NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/sys/atari/st/tech/6304

Internet Message Format | 1992-12-16 | 3.0 KB

Path: sparky!uunet!mcsun!uknet!gdt!aber!hrs
From: [e-mail] (Herbert Martin Sauro)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Sending objc_draw to a memory buffer rather than screen
Message-ID: <[e-mail]>
Date: 11 Dec 92 09:47:43 GMT
References: <[e-mail]>
Organization: University of Wales, Aberystwyth
Lines: 54

In article <[e-mail]> [e-mail] writes:
>
>In article <[e-mail]>, [e-mail] (Herbert Martin Sauro) writes:
>>I'm trying to write a scrollable list box. I've gone through a number of
>>attempts. The best one so far was blitting n-1 of the entries in the list
>>and writing the nth item using objc_draw as the list is scrolled.
>>The trouble with this was if
>>the user scrolled more than one item at a time this method no longer worked
>>and instead the whole list box had to be redrawn (i.e using objc_draw)
>>at the new position - which makes for flickering and it's slow.
>>If the list box only moves one item at a time
>>the n-1 blit method works a treat and without any flicker -- the list
>>can also scroll pretty fast.
>
>    Can't you vsync ? And what's wrong with a window ?

The trouble with using a window is that one doesn't recveive instant feedback
from the slider as its draged etc. so that the window contents aren't
updated until after the slider has finished moving.

>
>>I'm now thinking of another method, this time to hold the entire list
>>(or at least the section that is being displayed) in a memory buffer
>>and as the list is scrolled just blit the appropriate section out to
>>the screen. The trouble I'm having is how do I get such a list into
>>a memory buffer in the first place. It's a shame that one can't redirect
>>the output from the objc_draw command to a memory buffer rather than
>>the screen (or can one?). So the question is, how can one store dialogs,
>>sections of object trees etc in memory (as bit maps I mean) so that they
>>can be blitted out to the screen at will?
>
>    Yes you can redirect objc_draw() output by changing the screen physical
>address. Of course it won't speed anything up, in fact it'll be slower plus
>you'll soak up RAM. Xcontrl list boxes scroll o.k with a decent accelerator.
>
>    Adam.

In Xcontrol one has to implement one own list boxes, the only related
calls that Xcontrol suppliy (as far as I can tell) are slider controls,
you have to build your own list box.

One could redirect objc_draw on to an alternative logical screen (I'd
forgotten that one), but it takes up large amounts of RAM (as you mention).

Actually I have a question about logical screens, I know that all
drwing is done on the logical screen but where do vro_cpyfm blits
come from, the logical or physical screen?

Herb
--
/******************************************************************************
Herbert Sauro                                   e-mail: [e-mail]
Biological Sciences                              phone: [phone]
Univesity College of Wales