VGA Innacuracies

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Joined: Thu 31 Aug, 2017 11:56 am

VGA Innacuracies

Post by mysoft » Thu 31 Aug, 2017 12:31 pm

so, i'm working on a "Gameboy Emulator" for DOS... running over TEXT mode.... ... sp=sharing

the test demo works on PCEm except that unlike on the PC's i have been testing, i have the following issues

1) the hsync palette swap "old" color method is inverted... (mismatching scanline count, actual scanline?)
i don't have any real PC doing that, but if so, i can just add a "swap colors" option...

2) if you enable the odd/even scanline bit (New Color option on the demo) that is used on CGA modes, but while in text mode
as the CRTC Mode Control Register (Index 17h) bit 0, suggests... and as happens on all notebooks / PC's / (many <= 486) etc... that i have tested, this does show even scanlines from offset 0, and even scanlines from 8192...
meaning i can just use different color attributes for each odd/even scanline, which does the 4 color effect i need :)
but that isnt emulated on PcEm (and that doesnt work on dosbox either)
any plans on emulating that? :)

some possible reference images... (the one on the middle that is streched vertically is NTVDM on my pc... newest card... so it does a bit weird... and obviously under ntvdm the "hsync palette swap wont work... so no 4 different shades there..."

on an unrelated note, everybody is free to test and give feedback / sshots about how it works there (on real DOS machines ^^)

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