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From: uzun@pnet01.cts.com (Roger Uzun)
Newsgroups: rec.games.programmer,comp.sys.amiga.tech
Subject: Re: Animation Speed & Redraw
Message-ID: <4275@crash.cts.com>
Date: 6 Sep 90 22:36:01 GMT
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>>Dallas Hodgson wrote:  No need for a 3rd bitmap what I was referring to was
>>display screen A while clearing out B, then drawing objects into B, 
>>if you have a large background then you can replace clearing out
>>B with copying background into B.

That is what a 3rd bitmap is used for!  to be a "clean" copy of the
background.  Most modern games have very detailed backgrounds, and
the method you proposed does call for a 3rd bitmap to be maintained,
the 3rd bitmap is of a clean background, and is never displayed.

Most all developers on the amiga, who develop for the amiga, make
use of hardware sprites, they are hardly a headache at all, while
not a complete solution, for most games they take much of the
load off the processor blitter, 64 pixel width of 16 color object
per scanline is not trivial, neither is 128 pixel width of 4 color
object (well really 3 and 15 colors but..) The one scanline gap
between objects is not a big problem in most cases since sprites can
be ANY height.

Blood Money uses mostly all sprites.

Heart of the Dragon makes extensive use of sprites hardware.

With the older agnus, I think you cannot blit a 320X200X4 bit screen
is a single pass, but I forget for sure.  

I have never tried the blast out the background technique (using the
3rd off screen bitmap) on the amiga, but I have on the Apple //, Apple
Macintosh II (8 bit video), and Atari computers.  It was a total
disaster on the Mac II, the processor could easily animate many 
rectangular objects with shadow masks for cookie-cutter like
effects, and copying in the background each time just killed
performance, you got like 8 frames/sec using the 3rd bitmap approach.
Of course this was a 640X480X8 bit screen.  Still in my experience with
the Amiga, I do not feel that blitting in the entire background would
be as fast, or even nearly so, as using sprites and/or raster objects
with shadow masks.

Maybe I will do a benchmark and see how it is, for now all I can say
is my feeling is that the 3 bitmap approach will be slower.

-Roger

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