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From: dale@amiga.UUCP (Dale Luck)
Newsgroups: comp.sys.amiga
Subject: Re: BltMaskBitMapRastPort
Message-ID: <1704@amiga.amiga.UUCP>
Date: Fri, 21-Aug-87 13:23:29 EDT
Article-I.D.: amiga.1704
Posted: Fri Aug 21 13:23:29 1987
Date-Received: Sun, 23-Aug-87 04:28:28 EDT
Reply-To: dale@amiga.UUCP (Dale Luck)
Organization: Commodore-Amiga Inc., 16795 Lark Ave. Suite 106, Los Gatos CA 95030
Lines: 33

In some article Keith writes:
>In article <493@rocky.STANFORD.EDU> rokicki@rocky.UUCP (Tomas Rokicki) writes:
>>Please note that an arbitrary rectangle *copy* requires all three
>>sources and the destination---A to mask out the edges of the
>>rectangle, B to fetch the source, C to fetch the destination, and
>>D to write the destination.  You could change minterms or a few
>>other things, but not too much more.
>
>Are you saying that it is not possible to do an arbitrary rectangle
>*copy* with a *mask plane* in a single operation because of this?  
>If so, that's a 2 and 2 I hadn't put together yet.  Couldn't A be
>a mask plane and serve to both mask out the edges of the rectangle, 
>as well as acting as a 'shape' mask for the object being copyied?
>
>Inquiring minds want to know.
>
>Keith Doyle
>
Yes, it is true that you can use one of the srcs as the mask plane and
the rectangle. And this works ok as long as you have simple bitmaps.
When you are blitting from a window to another window that has been
diced up because of overlappingness <sic?> , you need to dice that
mask up also into pieces. It is handy to have yet another simple mask
src that only places a rectangular mask to mask the mask. Also if
you are doing stuff more complicated then simple copy this to there
except for the bits I've zeroed in this mask, then you cannot use
the mask to cut out the rectangular areas. For example, if I want
complement those areas where there exists a 1, but I want to zero out
the bits where there is a 0 in the mask.
So to sum up, I really want another blitter term, just a rectangular
mask. Especially helps in the 'scrolling' cases where you have
overlapping source and destination.
Dale Luck