[Coco] hardware scrolling

[Simon Jonassen]

Hey Steve...

I beg to differ....

The only thing i'm doing is shifting from 16 to 32 byte mode with 42 byte
dma mode enabled on a per line basis....
Then varying the raster split lines.... THERE IS NO SOFTWARE COPYING OF
SCREEN RAM AT ALL !!!

So if i'm not copying the bytes in software, then the hardware must be doing
it for me !

I would call that HARDWARE scrolling....

The vdg/sam counters are being confused to give various effects....

/Simon :-)
 

-----Oprindelig meddelelse-----
Fra: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] På
vegne af Steve Bjork
Sendt: 26. oktober 2013 19:31
Til: CoCoList for Color Computer Enthusiasts
Emne: Re: [Coco] hardware scrolling

I agree Nick, I've seen stuff like this while working on code that crashed.

Not very useful with all that screen trash and the fact you spend all of the
cpu time "scrolling" the screen.

Now, I did make the screen shake in my Canyon Climber and scrolling in
Desert Rider games for Tandy.  (Switching between 3K and 6K screen
sizes.)  Even though the screen did scroll down, I would hardly call any of
this stuff hardware scrolling by any means.

In the years before the CoCo 3, we did a lot of "tricks" on the VDG/SAM to
come up with new display modes.  Most of those tricks did not carry over to
the CoCo3, so they been lost to the ages. It's a little like indoor pluming.
The Roman Empire had it over 2,000 year ago and was lost of 100's of years
because of the dark ages.

As you know nick, the CoCo 3 can do true hardware scrolling. Marty's
Nightmare and other CoCo 3 games are good examples.

Steve


On 10/25/2013 10:53 PM, Nick Marentes wrote:
> This is not a new feature. It's been known. I just don't think that 
> anyone used it.
>
> Does anyone know of a CoCo 1/2 game that actually used the ability to 
> set start of video for vertical or horizontal scrolling? I think 
> everyone just used software which allowed for 1 byte movement. As it 
> stands, it jumps in increments of several bytes (6?).
>
> Also, same problem as the CoCo3 GIME... it moves the whole screen.
>
> Simon, your next challenge is split screen scrolling which I think the 
> VDG would be able to do by syncing on the horizontal scanlines and 
> changing the $FF22 at set points.


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