[g-a-devel]Accessibility module loading

[Michael Meeks <michael ximian com>]

* The Current state of affairs

	Currently accessibility information is loaded on the basis of
the user setting a GTK_MODULES environment variable before they
execute the program. This has the following problems:

	- User needs to know which libraries an app uses to whack the
	  names of the peer libraries into GTK_MODULES

	- A blanket GTK_MODULES setup causes galloping inefficiency -
	  lots of libraries being pulled into a Gtk+ app unneccessarily

	- Bad bonobo-activation support, components won't pick this up

	- Accessibility support is not dynamicaly changeable ( ok so
	  this is a demo feature I know :-)


* What we can do about it

	So; here is how I propose we fix it:

	The GnomeProgram (libgnome/gnome-program.c) initialization
setup allows for module information to be passed in; this is excellent
since it gives us a set of GnomeModuleRequirements for each
application.

	Thus - if enabled [1] it would be possible to grok each of
these modules and load any approriate ancilliary accessibility
libraries as neccessary.

	Having determined which modules we wish to load; we would hook
the 'gnome_accessibility_module_init' entry point, I propose two of
these:

	void gnome_accessibility_module_init     (void)
	void gnome_accessibility_module_shutdown (void)

	The 'shutdown' method is hooked up to a GConf listener on the
accessibility key - so that we can disable accessibility in-place.


* How does this affect the capabilities ?

	+ Gnome apps no longer need to rely on GTK_MODULES
	+ We can easily locate the correct modules - no redundant libs
	  need to be linked
	+ Bonobo-activation support is fine - working via the GConf key
	+ Accessibility is dynamicaly alterable leading to funky demos.


* What API changes are neccessary ?


	No API changes neccessary; unless the change:

-    gpointer expansion1, expansion2;
+    const char  *prefix;
+    gpointer     expansion1;

	counts.


* What needs doing ?

	+ libgnome/gnome-program updates.
	+ add new gail / at-bridge entry points.
	+ guard gail / at-bridge against double inits


* Other approaches and points

	- Simply make libgnome depend on at-spi and put link
	  vs. the at-bridge always - not attractive due to at-spi
	  code / API churn.

	- Link accessibility always everywhere - again adding
	  rather a lot of code that is not strictly neccessary.

	- couldn't this module implemented extremely abstractly
	  providing an amazing framework for other similar
	  things; - not attractive; more complex, less readable
	  and there's no time right now.

	- but this will mean Gtk+ only programs suck more for
	  accessibility you'll still have to export GTK_MODULES.
	  True; use the Gnome platform wherever possible, or re-invent it
	  endlessly.

* Notes

[1] - I propose that we have something like:

	if (have_non_empty_env_var ("GNOME_ACCESSIBILITY"))
           enable = get_boolean_from_env_var (~);
	else
	   enable = gconf_get_key ("some_magic_path");

[2] - To do this really well, we need to ram the 'prefix' of each
module into the GnomeModuleInfo structure; I propose using the
'expansion1' element for this; and preferably renaming this to
'prefix' - since this information is generaly useful. This (optional)
rename constitutes the most minor of API changes.


-- 
 mmeeks gnu org  <><, Pseudo Engineer, itinerant idiot