Pinocchio - Trembling HUD glitch

[a-barone]

S32X Core version:
Release 20220607

Hi!

The Pinocchio prototype exhibits a trembling HUD when horizontally scrolling the screen only on the S32X core; it doesn't happen on real hardware. The videos I recorded were with the game running at 60Hz but the issue also occurs at 50Hz with the S32X core.
I recorded footage of the S32X core running side-by-side with a real Genesis 32X setup:
Real Hardware (Left) | S32X Core (Right)
https://youtu.be/PLxr75SaaKY

And here is a recording focused only on the S32X Core and zoomed in:
https://youtu.be/P669gY9YvLk

I used this ROM for the tests:
https://hiddenpalace.org/Pinocchio_32x_(Dec_6,_1995_prototype)

[asturur]

Issue still present in #45

[asturur]

if someone wants to try again
https://github.com/MiSTer-unstable-nightlies/S32X_MiSTer/releases/download/unstable-builds/S32X_unstable_20230415_072c29.rbf

[asturur]

To trigger the issue: Hud ( pinocchio life count ) tremble when scroll speed accelerate or decelerate, at any point in the game. Very visible at game start too.

[asturur]

tried, still there.
Just as a log, the issue is so minor that not sure anyone care.
Also probably the last active reported issue

[Toryalai1]

Is this still the case with the latest unstable?

[asturur]

I didn't manage to try the latest myself, today i need to solve the merge conflicts with latest master and i ll give a spin

[a-barone]

This issue still occurs both in the most recent stable release and in the unstable build from September.

[asturur]

Yeah this is the issue i try every update. Still there

[asturur]

with the nov build of 52df005 still there.

I start to wonder if is something tied to the MD/32X graphic sync since it happens only on acceleration/deceleration of pinocchio

[srg320]

I start to wonder if is something tied to the MD/32X graphic sync since it happens only on acceleration/deceleration of pinocchio

The problem occurs when the screen scrolls smoothly (1 pixel per frame). The game uses VDP 32X mode 1 (Packed pixel mode), where the SFT register is used for accurate scrolling by one pixel. I decompiled and explored the game code that responds to the scrolling. The rough scroll value for HUD is always constant. The accurate scroll is set once and for the entire frame, that is for the HUD too. Therefore, when scrolling by 1 pixel (change the SFT bit), the HUD trembles by one pixel. For example, the screen scrolls smoothly by values ...,48,49,50,51,52,53,... , then the HUD scrolls by values ...,0,1,0,1,0,1,....
According to the behavior of the game code and the VDP documentation this is the "correct" behavior in the game. The same problem is present in emulators. But in the original everything works correctly. I think there is some undocumented behavior of VDP 32X mode 1.