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ID Category [?] Severity [?] Reproducibility Date Submitted Last Update
06705 Graphics Major Always 8 days ago 6 days ago
Tester MrGW View Status Public Platform MAME (Official Binary)
Assigned To Resolution Open OS Linux (64-bit)
Status [?] Confirmed Driver coco3.cpp
Version 0.190 Fixed in Version Build 64-bit
Summary MESS-specific 06705: coco3 [megabug]: Graphic corruption when running MegaBug using the Coco 3 driver
Description William Schaub discovered a graphic corruption issue when playing MegaBug on the Coco 3. It loads as a "split screen" where the top half is the entire game with slight corruption at the very bottom. The bottom half is a duplicate copy of the top half with the exception that the bottom half screen will change back and forth from a copy of the top half to complete graphic corruption. This happens whether you are moving your player character or not.

This behavior is exhibited when loading the game as a CART, DSK image or CASSETTE image.

The game works correctly when using the Coco 2 drivers.
Steps To Reproduce Start MAME with the following command line:

mame coco3 -nomouse -window -debug

Insert the Megabug rompak (CART) using MAME's built-in UI.
Additional Information William was able to find a workaround (with a rather interesting palette) by entering b@ff22=CD in the debugger window.

The same issue happens when trying this on the official MAME binary for Windows (William has Windows v8.1).
Flags
Regression Version
Affected Sets / Systems coco3 [megabug]
Attached Files
jpg file icon megabug-issue.jpg (109,693 bytes) 8 days ago Uploaded by MrGW
Screenshot of issue
MrGW
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Notes
4
User avatar
No.14245
MrGW
Tester
8 days ago
Rick Adams has confirmed he sees this same behavior with the Temple of ROM game cart. Rick is the original author of the game.
User avatar
No.14246
Tafoid
Administrator
8 days ago
So, you are stating that megabug doesn't work on original hardware coco3? I have both but my set up is long packed away so I can't test readily.
User avatar
No.14247
MrGW
Tester
8 days ago
Hi Tafoid. Let me clarify by saying that Rick sees this same issue when running his game in MAME. Both games work correctly on real Coco 3 hardware.
User avatar
No.14264
MrGW
Tester
6 days ago
Steve Bjork wanted me to forward his comments for this issue:
"Have the guys working on the bug in mane look at the Sam/VDG mode system. From that I can see in the pictures, the game is trying to display a 3k screen, but MAME is doing it as a 6k screen. Easy for 1/2 coco but hard for the CoCo 3 graphics system. Mega-Bug did not work on the first designs of the Gime for the CoCo 3."

As an FYI, Steve is the original author of MegaBug.