Re: Qbasic graphics.

 BBS: Inland Empire Archive
Date: 03-05-92 (11:56)             Number: 178
From: LAWRENCE MCALPIN             Refer#: NONE
  To: KAMEL DIDAN                   Recvd: NO  
Subj: Re: Qbasic graphics.           Conf: (11) Modula-2

In my MEGASprite! package I include some information on
ways to use those sprites in animation.  I'll try to
explain them to you so you can do that to with whatever you
use.  Basically, I define a sprite is a block-graphics area,
and you can 'GET' a sprite with the graphics GET command in
QBasic or QuickBASIC.

Once you have this sprite, there are two techniques I commonly use:

1) PUT the sprite wherever you want with the XOR parameter, then XOR it at
the same location to erase it, restoring the background.
Then XOR it again at the new location, and XOR it again
when you decide to move it.  Etc., etc.  It's easy to do,
but the problem is you'll get color bleed-through as the
background will blend in with the foreground (sprite).

2) Analyze your sprite using POINT for every non-background color (non-zero)
PSET a white pixel somewhere else on screen.  This should
come up with another sprite shaped the same but with white
for every colored pixel in your normal sprite.  GET both of
these sprites.  The 'normal' sprite is the one users of
your program will see, and the white sprite is a 'matte'.

To put the sprite onscreen without overwriting the
background but without causing color bleed-through, OR the
matte onto the background somewhere.  Then
AND the 'normal' sprite onto that.

To erase the sprite, you will have to have GET (got?) the
background area first though, and then just PUT the
background at that location, GET the new background you
will be overwriting, and do the OR/AND technique again.

This is a tad bit slower, uses more memory (as you have to
have three sprites in memory for each figure you want to
animate), but looks better.

I'm sure there are other techniques, but these are the only ones I've
basically used.   The latter technique I haven't used as
often, but it's worked fine in tests I made of EGA sprites
I created with my program on various backgrounds.

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