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000209_amos-request@svcs1.digex.net_Fri Apr 25 09:55:41 1997.msg
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From: Lee S Howarth <L.S.Howarth@cms.salford.ac.uk>
To: amos-list@access.digex.net
Message-ID: <80256484.003C4928.00@cms-notes-a.salford.ac.uk>
Date: Fri, 25 Apr 1997 12:23:16 +0100
Subject: re:amospro screens
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Mush...
your logic is a bit awry when you come to talking about your c2p stuff...
when you say about POKEing the colours to your reserved data store, that is
correct BUT then you say to COPY it to the screen, err, why not write to
the screen directly... IF and thats a big IF, the Amiga even had a chunky
screen :-)
Thats the whole point of a c2p routine, it converts the chunky byte per
pixel data to the Amigas planar screen display... The amigas display is
constructed of bitplanes, let me explain:
the amiga has diffrerent screen modes, OK
2 cols = 1 bitplane
4 cols = 2 bitplanes
8 cols = 3 bitplanes
16 cols = 4 bitplanes
32 cols = 5 bitplanes
64 cols = 6 bitplanes
128 cols = 7 bitplanes
256 cols = 8 bitplanes
now, a bitplane is basically a sheet which for a 320x256 will be 40 bytes X
256 lines. now 40 bytes X 8 = 320 and a byte contains the 8 bits which
represent a pixel on/off. Now with a 2 colour screen(eg. black and white)
you have 1 bitplane and if you want to set the 2nd pixel on the first line
you would set the first byte as %01000000
Now when you start adding more colours, more bitplanes are added(see table
above) and diffrerent combinations of set bits on the bitplanes will show
different colours on the screen.
bitplane 0, first line, first byte: 01000000
bitplane 1,first line first byte: 01000000 now this would show
colour 3 on the 2nd pixel of the top line. (the colours
range from 0-no of cols) remember
i hope that sort of clears things up a little, i`m not very g00d at
explaining things, i left out things like ham mode becoz they just makes
things even more difficult ;-)
My STRONG advice is to not even bother to write your own c2p (not yet
anyway ;-) and use one of the many freely available ones from the PD. I
use a few at the moment (depending on the situation, one of them uses a 2mb
fastmem buffer, hehe) and i use the Call command to call the compiled
assembler program from a bank. Doing a c2p in AMOS code would be slow and
useless, the c2p HAS to be quick for it to be useful and I doubt ANYBODY
could write a c2p routine in AMOS that could compete with an assembler one
:-)
Melee The Student who has just bought an 50mhz FPU for my 50mhz Amiga, and
18mb, and 850mb 3.5" hardrive, and ide-cd
drive... Anybody got any docs on how to code FPUs ???? (in assembler).