Okay, i've been pondering about this for quite some time, and I can't get it out of my head for any real length of time, so I suppose I have to announce that I plan on creating a Apple II/IIGS VGA card. My background is that of a Java/C++ developer with hardware background, however I am a vintage Apple/Macintosh collector/fan. I have a bunch of old macs, and my special IIGS with a CFFA card. This CFFA card is what started my quest to make a VGA card. I'm starting to see who else would be interested in working on this as a collaborative project as an open-source "give back to the community" type of thing. Here's what I already know:
The IIGS supports all of the 320x240 display modes, plus 640x200 graphics mode. The video memory on a IIGS resides as a special bank of memory, buffered/copied to one of the upper banks of memory (from the original locations on a II).
I have began to experiment with arduinos and teaching myself AVR assembly. This card will ONLY work with either a Arduino Due or a FPGA type solution (I'm leaning toward FPGAs). I'm not sure *which* FPGA I should go with, but Rich picked the Spartan 3 and sparkfun has a dev/breakout board for that particular FPGA.
Starting off, I want to take the RGB video stream from the IIGS, and double each pixel (to 640x480) and create a VGA data stream with a wierd looking IIGS display. Once that works, I move onto centering the image with the blackground color "filling in" the spaces that video isn't residing in, and finally making the card internal, reading directly from memory using DMA and writing a GS/OS control / desk accessory that will allow GS/OS to make use of the higher resolution directly.
This has all been done before with the SecondSight VGA card, however I don't have one of these cards, nor the funds to procure one of these doo-dads off of ebay. So I'll have to re-invent this, but from what others have told me in the past, FPGAs should be able to do this, and I have a feeling I can get some help with the VHDL/Verilog code necessary for this to work out.
I also have a CFFA card which implements a desk accessory, so I might be able to learn something from that too (doubtful).