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Forums > C64 Coding > Right-most sideborder sprite bug
2006-09-06 17:38
JackAsser

Registered: Jun 2002
Posts: 1989
Right-most sideborder sprite bug

If you remove the sideborder and place any sprite at the very right most place in the border you will see about 8 pixels wide garbage on the line before the actual sprite (all 21 sprite lines are accounted for below this point). This is also some kind of sprite data and share the colors from the sprite that is about to be shown. VICE emulates it somewhat correct. This means that the sprite is actually 22 lines high?!

How and why does this occur and from where are the pixels fetched when the bug is outputed (or is it a bus-lock of some kind)?
 
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2006-09-06 21:33
Graham
Account closed

Registered: Dec 2002
Posts: 990
The garbage is always the same $00 $FF $00 pattern one line above the actual sprite data. The $00's are just what is left in the sprite data shift register, and the $FF is propably a result of the shift register receiving tristate mode while wanting to receive non existant data. Just an assumption though.
2006-09-07 02:05
Style

Registered: Jun 2004
Posts: 498
with my sideborder dysp I cheated and set the sprite colour to the background colour for the first row :)

edit: Graham, were early VIC-IIs tri-state? I read somewhere that 6581's arent.......

2006-09-07 04:49
JackAsser

Registered: Jun 2002
Posts: 1989
@graham: makes some kind of sence at least. ;)

@style: I have an old VIC-II chip with the old colors and cheramic casing etc.. The bug is visible there too.
2006-09-07 14:11
Krill

Registered: Apr 2002
Posts: 2850
Hmm, the only way to get rid of that ug is indeed setting the corresponding colour register to background.
2006-09-07 15:12
Graham
Account closed

Registered: Dec 2002
Posts: 990
You can also use X-position, or just move the sprite 1 pixel up... Or cover the bug with another sprite... or... or... or...
2006-09-07 19:23
Danzig

Registered: Jun 2002
Posts: 429
or pronounce a BUG as a FEATURE like some silly east-european visual-basic-coder did...
2006-09-07 19:58
MRT
Account closed

Registered: Sep 2005
Posts: 149
You mean, like opening up the borders? ;-)
2006-09-07 20:02
Danzig

Registered: Jun 2002
Posts: 429
no, i mean like creating recordset1, open NONE-EXISTING recordset2 and looping over recordset3... NOT WORKING :) ... and as i removed >>On Error Resume Next<< all these ERROR-Messages appeard and he claimed: its all FEATURES in the program.... but yeah, i ment bugs like opening the borders ;)
2006-09-07 20:13
Krill

Registered: Apr 2002
Posts: 2850
Graham: true. I should do some nifty sideborder code again, seems too much chunkyness and drive shit have paid their toll on me. :D
2006-09-08 01:17
Style

Registered: Jun 2004
Posts: 498
graham: moving the sprite 1 pixel up just moves the corrupt gfx 1 pixel up :D

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