Possible overscan regression
johnnovak opened this issue · 9 comments
Not sure if this change in behaviour is more or less accurate or intentional, but I thought it's best if I report it.
5.2.0 beta 7
A500, Kick 1.3, NTSC, OCS, Overscan mode
The bottom scanline in the Workbench screen is incomplete and the last few pixels are flickering.
If I switch to ECS Agnus, there's one less scanline, so the glitch is hidden. The flickering in particular is slightly annoying.
5.2.0 beta 4
Same config, with OCS the extra scanline is shown in Overscan mode, but it's a complete line and there is no flicker.
This is how the incomplete last scanline looks like in beta 7 with NTSC + OSC + Overscan:
Config file required, can't duplicate it like in your screenshot. Partial top and bottom lines are correct (It is OCS Denise "feature", vblank starts/ends at zero horizontal position which is visible. Most normal TVs back in the day don't show that much overscan) but they should be only visible if mode is Overscan+ or higher. (Because they look like emulation bug..)
You should be able to reproduce it with this config right at the boot screen:
Overscan Test.zip
The config has OCS + NTSC, but I found another bug when you switch to PAL and leave all other settings untouched (see screenshots below; in PAL mode there's a glitch at the end of the top row).
I think this is the partial top/bottom line OCS "feature" you mentioned, but yeah, seems like a bug to non-experts 😄
As mentioned, switching to any other chipset than OCS "fixes" it.
OCS / NTSC
OCS / PAL
Just tested this with beta 8, but the issue is still there using the repro pack from the above post. It's exactly the same behaviour, no improvement.
Yeah, it's pretty annoying when watching PAL OCS demos too. Can you please fix @tonioni? (Switching to ECS Agnus "fixes" it, but that's not a proper fix...)
Config & disk image attached.
Megademo (Alcatraz, 1988).zip
Alcatraz-Megademo1.zip
Blank lines on top and bottom right: these are now disabled unless overscan mode is overscan+ or higher. (These blank lines are not emulation bug, they really do happen with OCS Denise and are visible on most normal displays as long as it shows full overscan. And they do flicker if NTSC because NTSC line length alternates)
Demo: I can only see short blue line in bottom right corner which is correct behavior. I can't duplicate long blue line except by enabling Overscan+ mode which shows all visible lines (same as real A500 + OSSC can show when OSSC is configured to show everything possible). Do you have any centering options enabled? If yes, does it happen without it? (I guess I'll need to completely disable last possible visible line unless overscan+ because almost no normal display device can show it)
Yes, the long blue line only shows with vertical centering enabled. If that's disabled, I only get a very short blue line in the bottom right corner.
Vertical & horizontal centering is enabled in my attached config, by the way—if you use that, you should get the same results in beta 8.
IMO it's fine to chop off a few more lines to make sure none of the flickering and incomplete line artifacts show up with any setting combinations in normal Overscan mode. It's not as if there was a strict standard on the exact overscan size in monitors/TVs, and you adjusted the horiz/vert stretch controls on monitors anyway until things looked good. No one would have adjusted it so to see visible flicker or extra bright lines (full or partial) at the top or bottom in black background games or demos.
Most things work as expected with beta 9, no weird flickering extra lines anymore.
NTSC + Overscan has been restored to how it was before, that's good too.
The Alcatraz Megademo is still affected but probably it's a weird outlier, so no big deal. I'll raise this again if I come across more weirdness with Overscan, but probably we can close the issue ticket for now.
I added one more overscan/overscan+ difference: do not show last almost always hidden line if not overscan+ or larger. This is basically same behavior as pre-4.9 which didn't have any support for line "wrap around" (where bottom last line is actually line 0 or 1 depending on config, or even larger if programmed mode)