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  Little math problem with rotation :)  (Read 1048 times)
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Offline appel

JGO Wizard


Medals: 80
Projects: 4


I always win!


« Posted 2007-12-23 21:26:33 »

Ok, this might be a fundamental math problem, but I'm not getting it, maybe I need a little tip.  Grin


So, I have a unit (top-down-view), which is rotated at 0° when looking up (north), 90° when looking east, 180° south, 270° west and there is no 360°, it goes back to 0°.

Let's imagine the unit is looking east (90°), and I received a new rotation that the unit needs to smoothly transition to, let's say this is 340°.

Now I need to figure out if I need to rotate the unit clockwise or counter-clockwise. In this case I need to rotate counter-clockwise since it's the shortest distance to the new angle (I only need to rotate 110° instead of 250° if I would rotate clockwise!).

How would you do this?
Offline appel

JGO Wizard


Medals: 80
Projects: 4


I always win!


« Reply #1 - Posted 2007-12-23 22:01:56 »

Nm, MatthiasM worked it out for me Smiley

Here's the code I implemented.

rotation = the current rotation
directionAngle = the rotation I want to be at!

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   private void updateRotation(int delta) {
      float previous = rotation;

      // next two lines important! x is negative on CCW, but positive on CW!
      float x = (((directionAngle-rotation)%360)+360)%360;
      if(x > 180) x -= 360;
     
      if(x > 0) {
         rotation = (rotation+((float)delta*DEFAULT_ROTATION_SPEED));
         if(rotation > directionAngle && previous < directionAngle)
            rotation = directionAngle;
         rotation = rotation%360;
      } else {
         rotation = (rotation-((float)delta*DEFAULT_ROTATION_SPEED));
         if(rotation < directionAngle && previous > directionAngle)
            rotation = directionAngle;
         rotation = rotation%360;
      }
     
   }
Offline Mr_Light

Senior Devvie


Medals: 1


shiny.


« Reply #2 - Posted 2007-12-24 18:43:25 »

if(new > 360 || new < 1) throw illegalArgumentException("not a legal value for ... ");
return (new>old) ? (old-new)  > 180 : !((new-old)  > 180);

returns true if clockwise false otherwise.


I should write a unittest for it and check if it actually works, I'm too tired now. tbh considering how sleepy I am it might be bullshit altogether.


It's harder to read code than to write it. - it's even harder to write readable code.

The gospel of brother Riven: "The guarantee that all bugs are in *your* code is worth gold." Amen brother a-m-e-n.
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