gEDA-dev: [pcb] multiple hids in one .so

[DJ Delorie]

> All callbacks that don't have gc param.

That's what I wanted to avoid.  It's overkill for all the built-in
hids.

> 1. let's say PCB will never be multithreaded so using global variables in
> the API is ok (like it uses gui now). In this case the GUI hids should set
> a global var pointing to the selected HID. I'm not sure this would be a
> smaller patch but it would look worse :)

It's kinda what we do now, we just don't set gui for exporters until
after we're in redraw.

> 2. let's pass HID to _all_ calls and the drawing ones would extract gc
> from the HID structure. It's more work but would make the interface more
> orthogonal.

There are many gc's for each hid; you can't extract the right gc from
a hid.

> 3. Add a set_hid() callback that would inform the .so which hid is
> selected. Called only once, before any other hid function. Probably this
> is the less painful to add, but it seems like some workaround.

The core of pcb doesn't know about shared objects, so this is the same
solution as #1.