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From: toddpw@cco.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: Screen Values??
Message-ID: <1991Dec9.183220.937@cco.caltech.edu>
Date: 9 Dec 91 18:32:20 GMT
References: <1991Dec08.141621.14323@crash.cts.com>
Organization: California Institute of Technology, Pasadena
Lines: 56
qd@pro-calgary.cts.com (Quinn Dunki) writes:
>I'm working on my Knights of Legend GS right now, but I've hit a big-time
>glitch. Maybe somebody can help? I've written this function that just
>returns (ORCA/C, by the way) the color number of a given pixel. However, no
>matter what's on the screen, no matter what values I give it, it always
Probably a bug in the compiler. Try the following, which is considerably
faster and does precisely what your code does, although in not precisely
the same order, and considerably better optimized than anything Orca/C can
produce:
int gethex (int x, int y)
{
asm {
lda y
asl a
asl a
asl a
asl a
asl a
sta y
asl a
asl a
adc y /* computes y*160 as y*(2^5)*(1+2^2) */
lsr x
bcs odd
adc x
tax
lda >0xe12000,x
and #0xf0
lsr a
lsr a
lsr a
lsr a
bra out
odd:
clc
adc x
tax
lda >0xe12000,x
and #0x0f
out:
sta x
}
return x;
}
This assumes of course that you do not intend to support arbitrary screen
sizes (no biggie for a game) and that you will be calling this often enough
to make the assembly worthwhile -- which I suspect is the case, especially
with Orca/C (hint, BTW, always use x&1 instead of x%2 -- Orca/C doesn't
optimize the modulo computation).
Todd Whitesel
toddpw @ tybalt.caltech.edu
Path: ns-mx!uunet!vuse.vanderbilt.edu!benson
From: benson@vuse.vanderbilt.edu (Paul BaJa Benson)
Newsgroups: comp.sys.apple2
Subject: Re: Screen Values??
Message-ID: <1991Dec9.213742.1846@vuse.vanderbilt.edu>
Date: 9 Dec 91 21:37:42 GMT
References: <1991Dec08.141621.14323@crash.cts.com>
Sender: news@vuse.vanderbilt.edu
Organization: Vanderbilt Univ., Engineering (SERG), Nashvegas, TN
Lines: 49
Nntp-Posting-Host: cad1
In article <1991Dec08.141621.14323@crash.cts.com> qd@pro-calgary.cts.com (Quinn Dunki) writes:
~returns 11. Even if there isn't anything on the screen that is color #11 in
~ANY pallette. Here she is:
~
~int gethex(int x, int y)
~
~{
~char c;
~
~ c=*(screen+x/2+y*160);
~ if ((x%2)==0) {
~ c=c&0xF0;
~ c>>=4;
~ }
~ else c=c&0x0F;
~ return c;
~}
~
~Can anybody see any reason this shouldn't work?
Using Todd's excellent assembly code is probably your best choice in this
case, as this routine will probably be called a lot and his code is to the
point. But, let's make sure you did not over look some C problems that
might crop up in different functions.
1 - How is 'screen' defined. Hopefully it is a _char_ pointer and is
pointing to the proper location. So something like this should be in
your code somewhere:
char *screen;
screen = (char *) 0xe12000;
This can all be put on one line, this just explains it better.
2 - Did you pre-declare the function gethex? If you are calling it from a
function 'above' gethex and you did not pre-declare it, it is expecting
an int function with no passed parameters. This would mess up your
stack, and thus your answer, and invariably your program.
3 - You have defined c to be char and you have declared an int function.
Your return statement is returning a char, either convert c to int or
make the function a char function (better).
Hope this helps.
s
--
Paul 'BaJa' Benson
Vanderbilt University - Space Electronics Research Group
GEnie: P.Benson1 Net: benson@vuse.vanderbilt.edu