There is one more very important reason that I didn't touch on
before about why you wouldn't want to invert the CTM in order to
get back to identity -- the context may not have started out with
the identity transformation.
HIView sets up your context such that the CTM gives you a
coordinate system that looks like Quickdraw. Take the inverse of
the CTM and you will get the default coordinate system instead of
the Quickdraw one you may be expecting.
Additionally, there is Resolution Independence. This is generally
implemented in the frameworks by scaling the CGContext
appropriately -- inverting the CTM will defeat this feature.
Someday when your users have control over this feature they will
run your application and wonder why some of the drawing is tiny :).
I wasn't expecting that one would reset the transform
inappropriately. There could be cases where you're nested down
several save/transform/restore levels and need to get back to the
identity transform do perform an operation before continuing on with
the current transform.
Particularly if you own the context, HIView and/or Resolution
Independence issues shouldn't be an issue -within- that context, at
least in this context. :-)
steve
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