CGALIB and Composite Monitors

Monday, 13th July 2020

Many old games intended for the North American market supported CGA composite mode. This uses the colour artefacts generated by NTSC televisions and monitors to show more colours than intended by the hardware designer. While officially using a 640x200 2-colour or 320x200 4-colour graphics mode, games would use this colour artefacting to produce a display that appeared to give 16 colours at a 160x200 resolution.

The graphics functions of CGALIB assume a 320x200 screen and four colours. But with careful design of game assets, it's possible to create a game that shows 16 colours in composite mode. This is how it was normally done; I don't know of any graphics library that specifically treats the composite screen as a 160x200 16 colour mode.

While it would be possible to write such a library, and thus make 16-colour graphics easier, I'm not particularly interested in doing so myself. Here in Europe and many other parts of the world, where PAL was the dominant video standard instead of NTSC, the colour artefact technique doesn't work: PAL systems would display either in black and white, or at least in a closer approximation of the four colours the video hardware designers intended. As far as I know, it's not possible to design a single graphics set that looks good in both RGB and composite modes. So for my own efforts I'll be concentrating on getting the best out of the 4-colour RGB display.