Mathematics - Rotation problem - GameCreators Forum

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Dragon Knight

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Location: Newcastle

Posted: 20th Mar 2010 19:19 Edited at: 20th Mar 2010 19:21

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I've had a late night drinking.. and a major headache, my problem solving has went out the window today.. and I'm requesting the help of my fellow TGC community

, Thanks in advance

The problem I have a ship that rotates towards an angle.

for example
DestAngle = 45
SourceAngle = 0

SourceAngle will +1 until it reaches 45

The problem occurs when the Source angle is at say 4 degrees, and the destAngle is at 356 degrees, currently my if statements are very simple just adding and decreasing depending on if it's lower / higher.

Any thought on how to fix this, i'm guessing having another claus saying if SourceAngle<180 and DesAngle>180 then decrease until less than 0 and bang flip it to 360, and the same vise versa.

What do you guys think?

http://www.hybridwolves.co.uk

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C0wbox

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Posted: 20th Mar 2010 19:29

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I'm sure you could try something with wrapvalue.

As for the original part, don't use if statements, use:

+ Code Snippet

DEST=DEST+((CURR-DEST)/(((CURR-DEST)*(CURR-DEST))^0.5))

As this calls no functions and is just pure mathematics.
(Where DEST is the destination value and CURR is the current value)
(A more logical form uses abs() at the end:

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DEST=DEST+((CURR-DEST)/abs(CURR-DEST))

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Link102

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Location: On your head, weeeeee!

Posted: 20th Mar 2010 19:33 Edited at: 20th Mar 2010 19:35

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356 degrees = -4 degrees

wait. think about it...
...
...
...
ok, go.

edit:
I can't resist.

speudo code:

if wrapvalue(destangle) = < 360 and > 180 then destangle = destangle - 360

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Dragon Knight

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Location: Newcastle

Posted: 20th Mar 2010 19:48 Edited at: 20th Mar 2010 19:49

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Link that approach doesn't work, just tried it.

C0wbox, I've tried both and messed around with them for a while and didn't get the results I wanted

.

e.g.
Source = 5
Destination = 355

It will still increment the source upwards, instead of taking it away until less than 0 switching it to 360

so instead of incrementing 350 times upwards i'd like to:
Decrease the 5 by 10 decrements and get 360 in 10 moves... instead of the 350 increments i'd have to do, going upwards.

http://www.hybridwolves.co.uk

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Dragon Knight

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Posted: 20th Mar 2010 20:06

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Got it solved... but in a very bad hacker way...

I had the rotation being got from a atan2 from an on screen joystick.
Angles Vary between -3.14 and 3.14 ish.. it's done in radians
Anyway got the code to work by doing the following

+ Code Snippet

if ThumbStick<0
  if DesAng > 0 && SourceAng<0
       inc SourceAng,0.2
       if SourceAng>3.14
          SourceAng=-3.14
       endif
  endif
  if DesAng < 0 && SourceAng>0
       dec SourceAng,0.2
       if SourceAng<-3.14
          SourceAng=3.14
       endif
  endif
endif

if SourceAng>DestAngle
   inc SourceAng,0.1
endif
if SourceAng<DestAngle
   dec SourceAng,0.1
endif

http://www.hybridwolves.co.uk

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Robert The Robot

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Location: Fireball XL5

Posted: 20th Mar 2010 20:07

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Source= 5, Destination = 355
DirectionOne: Destination - Source = 355 - 5 = 350.
DirectionTwo = Wrapvalue(Source - Destination) = Wrap(5 - 355) = Wrap(-350) = 10
DirectionTwo<Directionone so move negative 10 degrees.

To confirm it works:
Source= 0, Destination = 45
DirectionOne: Destination - Source = 45 - 0 = 45.
DirectionTwo = Wrapvalue(0 - 45) = Wrap(-45) = 315.
Directionone<DirectionTwo so move +45 degrees
Hope this hhelps!

"I wish I was a spaceman, the fastest guy alive. I'd fly you round the universe, in Fireball XL5..."

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Jimpo

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Posted: 20th Mar 2010 20:15

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Here's a solution that is a little cleaner:

+ Code Snippet

DestAngle = 200
SourceAngle = 170

repeat
   SourceAngle=NewAngle(SourceAngle,DestAngle)
   print SourceAngle
until SourceAngle=DestAngle

wait key
print "-"

DestAngle = 355
SourceAngle = 5

repeat
   SourceAngle=NewAngle(SourceAngle,DestAngle)
   print SourceAngle
until SourceAngle=DestAngle

wait key

end

function NewAngle(source,dest)
   `determine whether to invert direction
   if abs(dest-source)>180
      direction=-1
   else
      direction=1
   endif
   if source<dest
      inc source,direction
   endif
   if source>dest
      dec source,direction
   endif
   source=wrapvalue(source)
endfunction source

The function is what you want, the rest is just to test.

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Dragon Knight

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Posted: 20th Mar 2010 20:38 Edited at: 20th Mar 2010 20:40

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Jimpo, perfect

Substituting it in now

C0wbox, I guess that's what you were hinting at but the use of changing DEST in your formulas confused me a bit, as to what you were doing.

Everyone, thanks for your help

it's much appreciated.

http://www.hybridwolves.co.uk

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C0wbox

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Posted: 21st Mar 2010 02:18

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My formula was just to move the current value to the destination value. - It wasn't going to solve your problem.

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