Only the upper part of the image is visible in Seven Seas by Andromeda with some very specific display settings

[johnnovak]

I ran into this problem in Seven Seas by Andromeda, and I couldn't reproduce it with anything else, which makes this a rather strange issue.

Please use the attached repro pack (config paths will need adjustments): seven-seas-repro-pack.zip

The problem only manifests with the following combination of settings as per the included config:

• Line mode: single
• Interlace mode: single
• Lagless VSync enabled
• Vertical centering: off

Changing any single setting of the above will "fix" the problem (e.g., using regular or no vsync, or double line mode, or enabling vertical centering).

Could reproduce in all 5.2.0 betas, 5.0.0, and 4.9.1.

Repro steps

1. Hold left mouse button at boot to go straight to the second part (image selection menu). Note only the upper part of the image is displayed.

2. Enable vertical centering -- now the whole image is displayed correctly. (You can "fix" it the same way by selecting normal vsync, disabling vsync, or changing line mode to double.)

3. Turn vertical centering off again -- now we're back to only the upper half being visible.

4. Load the first interlaced image (Zenith). Same problem.

5. Change the floppy in DF0: to Shadow of the Beast disk 1, soft reset, and watch the intro. It's perfect, including the interlaced HAM picture at the end. So Seven Seas must do something that confuses WinUAE, but probably it indicates a general problem.

Also tried the same settings in Workbench 1.3 and displayed a few images in various screen modes -- no issues, everything works as expected.

Screenshots

[johnnovak]

Issue still present in 5.2.0 beta 7.