Touchscreen LCD
- SkaPong by Einar
- Beginning Android Games An APress book by Robert Green and Mario Zechner
BFF Loading Code
C/C++ – included in zip/installer.
Android by Codehead
CBFG hasn’t been in active development for a few years now, but there are still a few features I’d like to add:
- State save option
- Merge/Extract font image
- Export in other font generator formats
- Edit font image
- Unicode support
Cleartype system setting can overrides antialias settings in application.