Laurens Holst wrote:
> I have -almost- finished my scrollroutine...
>
> It scrolls in all directions and it has got a screensplit at the bottom.
> It uses sprites to mask the borders and takes about 50% of your VDP-time,
> but with some modifications it will probably also be possible not to use
> sprites.
>
> It is based on 8x8 patterns, and it scrolls all 16 pixels (8 seemed to be
> too slow). This means that your screen will be 16 pixels smaller (240x212),
> but that's not a real disadvantage.
>
> However, one problemo...
> When I set the adjust while a VDP-command is executing, there appear some
> 'noise'-pixels on the screen. I can avoid that to happen by exact timing of
> my COPY's (execute them right after the V_BLANK-interrupt), but I would like
> that different (because it will also decrease the time left for other
> copies, i.e. the displaying of the character).
>
> Does anyone know a solution for that???
>
I had the same problem with these noise-pixels about 8 years ago in a horizontal
scrol in screen 5. Just a test back then if it was possible. I used a HMMM command
to copy the screen every 8 pixels. Per pixel scrolling happened with register 18. This
HMMM command used about 1.5 or 2 frames time (50 Hz) to complete. So it uses
about 25 % of the available time. The vertical lines where placed with 'vpokes'.
My scrol had only 5 directions (up, up-right, right, down-right, down) and a screen
split
in the top of the screen (16 pixels in height). The top-side of the screen had a
constant
value for register 18 the scrolling part ofcourse didn't.
The solution was changing the sequence in which the vdp registers where written:
are you writing register 18 before or after the command that you are executing.
>
> For example, during the screensplit I disable the screen, and at the end I
> enable it again. This however gave a white line at the lowest (second) line
> of the screensplit. I was able to solve this problem by making sure the
> screen was enabled during the H_BLANK-period...
>
> Is there some solution like this for the VDP_18-problem too???
>
> Thanks in advance,
> ~Grauw
>
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