Advertisement Jump to content
knsl96

Constraining rotation to a single axis

Recommended Posts

Advertisement

One way to do it:

If the user input is a quaternion, convert it to axis and angle.

Convert axis and angle to a rotation vector: vec3 rv = axis * angle

Project this vector to your constraint axis unit vector: vec3 constrained_rv = constraintAxis * constraintAxis.Dot(rv);

Then convert result back to axis / angle: float angle = constrained_rv.Length(); vec3 axis = constrained_rv / angle;

Then convert to quat or matrix or whatever you need: quat q; q.FromaxisAndAngle(axis, angle);

 

So that's quite simple. I assume everything is given in global space, otherwise perform the operations in the local space of the joint for example.

Ask if there's something unclear...

 

Share this post


Link to post
Share on other sites
22 minutes ago, knsl96 said:

float dprod = constraintAxis.Dot(constraintAxis, rv);

This line already gives the angle, so no need to calculate magnitude later. But that's just an optimization.

 

Pretty sure the NaN happens here if angle is zero:

24 minutes ago, knsl96 said:

MyVector axis = new MyVector(constrained_rv._x / angle, constrained_rv._y / angle, constrained_rv._z / angle); 

So you would need to return identity quaternion if angle is close to zero before that.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Advertisement
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

GameDev.net is your game development community. Create an account for your GameDev Portfolio and participate in the largest developer community in the games industry.

Sign me up!