An old-style graphics system as found on many 8-bit computers and on early PC graphics cards drew its characters by retrieving their bitmaps from a ROM. With a little sideways thinking, [GloriousCow] has exploited this process to make a CGA card perform graphical tricks it was never designed to do.
The CGA card clocks its character ROM continuously across the whole screen, even at the edges where nothing would normally be displayed. By placing the ROM in tandem with a Raspberry Pi Pico 2 they were able to use this ROM clocking as a synchronization signal, and inject whatever pixel data they chose.
The result is a CGA card that can display 60 Hz high-res graphics in text mode, albeit with a very retro one bit color depth. It can overlay the text and the graphics too, because the ROM is still present. One fun result of this is a bouncing DVD logo screensaver, on a DOS PC.
There’s a PCB and a promise of more, meanwhile we suggest you take a look at an impossible feat using a similar technique: NES Doom.
In 2015, a retro demo scene crew put together an unimaginably good CGA demo: https://www.youtube.com/watch?v=yHXx3orN35Y
The seemingly impossible achievements that came out of the demo scene will never cease to be impressive.
Where there’s a will, there’s a way.
And loads of dithering.
Looks good on a Commodore 1702! :)
And that’s not even using Super CGA (ie Plantronics) yet! ;)
Who knows what’s possible with the other 6845 CRTCs (Hitachi HD46505, Fujitsu MB89321A, Yamaha V6355) ?
Fans do the best work
—RetroBlasting
It’s been 41 years since the introduction of the Amiga and the Boing! demo, and PC fans are still jealous of it…
Now to make the dvd logo bounce around the screen. Bets on when it hits the corner perfectly.
It does bounce. And it may even hit the corner :)
We’d built a complete text-based windowing system using character graphics with smooth scrolling via character set shifts; that was VGA/EVGA era, circa WfW 3.11 which pretty much killed That.