What are masks?

Ok, sorry I'm asking so many questions, but I searched on masks (the most obvious thing I think) and didn't find anything. So please explain, what are masks (I know they are white pictures of the ship or waepon you are making), and what do they do?
I know this may sound dumb, but I'm just a newbie trying to make his own plugs

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You can run but then you die tired

It came as a surprise to me too, but they actually "mask" the ship from other objects. Sort of like the mask "cuts" the ships out of its square PICT-shape. Its really quite handy, except of course if you only make Borg-ships that don't rotate, then you won't need it.

(I'm sorry)
Denb

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But, oh, what a wicked world it was that drove a man to sin.

(This message has been edited by Denb (edited 08-26-2003).)

Masks are what allow ships and other objects to be have transparency, so that the black pixels making up their bitmaps aren't drawn on the screen. The mask has black where the ship doesn't exist and white where the ship does exist, and it looks like a cookie cutout of the ship. When the ships are drawn, first the mask is bitwise-OR'ed with the screen, so the black in the mask does nothing and the white in the mask turns that area to white. Then, the ship's image is bitwise-AND'ed with the screen, so the black again does nothing and the non-black is copied exactly.

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C:dos
C:dosrun
rundosrun