Newsgroups: comp.sys.amiga.programmer
Path: utzoo!utgpu!watserv1!watdragon!rose!ccplumb
From: ccplumb@rose.uwaterloo.ca (Colin Plumb)
Subject: Re: SuperBitMap Layers, etc.
Message-ID: <1991Mar6.193942.1842@watdragon.waterloo.edu>
Keywords: SuperBitMap, Layers, Graphics
Sender: daemon@watdragon.waterloo.edu (Owner of Many System Processes)
Organization: University of Waterloo
References: <27D2B7A7.3CE7@ibma0.cs.uiuc.edu>
Date: Wed, 6 Mar 1991 19:39:42 GMT
Lines: 43

menelli@sunc7.cs.uiuc.edu (Ron Menelli) wrote:
>I've got a bit of a dilemma that I hope someone can assist me with. Here is
>some background...
>
>I need to have four completely borderless, full screen windows on a custom
>screen. They are intended to act as "pseudo screens". Also, I need to write
>pixel by pixel onto this screen. I tried WritePixel(), which worked but
>was abysmally slow. I've spent much time attempting to replace it with
>something of my own that is faster...

Since you say later this is a SMART_REFRESH window, why not just go to 4
separate screens?  The 4 windows take up as much memory and are, as you've
observed, less efficient to work with.

>What I did was write a bit of code that writes directly to a BitMap structure
>in hopes that this was what I was looking for. It turned out to be a good
>four or five times faster than WritePixel(), but unfortunately, due to my
>lack of knowledge of the workings of low-level Amiga graphics, I was quite
>surprised to find out that writing to any of the four stacked windows resulted
>in the image being displayed on the frontmost window. This, of course, does
>me no good.

Of course; the primary BitMap structure points to the screen; the information
about what's obscured is hidden in the bowels of the layers.library and
you should go through the graphics.library to get at it.

>So, my question to everyone is, how can I solve this problem? Apparently
>CopySBitMap must attempt to 'refresh' (for lack of a better word) the
>ENTIRE screen, whereas I'm only dealing with a few pixels (usually 7 at a
>time). Can I tell it to update everything it needs to based on the small
>changes I make instead of the whole (mostly static) screen? Any suggestions
>are most appreciated.

Well, if the pixels are widely scattered, you're stuck with WritePixel().
If they're clumped, you can write them into a temporary buffer and use
one blit to write them, which might be faster than WritePixel(), although
just 7 pixels isn't much.

I don't see how to do what you're trying to do.  If you described your
application, maybe I could suggest something else you might try which
would be faster.
-- 
	-Colin