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Re: scrolling

Subject: Re: scrolling
From: Luc Beurton <>
Date: Mon, 27 Nov 95 17:20:26 MET
In-reply-to: <>; from "Per Fogelstrom" at Nov 27, 95 3:32 pm
Mailer: Elm [revision: 70.85]
> Hmm, have you considered rendering the screen from a text copy of the
> screen instead of scrolling? I'm not familiar enough with the G364 but
> here are a couple of reasons it may be faster:
>       o The read access time to the v-ram can be long enough to
>         ruin the performance completely. Optimizing copy loops
>         in the driver is just waste of time.
>         o Writes to the board might be pipelined so it can sustain
>           a greater bandwith than reads.
>         o Cached reads clobber the cache even if it's increases the
>         read speed some.
>         o Uncached reads is a pain if you have to do a lot.....
>       o By rendering chars scanlinewise writes to the vram can be
>           minimized. And of course optimizing scanline length depending
>           on how long the lines are..
>         o And many more reasons..
> It might be easier to get rerendering working than some kind of hardware
> scrolling. Also hardware scroll looses if you want to implement scroll
> regions as in VT emulation.
> Also, you don't have to consider vram configurations so much.
> You could measure the character rendering speed by filling the screen
> with N characters without scrolling N times and time it.
> Just a thought....
> Per


I think there are two differents things:
 - Redrawing a new screen
 - Scrolling one or X lines.

I don't know well VT Emulation, but for Linux/68K there are two fonctions
(scrollup,scrolldown) which use the graphic for doing a graph scrolling.
not a text scolling. I thought that 'vi' or 'more' or ... use the scroll of
VT emulation which use some graph scrolling...

But it was only a test. I think text scrolling imply a lot of memory moving .


PS: I like playing with graphics board

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