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From: menelli@sunc7.cs.uiuc.edu (Ron Menelli)
Newsgroups: comp.sys.amiga.programmer
Subject: SuperBitMap Layers, etc.
Summary: Need a faster way to update
Keywords: SuperBitMap, Layers, Graphics
Message-ID: <27D2B7A7.3CE7@ibma0.cs.uiuc.edu>
Date: 4 Mar 91 21:09:59 GMT
Sender: news@ibma0.cs.uiuc.edu
Organization: University of Illinois at Urbana-Champaign
Lines: 36

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...

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.

My next attempt was trying to write to a SUPER_BITMAP (instead of 
SMART_REFRESH) window, so I could write to the superbitmap instead of the
common screen bitmap like I was doing before. This resulted in nothing being
displayed at all. After paging through the AutoDocs, I found the
CopySBitMap() function that updates layer information after a write to the
superbitmap structure. This made everything work, but it was MUCH slower than
WritePixel.

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.

Thanks,
Ron Menelli
menelli@cs.uiuc.edu
menelli@sumter.cso.uiuc.edu