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Amiga Collections: Various
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DevDisk 65 (1989)(DevWare PD).zip
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mypixel
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pixel.doc
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1990-07-11
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Pixel.Doc by Thomas J. Eshelman, Reading, Pa. 6/23/89
There are eight files in this archive: mypixel, mypixel.c, pixel.asm,
onepixel.s, onepixel, two .o files and the one you're reading. This series
begins a seminar on writing and interfacing routines on the Amiga that are
fast enough to comprise arcade games. I must assume the reader has a passing
knowlege of the C language as well as 68K assembler. Expertise is not
required, because the undersigned hardly holds himself thus. You will
"ln +cdb mypixel.o pixel.o -lc". (onepixel.s is a separate program here for
the programmer without benefit of Manx. The loop is absent in this program.)
This first program, mypixel, represents experiments with original Public
Domain code by Geodesic Publications. It is written merely to familiarize
the reader with the somewhat peculiar system used by the C language to pass
arguments on the stack. Further, careful study of the instructions that
set or reset the user-selected bit (coordinate) within the bitplane under
scrutiny, will very clearly illustrate exactly what is meant by the term,
"bit-plane graphics". The comments are copious, which makes for much
easier reading than having explanations one place and code in another.
We will simply fill a window with a rainbow....the hard way, pixel by
pixel; then restore it. (The easy way is to write a very short copper
list program.)
Why assembler? First, because when we get around to using the blitter,
speed means everything. Second, there are bugs in at least one of the
ultra-important system routines that noone has been able to kill in four
years! This means, you must write your own material.
This program makes the increased speed of the 2500 very obvious to the
fortunate owner. In addition readers should experiment by rearranging the
code in such fashion that it is inline within the C module just to
experience the speed increase afforded.
Since I am leading up to the blitter and sound routines of the small,
arcade game, LilGame, you may wish to get a copy if only to see the
direction we will be taking.
Regards. Tom Eshelman