[cairo] How to draw paths with different registration points?

[Chris Wilson]

On Fri, 29 Jan 2010 02:55:27 -0800 (PST), Stuart Axon <stuaxo2 at yahoo.com> wrote:
>    In the Shoebot project were implementing the Nodebox api using Cairo.  
> I wonder if anyone on the cairo list would know how we can implement something:
> 
> Nodebox lets you set the registration point of paths drawn 
> (when you draw a shape in NB it creates a path)
> 
> This is set using the transform mode, which can change during the script:
> 
> transform(mode=CORNER)
> In this case the current cursor position is the top-left of any path that will be drawn.
> 
> transform(mode=CENTER)
> In this case the current cursor position is the middle of any path that will be drawn.
> 
> Any ideas ?

This is how I would approach this problem, given a path constructed
outside of my control (forgive the pseudo Python):

  draw_path(cr)

  extents = cr.path_extents()
  path = cr.copy_path()
  cr.save()
  cr.translate(compute_offset(extents, MODE))
  cr.new_path()
  cr.append_path(path)
  cr.restore()

This does presume that the PyCairo has wrapped paths to hide their ugly C
nature...
-ickle

-- 
Chris Wilson, Intel Open Source Technology Centre