wrap angle?

BlitzMax Forums/BlitzMax Beginners Area/wrap angle?

Qweeg

(Posted 2005) [#1]

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

LarsG

(Posted 2005) [#2]

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..

Qweeg

(Posted 2005) [#3]

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.

Ibmurai

(Posted 2005) [#4]

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.

FlameDuck

(Posted 2005) [#5]

and yet in mathematics -10 mod 360 is 350 :D

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.

Sarge

(Posted 2005) [#6]

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 )

Zethrax

(Posted 2005) [#7]

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

Qweeg

(Posted 2005) [#8]

cool - thanks for all your tips guys.

Ibmurai

(Posted 2005) [#9]

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 :)

Hotcakes

(Posted 2005) [#10]

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

Sashnil

(Posted 2005) [#11]

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.