Path: chuka.playstation.co.uk!news
From: "Darren Jackson" <darren@tang.globalnet.co.uk>
Newsgroups: scee.yaroze.beginners
Subject: Re: angles, angles
Date: Sun, 22 Nov 1998 19:57:17 -0000
Organization: PlayStation Net Yaroze (SCEE)
Lines: 79
Message-ID: <739qi2$ekm13@chuka.playstation.co.uk>
References: <72spa7$dvm12@chuka.playstation.co.uk> <72sr28$dvm13@chuka.playstation.co.uk> <3652971c.228584498@news.playstation.co.uk> <731up3$olq9@chuka.playstation.co.uk> <3654E715.74C8@manc.u-net.com>
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James Shaughnessy wrote in message <3654E715.74C8@manc.u-net.com>...
>Darren Jackson wrote:
>> ONE=4096=1degree, right?
>> should I convert to degrees before using it in sin and cos?
>
>It depends on what your sin/cos library uses.  If you use my SINCOS.H
>lookup tables (see SCBUILD from my page plug plug ;-) ) then
>you can divide a full circle into whatever you want, including
>degrees if you wish:  "scbuild 360" gives proper 'degree' tables,
>so to do sin(90 degrees) just do: SIN[90] in your program.
>If you use "scbuild 1024" then sin(90 degrees) is SIN[256].
>(I assume you are aware that "SIN[]" is just an array, and not
>a slow maths function like "sin()")
>
>The result of SIN[] is multiplied by 4096 as the fixed point scaling
>function (nothing to do with the angle argument which I think you
>are confusing it with), so when you want to refer to it in it's "true"
>form, you must bitshift it right 12 times: (SIN[angle]>>12)
>
>There's no reason why you should use degrees though, it's best
>and more accurate to use say 1024.  For more accuracy (but more
>memory) use 4096 for a full circle. (SIN[4096] and COS[4096] tables
>would add 32Kb to the executable so not too bad anyhoo)
>
>Then use a pencil to ram up your nose to mash up the part of the brain
>that always wants to think in degrees.  The only reason a circle was
>divided into 360 was because it was "quite near" to how many days that
>are in a year you know.  End of history lesson. 8-)
>4096 is dead easy to get used to though (1024 right-angle), just be
>glad we don't have to use RADIANS! (or that mutant Gradian..)



After a bit of thinking and a lot of trial and error, I came up with this,
which kinda does what I want but the sprite moves way to fast. Also, I am
not really sure what is going on, and I am not sure as to the accuracy (i.e.
how may different paths are they between 0 and 90degrees? and how do I get
more?) I am using the trig library generated by scbuild 4096. Am I on the
right track?

basically I want the sprite (tank) to move forward in the direction its
pointing, but I want it to go quite slowly.

code snippet :

if (PAD & PADup }
   {
   tank1.x_speed=(SIN[tank1.sprite.rotate/360]>>9);
   tank1.y_speed=-(COS[tank1.sprite.rotate/360]>>9);
   MovePlayer();
   }

  if (PAD & PADdown )
   {
   }


  if (PAD & PADright )
   {
   tank1.sprite.rotate+=ONE;
   }


  if (PAD & PADleft )
   {
   tank1.sprite.rotate-=ONE;
   }

void MovePlayer()
 {
 tank1.sprite.x += tank1.x_speed;
 tank1.sprite.y += tank1.y_speed;
 }


Darren