Quaternion in Game Development.

Newbie & Debugging Questions
#1

Hi,

I am new here. I have a quick questions.
How come most of the books that I have read use matrix for game development, not quaternion?
Is quaternion the fastest way to work with today?

Thanks.

#2

Well you still need a normal matrix for many other applications. Quaternions are only good for rotation

#3

I keep thinking that it can replace many things in the matrix. Are you sure that it is only good for the rotation part of the matrix?

#4

Yep

#5

Technically, you can also use a quaternion to represent scaling.
But this complicates everything else, since any rotation transformations can only be meaningfully performed on unit quaternions. So if you work with non-unit quaternions to represent scaling, whenever you want to apply a rotation to it, you would have to normalize it (requires a square root), do the rotation transformation, and then scale back again by the original length.

#6

I see. That was what I found from reading Jmonkey basic tutorial as well.

Thank you so much.

#7

On quaternions and scaling…yeah probably not worthwhile computationally. The math’s all wrong though. The issue is if you convert to a matrix…the conversion code is assuming that it’s a unit quaternion.

#8

Oh, you’re right. Thanks! That was a good hint. I gotta go change some code…
Representing uniform scaling in a quaternion works nicely when the conversion as layed out here is used (the matrix representation right before the sentence “since qwqw + qxqx+ qzqz+ qyqy = 1 this gives”).
Apparently, one also does not need to renormalize the quaternion when applying any rotations. This is really nice. Applying uniform scaling to any quaternion is then just scalar-multiplying by sqrt(scaleFactor).

#9

Yeap. Since rotation is P’ = QPQ-1 (which eliminates any scale factors) or QPQ* which will scale by magnitude of Q squared and these compose as expected.