[Bf-committers] Introduction to Notifiers

[Elia Sarti]

Hi, nice docs!

Speaking of notifiers, I'd like to point out one small issue that yet 
can be annoying and probably not quick to solve. Currently UI regions 
(in most editors) are scriptified, in essence allowing people to 
edit/remove/add properties from these views (one example is rigging 
interfaces).

These properties of course update correctly when you edit them from the 
UI region itself but often don't when you edit the property directly at 
the RNA level.
This is related to how notifiers work: you have the listener for the UI 
region and this determines when to do updates but the problem is that by 
adding panels/properties to the region from py you can't really guess C 
side what updates are needed and often you end up not having properties 
update correctly.

One solution could be that every property displayed in the UI region 
could make the UI region "inherit" its notifiers (those you pass to 
RNA_def_property_update) and react to those in its listener.
The idea here is, if property "extra_info" when edited needs to send a 
NC_OBJECT|NA_EDITED notifier and I'm displaying this "extra_info" 
property, then when I see a NC_OBJECT|NA_EDITED notifier I should 
refresh the view because it is *likely* that the edited property was 
indeed "extra_info". I know this sounds bad and indeed it is, also from 
a performance stand point, because it's too generic, but would be 
automatic at least.

In this case in fact I don't think py listeners really are a solution, 
as these should be specified for each panel which it's not optimal.

Another, probably even worse, solution could be to add some type of 
"update hook" to RNA where basically you can add a handler for when 
properties pertaining to a certain ID or ID type are edited and act 
consequently.

I understand this is not a big issue right now which is why I never 
thought of bringing it up. Although it could be annoying in some cases. 
For instance if you have a rigging interface with a property in the UI 
that represents the local position of a bone control, moving the slider 
should update the bone's position but also moving the bone should update 
the slider as expected.


Matt Ebb wrote, on 02/05/2010 12:48 PM:
> Hi all,
>
> I've noticed in IRC over the past months, a little confusion about
> what notifiers are and how they work in Blender 2.5. I've
> compiled/written up a little tutorial that hopefully explains their
> purpose a bit better for new coders.
>
> Check it here: http://wiki.blender.org/index.php/BlenderDev/Blender2.5/NotifiersIntroduction
>
> (Or any corrections, please edit the page :)
>
> As I was doing a bit of work in the wiki I also noticed a
> not-very-widely publicised doc on adding new properties with DNA and
> RNA. I'd encourage people unfamiliar with it to take a look:
>
> http://wiki.blender.org/index.php/BlenderDev/Blender2.5/DefineProperty
>
>
> cheers,
>
> Matt
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