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Forums > C64 Coding > FLI Bug
2006-04-18 13:45
MRT
Account closed

Registered: Sep 2005
Posts: 149
FLI Bug

I came across the following situation:

Set the VIC to character mode and multicolor.
Now generate a badline every rasterline and changing $d018 so that the VIC fetches data from a new screen (Video Matrix Base Address) every rasterline...

In this situation the FLI bug only completely appears when the last eight bytes of the charset (the last char in the charset) are filled with $ff.
So, when you fill those bytes with $00, you won't see the FLI bug and the background color is shown.
And no need to mask the bug with sprites anymore!

Even if you draw a smiley in the last char, the FLI bug shows only those smileys!

Now, my questions...
1. Are my findings correct? Or is there more to it?
2. (How) Can this be done in bitmap mode?

I've only tested this on Vice and CCS, it may differ on a real C64
2006-04-18 14:13
JackAsser

Registered: Jun 2002
Posts: 1909
* Char mode (single color):
Graphics from the $ff char.
Bg-color from $d021
Fg-color from the value of the op-code following the $d011 write.

* Char mode (multi color):
Graphics from the $ff char.
Bg-color from $d021
$d8xx color from the value of the next op-code
Other two MC-colors are normal.

* Bitmap (single color):
Normal bitmap graphics
Colors from $ff == gray+gray

* Bitmap (multi color):
Normal bitmap graphics
Bg-color from $d021
$d8xx color from the value of the next op-code
screen colors from $ff == gray+gray

(I THINK!) :D
2006-04-18 14:28
Cruzer

Registered: Dec 2001
Posts: 1002
@MRT: Your findings seem correct to me. If you wanna hide the bug in bitmap mode, w/o using sprites you can just clear all pixels in the bug area if it's multicolor mode. In single color mode the bug will always be light gray, so a popular way of disguising this is to make the border and "background color" of the FLI gfx light gray too.
2006-04-19 05:48
Oswald

Registered: Apr 2002
Posts: 4766
fli bug = vic reads #$ff from screen ram.
2006-04-19 11:25
MRT
Account closed

Registered: Sep 2005
Posts: 149
Maybe a little off topic, but I've encountered another curious thing with the same setup.

I see some sort of character display at rasterline $32. Now the first badline occurs on $33 and I can't seem to manipulate the $32 line. But, when I clear the first line of all the characters in the first screen bank (no matter if the first bank is displayed), the rasterline $32 disapears.
Now, to be clearer... The displayed chars on $32 ARE NOT the same as the characters of the first screen bank. I don't know what is displayed there, but it only displays one of the multicolors and the character color.

What's this?
2006-04-19 11:32
Graham
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Registered: Dec 2002
Posts: 990
Quote: fli bug = vic reads #$ff from screen ram.

And "next opcode" from color RAM.
2006-04-19 12:30
Monte Carlos

Registered: Jun 2004
Posts: 304
It sounds, that your starting your fli one line too late.
Check, if you really can do 200 lines fli and not only 198 or 199. You can see it, if theres no fli switches in the last 3 lines or so.
Did you open the borders for fliing ?

Monte
2006-04-19 14:21
MRT
Account closed

Registered: Sep 2005
Posts: 149
Nope, no open borders...
And yes, I'm doing 200 lines
:-S

And I'm starting fli on line $33, but even before $33 I update $d018 with the right value...
2006-04-19 14:27
WVL

Registered: Mar 2002
Posts: 868
Quote: Nope, no open borders...
And yes, I'm doing 200 lines
:-S

And I'm starting fli on line $33, but even before $33 I update $d018 with the right value...


You can't do 200 lines if you're starting at rasterline $33.. you have to open the borders and start at line $30 if you want to have 200 lines...

This is because badlines are limited to $30-$f7..
2006-04-19 14:39
MRT
Account closed

Registered: Sep 2005
Posts: 149
Sorry... must be stoned again... ;-)

Yes Monte Carlos & WVL...
You're both right. Thanx. I was starting one line too late. Curious though, because I was starting on line $33 when the bug appeared, but now I'm starting on $32 and the bug is gone. BUT, the amount of lines displayed seem to be the same as before... 8-S
2006-08-29 14:03
Viktor
Account closed

Registered: Apr 2002
Posts: 78
Have somebody ever tried the fli and the multi char mode together?

Will it cause something interesting? A new format or something another?
2006-08-29 14:23
Jetboy
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Registered: Jul 2006
Posts: 180
It's there since forever - "DisplayList" like effects are done like that.
2006-08-29 14:37
Oswald

Registered: Apr 2002
Posts: 4766
displaylist like effects are not using fli, instead they stretch the very same line forever and change d018 each line to display different gfx.

fli and multi chars together wont really give you anything that couldnt be done easyer using another trick. (see above)
2006-08-29 14:59
Viktor
Account closed

Registered: Apr 2002
Posts: 78
Thanks Oswald.

Viktor
2006-08-29 15:11
Jetboy
Account closed

Registered: Jul 2006
Posts: 180
Quote: displaylist like effects are not using fli, instead they stretch the very same line forever and change d018 each line to display different gfx.

fli and multi chars together wont really give you anything that couldnt be done easyer using another trick. (see above)


But that's almost exactly the same as FLI.

First charline in fli is stretched, while bitmap stays unstretched, and changed every line.

In Displaylist-like effects, first char line is stretched and changed every line.

It's not that big difference I would say. Only small difference in cycling.

BTW. how to get rid of the garbage after displaying fli, when you have border color other than black?
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