🚀 go-pugleaf

I would like to be able display a tiff image which can be resized and
zoomed.  I know how to resize the image using the scale to fit example,
but what is the best way to zoom in on a portion of the image?  Should I
use canvas::clip_rect() and then scale the clipped region with
canvas::transform()?

Also, is there any documentaion on canvas::push_transform(), 
canvas::push_clipping(), and related methods?  ScaleToFit uses
push_transform() but it is not clear what it is doing.  Could someone
post a brief description about what these functions are for?

Thanks for any help!
John