I have been working on a project that extensively make uses of glMatrix, a javascript library which implements a number of extremely handy methods for manipulating vectors, quaternions and affine matrices.
To set the scene:
- root scene consists of two objects, which relative to the world coordinates
- object A has a single transform, which consists of translation component
- object B has a single transform, which consists of translation, rotation and isotropic scaling
- default camera has no rotation component
My desired outcome is to apply a rotation to the camera to view object B in its native orientation.
As I have transformation matrix of object B, I thought I could use the mat4.getRotation method. Apply it to the camera and we should be done.
To my dismay, this method result in a view of B that is slightly non aligned.
I played around with a few other ideas, for example:
- perhaps the 3D framework I was using is rotation the scene, rather than the camera?
- how about getting the inverse of the matrix, and try again?
- the fact that
glMatrixuses column major convention, does that affect anything? getRotationmethod returns a non-normalized quaternion. (this turns out to be related to the issue I am having)
I banged my head for a good half a day, and looked up glmatrix getrotation does not work on google, and lo and behold, first search result mat4.getRotation is not working when the matrix was scaled with specific vectors.
So all I had to do is to scale the transform matrix before calling getRotation, and it worked like a charm.
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