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 Little math problem with rotation :)  (Read 839 times) 0 Members and 1 Guest are viewing this topic.
appel

JGO Wizard

Medals: 69
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.

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?

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appel

JGO Wizard

Medals: 69
Projects: 4

I always win!

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

Nm, MatthiasM worked it out for me

Here's the code I implemented.

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

 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20 `   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;      }         }`

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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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