AS3: Getting the scale of a Matrix object

Question

Most often, questions are asked about how to scale a DisplayObject, and the answer is usually to use a Matrix.

My question is, how to you GET the scale of a Matrix (

Answer 1

Generally, a reliable way to isolate the scaling component in a matrix is to use the matrix in question to transform the unit vectors along the axes, and then measure the length of the resulting vectors.

For instance, given the transform from a DisplayObject, and using the Matrix3D, the scaleX would be obtained as follows:

transform.matrix3D.deltaTransformVector(Vector3D.X_AXIS).length

Or, if you use the concatenated 2D Matrix, the scaleY would be:

transform.concatenatedMatrix.deltaTransformPoint(new Point(0,1)).length

Note that the deltaTransform* functions ignore the translation effects of the matrices, which have no effect on the scaling.