Search for cga_comp

I showed four png screenshots taken from cvs (the ones that are not on video: both "textmode reprogramming" screens and both "start address reprogramming" scrollings) to Trixter and he said they all are OK.

That just leaves the missing border and cursors, unless someone has spotted other glitches besides thiese.

boarder is discussed here: VIDEO - Overscan border (SDL1)

In dosbox there are also no:
- snow effect
- interlaced video mode
Horizontal retrace detect is not done properly.

Although you will have to find a game that suffers from it first 😉

Trixter said Bob Winner uses Display Positioning for scrolling the screen although the game seems to work properly in dosbox (although the scrolling seems not to be perfect (simmilar to super zaxon a bit) but it is the same on ega and vga and on real hardware too)

According to Trixter, interlaced video modes on CGA hardware is broken, and why no programs have ever used it, so that can be ignored.

> Horizontal retrace detect is not done properly.

It's working here 😁 😉

ih8registrations wrote:

According to Trixter, interlaced video modes on CGA hardware is broken, and why no programs have ever used it, so that can be ignored.

it works on the video. And you cannot tell that no program ever used it, if you haven't checked all the programs 😉

h-a-l-9000 wrote:

> Horizontal retrace detect is not done properly.

It's working here 😁 😉

I wonder how it would look like together with a boarder patch.

I'm just relaying what Trixter wrote. Displaying isn''t the problem, it displays, it just doesn't interlace, the lines are overlapped, done together, or other, I forget the description exactly.

Trixter and I figured this out a while ago by looking at the CGA schematics. Interlaced mode works by making an odd number of half-scanlines per field and is theoretically supported by the 6845. However, the IBM CGA hardware manipulates the horizontal and vertical sync pulses that come out of the 6845 (in order to add the color burst signals) and synchronizes the vsync pulses to the hsync pulses, so while the interlaced mode does *something* on a genuine IBM CGA, it isn't particularly useful. You get the even scanlines in the even fields and the odd scanlines in the odd fields but the scanlines appear in the same places on the screen in both sets of fields.

Apparently a 400-line interlaced mode was possible on the AT&T 6300 though so presumably there is some software out there somewhere that was written for that card which does interlacing. There's some more information about this at http://www.vintage-computer.com/vcforum/showt … ?t=13722&page=6 (posts 54-65).

robertmo wrote:

Bob Winner uses Display Positioning for scrolling the screen

Bob Winner uses Start Address Reprogramming not Display Positioning 😜