Honestly, you'll just have to set them up again. In almost all cases
this will be cheaper than inverting the CTM to, and you can always
try to rearrange your drawing order to avoid having to setup a lot of
state each time.
Set them again to what values? The context parameters might be set
by the outside code (e.g. written by other team) so at the point
where you need to do this you just don't know them (e.g. you are a
plugin and there is no easy way to "rearrange" the drawing order).
And there are no getters for most (or all?) context parameters
(e.g. the above mentioned alpha) to be able to grab them all and
reset them later... Besides, when your code (e.g. a plugin) first
gets the context, the context might already have a non-identity CTM...
