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Vector to rotation matrix

Started by Mulligan Sep 12, 2006 at 12:52 AM 2 replies 850+ views

Original Post

Sep 12, 2006 at 12:52 AM

I have a xbox 360 controller and want to take the 2d coordinate that represents the current thumbsrick orientation, and make a rotation matrix that will rotate a sprite on the screen to face the same way as the thumbstick. The coordinate ranges for the thumbstick are -1.0 to 1.0 for both X and Y. For whatever reason, this is stumping me, and I'd like to know how to do it. If I could convert the point into radians, it would solve my problem too, but I can't figure out how.... Thanks

Numsgil

Sep 12, 2006 at 1:56 AM

If you divide the thumbstick coordinates to get the slope (y/x) you can then feed that into an arctan function to get the radian measures. You'll need to check which hemisphere you are in still, since arctain goes -pi/2 to pi/2. You can do this by checking the sign of x and using that to add pi to the degrees if x is < 0.

Then you need to double check that you are in the range 0 to 2 pi.

Then you need to watch for the case when x = 0 or you'll get a divide by 0.

It's not the greatest solution by any stretch of the imagination, but it gets the job done, and it's easy to conceptualize with even the basest of trigonometry skill.

Mulligan

Sep 12, 2006 at 2:08 AM

perfect, works well.

Thanks

haegarr

Sep 12, 2006 at 3:17 AM

Don't know whether the API you are using provides it, but all these case distinctions are already wrapped into a function called atan2 (perhaps Numsgil knows that it doesn't exist for the xbox). The function is to be invoked as atan2(y,x) and normally results in the range [-pi,+pi], so perhaps you may be lucky with atan2(y,x)+PI.

[Edited by - haegarr on September 12, 2006 3:17:53 AM]

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