01852: fantzone, fantzone1: Graphical glitch of the background at the beginning of the game.

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
01852	Graphics	Minor	Always	May 31, 2008, 20:50	Sep 3, 2021, 17:14

Tester	Fujix	View Status	Public	Platform	MAME (Self-compiled)
Assigned To		Resolution	Open	OS
Status [?]	Confirmed			Driver	sega/segas16a.cpp
Version	0.125u3	Fixed in Version		Build	C2D
		Fixed in Git Commit		Github Pull Request #

Summary	01852: fantzone, fantzone1: Graphical glitch of the background at the beginning of the game.
Description	The background briefly gets corrupted when I start a game and get ready to play. This is a long existing "one-frame" issue but clearly a bug and never seen on the real arcade.
Steps To Reproduce
Additional Information
Github Commit

Flags	Verified with Original
Regression Version	0.88u7?
Affected Sets / Systems	fantzone, fantzone1

Attached Files	fanta.gif (165,717 bytes) May 31, 2008, 20:53

No.09127 moa Tester Dec 8, 2012, 22:29	looks fixed in 147u2
No.09134 Tafoid Administrator Dec 13, 2012, 23:45	Still happens here, tested with 0.147u3. You really can see if it you SHIFT+P (pause by frame) your way to it.
No.09143 Phil Bennett Developer Dec 18, 2012, 15:56	What's happening is the MSBs of the scroll registers are being overwritten mid-frame when the round starts by a routine which clears the text RAM (the scroll registers occupy the last few words of the RAM). The correct scroll values are restored during the following VBLANK. Adding VIDEO_UPDATE_AFTER_VBLANK will hide the glitch.
No.19222 hap Developer Sep 3, 2021, 15:27	It is just this single-frame glitch? Then VIDEO_UPDATE_AFTER_VBLANK (or an other hacky workaround) is not worth it.
No.19223 Haze Senior Tester Sep 3, 2021, 17:14	yeah, as I previously speculated I think maybe the hardware latches these scroll values at some point, but doing that was shot down when I suggested it.