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Forums > C64 Coding > 1 char wide gray area when repeating chars
2018-09-07 16:41
Golara

Registered: Jan 2018
Posts: 81
1 char wide gray area when repeating chars

I was trying to avoid badlines in my raster code but accidentally got the repeating chars, which I thought was cool because now I could also display some single color bitmap... and it works, but there's a 1 char wide gray area, like FLI bug ? Is it normal ? Can it be avoided ? Can't cover it up with sprites.
2018-09-07 19:33
ChristopherJam

Registered: Aug 2004
Posts: 836
Perhaps try moving the d011 write that triggers the DMA at the top of the screen to one cycle earlier?

(assuming of course you're doing any DMA per frame at all, rather than inheriting character data from the last frame before you start the effect)

Alternately, use a multicolour bitmap and just set the pixels in the first column to zero, or use character mode and clear the character definition for character #255.
2018-09-07 19:59
Groepaz

Registered: Dec 2001
Posts: 8713
hard to tell without seeing the code... but indeed, moving the d011 write is probably the way to go. if that alone doesnt help, try making the per-line timing one cycle shorter
2018-09-07 20:04
Golara

Registered: Jan 2018
Posts: 81
Quote: Perhaps try moving the d011 write that triggers the DMA at the top of the screen to one cycle earlier?

(assuming of course you're doing any DMA per frame at all, rather than inheriting character data from the last frame before you start the effect)

Alternately, use a multicolour bitmap and just set the pixels in the first column to zero, or use character mode and clear the character definition for character #255.


I'm doing it in the middle of the screen, I'm repeating 10th line of chars. 9 above display a logo.

I removed one nop before the raster loop and now it is flashing like I have unstable raster.... and turns out it is... moved the irq but didn't change the line number to compare when loosing the last jitter cycle. Thanks for the suggestion.

This mode is really cool, it would be amazing if it was an intended feature, like flip this bit to get one badline per screen and you can have bitmap with the same colors.

EDIT. If you're thinking "why did you post before doing the obvious, changing the timing a little bit". I did, but inside the raster loop, moving the d011 write about, thought my raster is stable and the loop always starts at the beggining of the line. Feel stupid man
2018-09-07 20:09
Groepaz

Registered: Dec 2001
Posts: 8713
remember that if you somehow trigger a DMA ("FLI") then the timing _is_ stable all of a sudden :)
2018-09-07 20:13
Golara

Registered: Jan 2018
Posts: 81
Quote: remember that if you somehow trigger a DMA ("FLI") then the timing _is_ stable all of a sudden :)

Yeah, I've read about it (and it makes sence since vic takes away the control and you gain it back exactly in the right border) but didn't use it yet. Maybe for the next part.
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