Date: Tue, 11 Oct 1994 08:57:03 -0400 (EDT)
From: Edwin Phillips <flaregun AT strauss DOT udel DOT edu>
To: Kimberley Burchett <OKRA AT max DOT tiac DOT net>
Cc: DJGPP Mailing List <djgpp AT sun DOT soe DOT clarkson DOT edu>
Subject: Re: keyboard messups!!!! :(

On Mon, 10 Oct 1994, Kimberley Burchett wrote:

> 
> On Sun, 9 Oct 1994, Curtiss Cicco wrote:
> 
> > >  do {
> > >    FixRotate(x,y,angle,&x,&y);
> > >    PutPixel(FixWhole(x)+160, FixWhole(y)+120, 15);
> > >    while(kbhit() == 0);
> > >  } while(getch() != 'q');
> > >  CloseVGA();
> > >}
> 

	I assume that FixRotate() computes:

 x = x*cos(angle) - y*sin(angle), and y = x*sin(angle) + y*cos(angle)

with fixed point math, 16.16 bit.  If angle is constant across calls, you 
should see x and y trace a circle (right?) about the origin, at an interval 
of the angle.  But, you say that kbhit() and getch() are cause the values 
of x, and y, to NOT behave in this way.  I suggestion I can offer is to 
open a file and right out x,y at each step through the loop.  Then take 
out to kbhit() etc. and write them again.  If the values don't match, 
then there may be a problem with having kbhit() or getch().  You could 
alternative step through the program in gdb, or (I don't know if gdb will 
do this) set a breakpoint to occur if x or y changes.  Make sure that 
FixRotate() is the only function changing them.  Maybe PutPixel is 
modifying x or y accidently (it's making a pointer into screen mem 
right?).  Make sure that the values are correct, and find out what is 
changing them to be incorrect.  This should be easy since it's a small 
prog (at least the part you showed us).

	Hope this helps,
	Ed

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/* Ed Phillips  flaregun AT strauss DOT udel DOT edu      University of Delaware       */
/* Jr Systems Programmer  (302) 831-6082    IT/Network and Systems Services */
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