Shot97 wrote: ↑Mon Apr 25, 2022 1:27 pm
You noted how DOS doubled the lines from 320x200 to 320x400 on a VGA monitor.
CGA and EGA monitors, just like Commodore monitors, used 15 kHz line frequencies. That means single-scanned scanlines in all supported resolutions.
When VGA was introduced, IBM could have supported both 15 kHz and 31 kHz line frequencies, but decided to reduce cost and only support 31 kHz. Backwards compatibility with CGA and EGA screen modes was achieved by simply doubling the vertical resolution, so the 320x200 15 kHz modes became literally 320x400 at 31 kHz. From the point of view of the monitor, "real" 640x400 and 320x200 VGA modes are indistinguishable at the analog signal level.
See the discussion here:
https://www.vogons.org/viewtopic.php?t=50069
Btw, in the second instalment of my article series I will tackle IBM PC compatibles, so EGA, VGA, and so on. You'll might find it an interesting read.
Shot97 wrote: ↑Mon Apr 25, 2022 1:27 pm
It always made me wonder "what is it about the Amiga where both systems are using the exact same resolution but I MUST use at least 640x400 as well as thousands of colors (256 colors looked terrible as well) in order for this emulator to even approximate the look of the real thing?
While I haven't used the early DOS versions of UAE so I cannot make any statements about it, I *can* say with 100% certainty that I was more than a little disappointed at the apparent "blockiness" of 320x200 VGA compared to 320x200/256 Amiga graphics on a similarly sized 14" monitor. I did some pixel gfx in DPaint back in the day, and my images didn't quite look right on my new VGA PC, something was off. I finally understood the technical reasons for that only about a year ago; it's quite fascinating, really.
But most definitely, 320x200 line-doubled on a VGA adapter cannot faithfully simulate the non-line-doubled output of the Amiga. I'm guessing in the recommended 640x400 resolution they blanked every second line, which was a lot more faithful albeit a bit too sharp compared to a C= 1084S (VGA monitors had much higher resolution, there was far less "blending" between the scanlines).
Entirely subjectively, 640x480 with 256+ colours was the "cutoff point" for me where PCs had finally surpassed the graphics of the Amiga.
I wonder if a flicker-fixer would have the same effect on an Amiga, or maybe it would leave the low-res modes intact? Hmm, I guess it would line-double even at low-res, because the whole point was to be able to use cheap VGA monitors instead of expensive multi-sync ones, and VGA only supported 31 kHz.
Shot97 wrote: ↑Mon Apr 25, 2022 1:27 pm
It could be more behind that but it's a curious thing I remember, I could probably take some pics of it if anyone is interested in seeing it.
Yeah, I'd be interested to see that!