08334: a2600 [astrblst and clones]: Black lines on left side of screen

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
08334	Graphics	Minor	Always	May 29, 2022, 22:59	Jun 2, 2022, 02:28

Tester	kmg	View Status	Public	Platform	MAME (Self-compiled)
Assigned To		Resolution	Bugs That Aren't Bugs	OS	MacOS X
Status [?]	Resolved			Driver	atari/a2600.cpp
Version	0.244	Fixed in Version		Build	64-bit
		Fixed in Git Commit		Github Pull Request #

Summary	08334: a2600 [astrblst and clones]: Black lines on left side of screen
Description	Objects coming down at player and shots going up are accompanied by black bars moving up/down the left side of the screen. This happens for all three sets including the PAL version. The top scanline also appears to be only partially drawn.
Steps To Reproduce	Easiest way to reproduce is to load game and switch Right Diff. Switch to 'A' in the DIP Switches menu. This will change the background to gray so the lines can be seen. (Otherwise you'll need to score 1000 points in 'B' mode.) Press P1 fire button to start. Glitched lines should appear immediately.
Additional Information
Github Commit

Flags
Regression Version
Affected Sets / Systems	a2600 [astrblst and clones]

Attached Files	astrblst.png (1,075 bytes) May 29, 2022, 22:59 Uploaded by kmg

No.20258 Tafoid Administrator May 29, 2022, 23:15	Those lines on the sides are common with Atari 2600 games, if memory serves correctly. This game has them on actual hardware recordings Time index 0:32 game starts
No.20259 kmg Senior Tester May 30, 2022, 00:04	Yeah sorry, it does look that way. I assumed they wouldn't have released it like this but I should have looked for hardware footage first. I'm really only familiar with the INTV original.
No.20260 CYBERYOGI -CO-Windler Viewer May 30, 2022, 04:14 edited on: May 30, 2022, 04:16	The VCS2600 console itself is full of glitches and oddities because it is programming on the metal without framebuffer. E.g. framerate can slightly differ among game levels and intermediate/title screens by varying count of scanlines, so on the 1970th Saba Ultracolor TV at my parents house either some games/levels roll up or others roll down depending on the current vsync trimmer setting inside the TV (which PLL sync range was smaller than in 1980th PAL TV sets). The programming of 2600 graphics has not scanline interrupts but basically is a single giant scanline interrupt routine (the way timing needs to be hand-tweaked by counting CPU cycles to place things on screen). Sprites are vertically reused in software; in the gaps between visible sprites they are often parked at zero (leftmost) position and switched to black, which produces the "comb" at the left screen edge. Some games try hard of hiding it, while others don't care or simply lack CPU time to do so.
No.20280 Heihachi_73 Tester Jun 2, 2022, 02:28	Yep, typical Atari quirkiness. Jr. Pac-Man is notoriously bad for this too, the entire left side of the maze has lines through it.