Path: utzoo!attcan!uunet!husc6!bloom-beacon!mit-eddie!uw-beaver!apollo!tweed
From: tweed@apollo.COM (David Tweed)
Newsgroups: comp.sys.apollo
Subject: Re:  ...animation
Summary: undraw, rather than erase
Message-ID: <4064ed4f.313a@apollo.COM>
Date: 21 Dec 88 21:09:00 GMT
References: <8812201611.AA09712@richter.mit.edu>
Reply-To: tweed@apollo.UUCP (David Tweed)
Organization: Apollo Computer, Chelmsford, MA
Lines: 35

In article <8812201611.AA09712@richter.mit.edu> krowitz@RICHTER.MIT.EDU (David Krowitz) writes:
>           .... Try to avoid BLT'ing whole screens -- the more
> data you have to move, the worse the flickering -- it's 
> frequently faster to erase only the section of the screen
> where something has changed and to redraw that small section.
> Take a look at the code for BZONE and STWAR in the ADUS library.
> They may give you a few ideas, although they both do line
> drawings, not filled-area graphics.
> 
>  -- David Krowitz

I've done some hacking to BZONE, and written a similar application
myself (asteroids). These programs actually "undraw" a figure in
order to move it. That is, the figure is drawn in black in its old
position, moved, then drawn in its visible color.

The objects are stored in GPR multi- or poly-line format so that
they can be passed directly to GPR for both drawing and undrawing.
This allows you to take advantage of whatever optimizations have
been implemented in GPR. In particular, I believe that on the
DN580(-T)/590, the entire operation is handled by the graphics
hardware.

(The only things BLT'd in BZONE are the little knob on
the end of the joystick, the little tank images that tell you how
many you have left, and the toggle switch. And they don't even bother
to use hidden memory to hold them!)

                                         -- Dave Tweed

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