GNOME.org
 

Re: inaccessible treeviews and tables

Hello,

no, your problem is not related at all with that thread. The problem I
pointed on that thread was solved (take into account that that thread
has almost 2 years old).

On Glib every class (GObject) has a given GType (see  [1][2]). For the
task that you are doing, take as reference gtkcellrenderertext and
gtktextcellaccessible.h. In this case "text" is the "custom" cell
renderer I was talking about. As usual (usual glib boilerplate for
C-code), gtktextcellaccessible define some macros related to the new
type. One is GTK_TYPE_CELL_ACCESSIBLE, that points to an also new method
gtk_text_cell_accessible_get_type. In general, when you declare a new
GType, you need to provide a method that returns this new GType. In
order to provide the implementation of that method, right now there is
some utility macros like G_DEFINE_TYPE [3].

In summary, what GtkTextAccessible does is declare
GTK_TYPE_CELL_ACCESSIBLE and gtk_text_accessible_get_type on his header,
use G_DEFINE_TYPE to implement the get_type method on his source code.
Then GtkCellRendererText calls
gtk_cell_renderer_class_set_accessible_type using GTK_TYPE_CELL_ACCESSIBLE.

So, for the case of C, you have some examples of how to do this. The
different is that custom cell renderer is written on Vala. Being as it
is Vala, when created the equivalent C-code, all this would be the same,
so it is really likely that you would be able to get the GType from a
class that you are defining (in this case this ContactListCellRenderer
accessible class). Unfourtunately, my experience with Vala is zero. I
just know what it is. So I would not be able to tell you how to do that.
In any case, #vala channel at Gimpnet seems full of people. Probably
they could help you.

About your question in relation to init methods: GObjects are an Object
Oriented add-on to C, so they need to do some manual handling in order
to register the type and create the new object and class. You can find a
detaile information here [4], but probably for now you can just forget
that, and just follow the rules. That method needs to be called on the
class_init method. Take a look to what GtkTextAccessible and
GtkCellRendererText are doing. Those are an example of a custom cell
renderer and his accessible object.

Best regards

[1] https://developer.gnome.org/gobject/stable/
[2] https://developer.gnome.org/glib/2.40/
[3]
https://developer.gnome.org/gobject/stable/gobject-Type-Information.html#G-DEFINE-TYPE:CAPS
[4]
https://developer.gnome.org/gobject/2.40/chapter-gobject.html#gobject-instantiation

On 07/08/2014 08:36 AM, Peter Vágner wrote:

Hello,
I have subclassed GTKRendererCellAccessible, implemented basic
get_name method in my subclass taking advantage of reference to the
CellRenderer.
However what I am unable to workout is how do I get a proper GType of
my subclass so I can pass it to the
gtk_cell_renderer_class_set_accessible_type () on my CellRenderer
subclass. I assumed I am missing something verry obvious but I then
went back to the earlier discussion you pointed me to a while ago...
https://mail.gnome.org/archives/gtk-devel-list/2012-August/msg00050.html
. I can find no method get_type or similar on GTKRenderCellAccessible
either directly implemented nor inherited. So either I am missing
something simple or this is more complicated than I might imagine.
Also the help text for gtk_cell_renderer_class_set_accessible_type ()
states it's advised to call this from the init method on the
CellRenderer. I am afraid this is really basic and I might be able to
research it else where but what is an init method in this case? Is
that a constructor or a method called init? I haven't see no method
like this while looking at the GTK docs.

I apologize for taking your time but I am really interested in being
able to do this.

Greetings

Peter

On 07.07.2014 16:47, Piñeiro wrote:

Good catch, I didn't realize that ContactListCellRenderer. Sorry, I'm
not used to search through Vala source code.

Looking at that code, there is a variable called "entry", that in most
cases is the contact. On render_name it uses that variable to get the
name. On render_userstatus it uses that variable to render the status. A
ContactListCellRendererAccessible would need to use this "entry"
variable to expose the name and status on a custom implementation of
AtkObject.get_name and AtkObject.ref_state_set.

Looking for
https://developer.gnome.org/accessibility-devel-guide/stable/gad-custom.html.en

has two problems:
    * It is outdated.
    * It is intended as a guide to extend widgets accessibility. A cell
renderer is not a widget.

What do you mean for gtk_get_accessible? AFAIK, that method call doesn't
exists. There is a public gtk_widget_get_accessible that returns and
accessible type, and a private one
_gtk_cell_renderer_get_accessible_type, that returns a type.

Subclassing GtkTreeViewColumn will not get anything. As explained, it is
the cell renderer the one that gets the focus and renders the content,
the problem there is about the custom cell renderer.

