08576: gameboy and clones, gbcolor and clones: Screen tearing even with waitvsync active

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
08576	Graphics	Minor	Always	Mar 2, 2023, 21:57	Mar 3, 2023, 13:58

Tester	ICEknight	View Status	Public	Platform	MAME (Official Binary)
Assigned To		Resolution	Open	OS	Windows 10/11 (64-bit)
Status [?]	Confirmed			Driver	nintendo/gb.cpp
Version	0.252	Fixed in Version		Build	64-bit
		Fixed in Git Commit		Github Pull Request #

Summary	08576: gameboy and clones, gbcolor and clones: Screen tearing even with waitvsync active
Description	There seems to be some unavoidable screen tearing going on with both the Game Boy and Game Boy Color emulation (including "Super Game Boy").
Steps To Reproduce	-Load the Game Boy driver. -Load sml2. -Wait for the demo to play or just start a new game. Notice the wobbly tearing going on.
Additional Information	Different games and different drivers seem to give slightly different results, such as the tearing line being static or not, and a different height for it.
Github Commit

Flags
Regression Version
Affected Sets / Systems	gameboy and clones, gbcolor and clones

Attached Files	sml2.png (4,072 bytes) Mar 2, 2023, 21:57 Uploaded by ICEknight gbcolor sml2
Attached Files	sml.png (2,574 bytes) Mar 2, 2023, 21:57 Uploaded by ICEknight gameboy sml

No.21134 Robbbert Moderator Mar 3, 2023, 09:18	Confirmed. On gameboy it's more obvious, because there's an odd ripple effect scrolling downwards, and the displacements occur where this effect rolls over. This is regardless of -waitvsync being used or not.
No.21135 Haze Senior Tester Mar 3, 2023, 10:50 edited on: Mar 3, 2023, 10:50	is this confirmed to not happen on hardware? remember, original games can have tearing too
No.21136 cuavas Administrator Mar 3, 2023, 13:58	It’s because the Game Boy VDP classes run completely independently of the screen device. The VDP’s vertical timings are detached from the screen device’s vertical timings. I don’t get a ripple effect scrolling down in games like Super Mario Land – the tear sits at the same place for an entire session. There are far bigger issues with the CGB VDP anyway, and the code is pretty old. It could probably do with a rewrite.