Your wikipedia link reminds me that I should have listed rotation, scaling, shear, and reflection transformations. Oops. In your second link, I like the trick

Your wikipedia link reminds me that I should have listed rotation, scaling, shear, and reflection transformations. Oops. In your second link, I like the trick of storing positions as [x, y, z, 1] and directions as [vx, vy, vz, 0]. Regarding, "Hey, Markus! How come this matrix is 4x4?", I'm not sure if Markus was referring to an affine transformation, part of a perspective projection, a matrix representation of a quaternion, or something else. The mere fact a matrix is 4x4 (or some other size) unfortunately doesn't say much about what it's meant to do. Which probably contributes to Markus getting so many questions.