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type Transform = [
[number, number, number],
[number, number, number]

A transformation matrix is standard way in computer graphics to represent translation and rotation. These are the top two rows of a 3x3 matrix. The bottom row of the matrix is assumed to be [0, 0, 1]. This is known as an affine transform and is enough to represent translation, rotation, and skew.

The identity transform is [[1, 0, 0], [0, 1, 0]].

A translation matrix will typically look like:

[[1, 0, tx],
[0, 1, ty]]

and a rotation matrix will typically look like:

[[cos(angle), sin(angle), 0],
[-sin(angle), cos(angle), 0]]

Another way to think about this transform is as three vectors:

  • The x axis (t[0][0], t[1][0])
  • The y axis (t[0][1], t[1][1])
  • The translation offset (t[0][2], t[1][2])

The most common usage of the Transform matrix is the relativeTransform property. This particular usage of the matrix has a few additional restrictions. The translation offset can take on any value but we do enforce that the axis vectors are unit vectors (i.e. have length 1). The axes are not required to be at 90° angles to each other. More details in the relativeTransform properties page.