Save and Restore

In one of the previous lessons, we learned to apply several transforms. But how do we remove the transforms, after we are done using them?

Reverse a transformation

It is possible to reverse a transform, by applying the inverse transform. For example, if we apply a translation (a, b), we can reverse it by applying a second translation (-a, -b), which puts us back where we started. We can reverse a scaling factor s, by applying a second scaling factor of 1/s. We can also reverse a rotation through an angle a by rotating through angle -a.

However, we often need to apply two transformations: translate and rotate. These must be removed in the reverse order;inverse rotate, followed by inverse translate. This gets tedious and, often, leads to fragile code.