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ID Category [?] Severity [?] Reproducibility Date Submitted Last Update
08334 Graphics Minor Always May 29, 2022, 22:59 31 days ago
Tester kmg View Status Public Platform MAME (Self-compiled)
Assigned To Resolution Bugs That Aren't Bugs OS MacOS X
Status [?] Resolved Driver a2600.cpp
Version 0.244 Fixed in Version Build 64-bit
Fixed in Git Commit Github Pull Request #
Summary MESS-specific 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
Regression Version
Affected Sets / Systems a2600 [astrblst and clones]
Attached Files
png file icon astrblst.png (1,075 bytes) May 29, 2022, 22:59 Uploaded by kmg
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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
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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.
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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.
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31 days ago
Yep, typical Atari quirkiness. Jr. Pac-Man is notoriously bad for this too, the entire left side of the maze has lines through it.