wrap angle?

Just a quickie.

Can't see this anywhere, but I wondered if there was an equivalent to the DB Pro (sorry for swearing)- WRAPVALUE function? This takes an angle and returns it as the 0-360 equivalent; so 370 would return 10; -10 would return 350 etc. Should be relatively easy to write a function to do this if not - I just didn't want to re-invent the wheel if it already exists.

Cheers

mod the angle with 360?
ie.
wrap = angle mod 360

note: this doesn't work with negative values, so you'll have to check that first..

Thanks Lars - don't think that quite works for negative angles. For those you would need to subtract the result from 360 (I think).

so something:

wrap = angle mod 360
if wrap < 0 then wrap = 360 - wrap

I'll just use a function for this I guess - just wondered if it was already there, hidden away somewhere.

Yeah it doesn't work with negative values. And that's so weird - I've never seen a programming language mod function which did, and yet in mathematics -10 mod 360 is 350 :D

Maybe someone could explain why mod is never ever properly implemented like that - It would be more practical, imo.

No it isn't. The remainder of an integer division of 10 by 360, is never 350, regardless of whether one of the elements is negative.

If you want to be absolutely 100% sure, use trigonometry.

Something like this ?

Graphics 800,600,0
Local Angle:Int

Repeat
	Cls

		DrawRect Angle+GraphicsWidth()/2-20, GraphicsHeight()/2-20, 20, 20

		If KeyDown( Key_Right )
			Angle = ( Angle + 1 ) Mod 160
		End If

		If KeyDown( Key_Left )
			Angle = ( Angle - 1 ) Mod -160
		End If

		DrawText  Angle, 5, 5

	Flip
Until KeyHit( Key_Escape )

Here's my little wrapvalue function. Seems to work well enough with negative numbers.

Function F_WrapValue#( v# )
v# = v# / 360.0
Return ( v# - Floor# ( v# ) ) * 360.0
End Function

cool - thanks for all your tips guys.

FlameDuck: I guess it depends on how you interpret the modulo function. I believe it should return the index of the residue class in which the remainder belongs. Wikipedia says we're both right :)

Ugly, but works under all circumstances (off the top of my head, could be minor typos:), not limited to angles, which is a weird thing to do if you ask me:

Function QWrap#(value#,mix#,max#) ; A name from AmiBlitz days, I guess the BlitzPC equivalent should be FWrap
  If max-min=0
    Return min
  Else
    While (value>max) And (value<min)
      If value<min Then value=value+(max-min)
      If value>max Then value=value-(max-min)
    Wend
  EndIf
  Return value
End Function

not exactly what you're looking for but an alternative non the less.
You could have your 360 deg angles from 0 to 255 and do a bit operator to wrap it around.

your condition would look like this:

angle = (angle + 1) & 255

no if's or divisions.. once you hit 256, it auto wraps to 0. very fast.