[Bf-animsys] Animation logic

[Joshua Leung]

Hi Erick,

For a useful (though overly broad/general) introduction to the key concepts
of how updates in Blender happen in general, see this:
https://wiki.blender.org/index.php/Dev:2.5/Source/Architecture/Window_Manager


Here you go  (this was originally go to be "in short", but then it turned
out to be a lot longer reply ;):
* The code in your "operator" modifies the keyframes/etc. data (i.e. stuff
stored in the SDNA structs that form that Main database)
* When your operator is done, it sends a "notifier"  -
WM_event_add_notifier(C, ....notifier flags..., NULL);
  For keyframe editing, this is usually something like NC_ANIMATION |
ND_KEYFRAME | NA_EDITED (i.e. notifier for "animation context", "keyframe
data", "editing performed/action").
* Notifiers are added to a global queue to be processed the next time we go
through flushing updates (more about this below), instead of being handled
immediately (i.e. the "callback" style of updates that other toolkits -
notably Qt, GTK, and all of the Java ones - Swing, etc. use. However, the
"callback style" has some serious disadvantages - i.e. some updates
happening multiple times, bad performance if you inadvertently chain up a
bunch of these by relying on delegating to other callbacks, and "callback
hell" if that chaining accidentally forms a loop.)
* As in any GUI program, Blender has what's known as an "event loop".
Basically, it's like you've got a piece of code in your main function that
does:
  while (true) {
        get_event();
        handle_event();    // run operators, and/or exit the program
        flush_updates();   // handle notifiers
        refresh_and_redraw();
   }

  In Blender, notifiers are handled in the "flush_updates()" step, after
the operator runs (i.e. handle_event() == an operator gets run, or some
event gets sent to the UI handler, or something like that). What that means
is that it goes through each window -> editor -> region, and for each of
the queued up notifiers, it asks those if it would like to do anything
about that notifier. (You could say it's sort of Observer Pattern stuff I
guess, except it's deferred updates, and we're still really only asking if
they'd like to do any updates). So, each of the animation editors will
listen for NC_ANIMATION | ND_KEYFRAME events, and when they hear them, will
tag themselves to be redrawn.

  Finally, when it's time to redraw the UI, only the editors/regions that
are tagged to get redrawn will be redrawn (since redrawing everything all
the time, even if nothing has changed is slow, and would make everything
laggy). So, at this point, all the visible animation editors would get
redrawn, because they tagged themselves to get redrawn, in response to the
notifier that got sent out.



Now, all of the above is only just updating the UI (which is what your
question was about). If you were to talk about how you get those animation
changes flushed to the actual models and rigs, then you'll need to be
talking about the dependency graph stuff then. But, there it's really a
similar idea again :)


(Also, if you're just concerned with the transform code, have a look in
transform_generics.c -> recalcData() for how things get tagged for updates
there :)



Regards,
Joshua


On Tue, Apr 19, 2016 at 7:19 PM, Erick Blender <erickblender at gmail.com>
wrote:

> Hi there!
>
> Wanted to ask about Blender animation logic, how graph editor, timeline,
> dopesheet and NLA work together?
> Reading code files in blender/editor/animation i find many useful code and
> i found as well  that in blender/editor/transform/transform_conversion.c
> there is basic keyframes move, ...
>
> My question is how graph editor, timeline, dopesheet and NLA talk to each
> other for example when moving a keyframe in graph it get updated in the
> dopesheet or vise versa. Is there some where in the code that Blender
> update dopesheet when action happening in the graph editor?
>
> Thanks in advance :)
>
>
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