So, in summary, and based on your comments and a quick look on the code,
what it is needed to do here is:

  * Create a new subclass of GtkRendererCellAccessible something like,
ContactListCellRendererAccessible
  * Call gtk_cell_renderer_class_set_accessible_type on
ContactListCellRenderer class_init method.
  * Reimplement AtkObject.get_name and AtkObject.ref_state_set on
ContactListCellRendererAccessible, using that "entry" variable to get
the information

Thanks for all this work

Best regards

On 07/07/2014 04:07 PM, Peter Vágner wrote:

Hello,
Issue in transmission-gtk is just my guess I haven't yet tryed to
tinker with its source code so I may really be absolutelly wrong with
my assumption.
Venom developers are subclassing GTK_CellRenderer here
https://github.com/naxuroqa/Venom/blob/master/src/ui/ContactListCellRenderer.vala

. I can see they are also using GtkCellRendererText in order to change
a GTK_COMBOBOX which remains accessible here
https://github.com/naxuroqa/Venom/blob/master/src/ui/ContactListWindow.vala

.
While creating my CustomCellRendererAccessible do I really have to do
everything that is recommended here
https://developer.gnome.org/accessibility-devel-guide/stable/gad-custom.html.en

? As I said I have tried to retrieve a coresponding accessible by
calling gtk_get_accessible(MyCustomCellRendererObject). I was able to
manipulate that accessible and set its name and description however by
testing with orca I have discovered changes I am trying to make result
in changes to the parent object treeview in this case not individual
rows which as I understand are represented by the CustomCellRenderer.
Then I have tried to subclass a GTK_TreeViewColumn where the
CustomCellRenderer is connected to by trying to create empty
ATK_Object, overridding Get_Accessible() in my subclass. Of course
this does not work. I haven't really understood where is the problem
however I think It is just not possible to instantiate ATK_Object like
all the other objects using new operator.

So Now I am lost again and I have no idea on how to possibly move
forward. Frankly I don't feel confortable following the article Making
Custom Components Accessible on the gnome developers wiki, it's why I
have started exploring these things on my own hopefully asking more
concrete questions. The only lesson I have learned so far is that I
really need CustomCellRendererAccessible. But I don't have an idea on
how to do that.

Thanks your patience and helpfull hints.


Greetings

Peter

On 07.07.2014 14:02, Piñeiro wrote:

Hi,

I will try to answer your question as best as I can.

As you say, sometimes a 3rd party gtk app developer creates a custom
cell renderer in order to add some new visual stuff. The accessibility
related are not skipped. The already in place cell renderer
accessibility is used. But if the new cell renderer uses something
totally different to render text, then the gtk+ cell render accessible
object would not be valid. In that case you would need to provide a
custom accessibility object for that custom cell renderer. For the
rest
of this email, I will call them CustomCellRenderer and
CustomCellRendererAccessible

gtk_cell_renderer_class_set_accessible_type, is just the method that
relates a cell renderer with his accessible method. Is just a utility
method to avoid the need to redefine the method get_accessible for any
custom object. So for this case, once you have a
CustomCellRendererAccessible, you would need to call
gtk_cell_renderer_class_set_accessible_type on your
CustomCellRenderer.

About caring on CellRenderer: as I said, there is already an
accessibility support of CellRenderer. So probably you just need to
focus on that CustomCellRenderer, where the information about name and
state are stored there (that would be the difference with a "vanilla"
CellRenderer), and then try to expose it via a
CustomCellRenderAccessible.

About that transmission-gtk: after a quick look on Venom. I don't see
any custom cell renderer being created. As far as I see, they are
using
GtkCellRendererText, that should be already supported. Are you sure
that
in that case you are under a custom cell renderer problem?

Best regards

[1] https://developer.gnome.org/gtk3/3.12/GtkCellRendererText.html

On 07/05/2014 06:20 PM, Peter Vágner wrote:

Hello,
A while ago I was trying to get some understanding on how to make 3rt
party gtk apps accessible. At that time Alejandro Piñeiro pointed me
to some docs and bugzilla entries describing the current situation.
Unfortunatelly I haven't still mastered that. I have at least
realized
and hopefully understood at least some verry basic things related to
this.
For example currently I am able to set accessible labels and I am
able
to add / tweak relations between labels and the interactive controls
they are supposed to label. I know this is not a big deal but I have
already tweaked an app or two this way and I know it works fine.
Another thing what's currently on my radar are widgets that are often
reported as tables or treeviews. Individual rows appear to be
keyboard
focusable however orca is unable to report their role and text.
I guess the common scenario is that the app developers tend to
subclass Gtk.CellRenderer to create more visually appealing
design. In
this case if I understand correctly the content is directly drawn to
the widget surface and proper accessibility related properties are
skipped from the implementation entirely.
By reading gtk reference docs I have came accross a method
gtk_cell_renderer_class_set_accessible_type () . That appears to be
only info I was able to find related to Gtk.CellRenderer and
accessibility. Can anyone please give me a hint so I might try move
forward and try learning how to implement accessibility for a widget
where Gtk.CellRenderer is used?
Do I need to care about Gtk.CellRenderer or should I just set
accessibility related properties such as label and description for
the
affected widgets without looking at Gtk.CellRenderer? How do I refer
to multiple treeview colums or table cells in such implementation? Is
there an app or just a code example I should look into to see this in
action?
I have seen widgets with incomplete accessibility like this in many
apps but if my explanation is not accurate enough here are two from
the top of my head. One is the list of torrents in the
transmission-gtk svn://svn.transmissionbt.com/Transmission/trunk and
the other is a contact list widget in a gtk3 based tox client called
venom https://github.com/naxuroqa/Venom .
I will be looking into this some more, it may take me a while like it
took me ages to figure out and get used to labelling and related
stuff
so I am just trying maybe with some hint I might master it better
this
time.

Thanks

Peter

_______________________________________________
gnome-accessibility-list mailing list
gnome-accessibility-list gnome org
https://mail.gnome.org/mailman/listinfo/gnome-accessibility-list







-- 
----
Alejandro Piñeiro
[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]