You do not have to do all the view drawing in the same coordinate
system. Also repeatedly transforming the paths you are drawing
does not seem like the best approach. Better to save and restore
graphics state to draw the bits in different coordinate systems,
so your graphics model objects can be static. Your -drawRect
would look conceptually like this:
One thing about your method that's not immediately obvious to me is
why it's more efficient to apply all these transforms to the entire
coordinate system of a view than just rotate a bezier path within
the view. It seems like, at least intuitively, that transforming a
small part of a view (the hands) would be much more efficient.
Ken
It is more efficient to modify the graphics state, because that is a
dynamic operation. Part of the graphics state is a transform which
is applied to anything drawn into that state. When you use -concat
on an NSAffineTransform object, all you are doing is modifying the
graphics state transform; it has no immediate effect, it just alters
anything which is drawn after that by transforming the drawing
differently. On the other hand, when you apply a transform to an
NSBezierPath object, every set of coordinates stored in that path are
modified by the transform and replaced with the new transformed
coordinates. So it is more efficient to combine all your coordinate
system transformations so they happen dynamically in the final draw
operations into the graphics state, where a transform is always going
to occur anyway.
