this works by tagging functions, eg:
def my_func(scene):
pass
bpy.app.handlers.permanent_tag(my_func, True) # <-- important bit
bpy.app.handlers.frame_change_pre.append(my_func)
* Adds two new python handlers: scene_update_pre() and scene_update_post()
These run before and after Blender does a scene update on making modifications
to the scene.
* Datablocks now have an is_updated property. This will be set to true in the
above callbacks if the datablock was tagged to be updated. This works for the
most common datablocks used for rendering: object, material, world, lamsp,
texture, mesh, curve.
* Datablock collections also have an is_updated property. If this is set, it
means one datablock of this type was added, removed or modified. It's also
useful as a quick check to avoid looping over all datablocks.
* RenderEngine.view_update() can also check these properties, for interactive
viewport rendering.
http://wiki.blender.org/index.php/Dev:2.6/Source/Render/UpdateAPI
from Jesse Kaukonen (gekko)
--- text from the patch.
Recently Campbell Barton added callback functionality for Python's usage, but this only includes pre- and post-render callbacks. There are no callbacks for the duration of the render. This patch adds the few lines required for executing a callback while Blender Render is working. The callback resides in the rendering pipeline stats function, so whenever statistics are printed, the callback is executed. This functionality is required if one wants to:
1) Observe what is happening while Blender is rendering via the command line
2) Add custom statistics that Blender prints while the renderer works
3) The user wants to continue executing his Python script without the code halting at bpy.ops.render.render()
Personally I'm currently using this for printing out more detailed progress reports at Renderfarm.fi (such as CPU time, time spent rendering, total progress in regards to the entire rendering process). Tested on Windows, Linux and OS X.
Example on how to use the callback:
def statscall(context): print("Thanks for calling!")
bpy.app.handlers.render_stats.append(statscall)
bpy.ops.render.render(animation=False, write_still=True)
Python:
* adds bpy.app.handlers which contains lists, each for an event type:
render_pre, render_post, load_pre, load_post, save_pre, save_post
* each list item needs to be a callable object which takes 1 argument (the ID).
* callbacks are cleared on file load.
Example:
def MyFunc(scene): print("Callback:", data)
bpy.app.handlers.render_post.append(MyFunc)
C:
* This patch adds a generic C callback api which is currently only used by python.
* Unlike python callbacks these are not cleared on file load.
