On (19 Jun 97) Christopher Butler wrote to Jerry Coffin...
 CB> Hi Jerry!
Hello,
 CB>> (guess what I'm trying to do now)
 JC> Animation perhaps?
 CB> Screen bouncing... (as you see in beat-em-ups when someone gets hurld
 CB> to the ground)...
Ah, for that you'd definitely want to change the start address rather
then moving things in memory...
 JC> If at all possible, I'd avoid ever reading from the screen.
 CB> Hmm... Why's that then? I've always thought its okay, and
 CB> occaisionally, practically essential. eg, a program I wrote
 CB> in QuickBasic drew a random starfield with a little text message
 CB> bouncing around. I could leave the text and starfield routines
 CB> seperate, and just check whether the pixel I was about to
 CB> plot a star to was black, and if not, don't plot the pixel...
Once in a while, under strange circumstances, it's reasonable.  However,
I'd keep in mind that reading from the screen is a LOT slower ( as a
rule) than reading from other memory.  If you can afford the memory,
you're usually better off writing the intermediate stuff to a buffer off
screen, then writing only the final result to the screen itself.
    Later,
    Jerry.
... The Universe is a figment of its own imagination.
--- PPoint 1.90
---------------