Python Driven Animation

Not everything can be keyframed, but almost everything can. There are benefits to keyframing, but it isn't always necessary. This short example shows how to use frame_change_pre handler, it is called on every frame change. This means if you have something you want to change as a function of time or frame number, that you can do this very easily. This works on text body too.

	import bpy
	import math
	# for demo it creates a cube if it doesn't exist,
	# but this can be any existing named object.
	if not 'Cube' in bpy.data.objects:
	bpy.ops.mesh.primitive_cube_add()
	frames_per_revolution = 120.0
	step_size = 2*math.pi / frames_per_revolution
	def set_object_location(n):
	x = math.sin(n) * 5
	y = math.cos(n) * 5
	z = 0.0
	ob = bpy.data.objects.get("Cube")
	ob.location = (x, y, z)
	# every frame change, this function is called.
	def my_handler(scene):
	frame = scene.frame_current
	n = frame % frames_per_revolution
	if n == 0:
	set_object_location(n)
	else:
	set_object_location(n*step_size)
	bpy.app.handlers.frame_change_pre.append(my_handler)

view raw frame_change_handler.py hosted with ❤ by GitHub

Search blender API docs for more information about frame_change_pre. You could even combine the frame_change_pre with setting and adding keyframes, but unless you want to export the animation - that might be overkill.

While debugging, you might find that you are calling successive versions of a function from the event handler. There might be more efficient ways of fixing this, but i've found this method removes 'old' code from the event handler list just fine.

	# if i ran the script twice, the functions are daisy-chained
	>> bpy.app.handlers.frame_change_pre
	[<function my_handler at 0x48a7d10>, <function my_handler at 0x5406490>]
	# this will removal all 'frame_change_pre' handlers,
	bpy.app.handlers.frame_change_pre.clear()
	# there are scenarios when you might want this, but sometimes it will be too broad.
	# one way to remove them is by doing a pop() on those items that match
	# the name of the function you want to remove, this needs to happen in reverse
	my_handler_list = bpy.app.handlers.frame_change_pre # alias
	fin = len(my_handler_list)
	for idx, func in enumerate(reversed(my_handler_list)):
	if func.__name__ == 'my_handler':
	my_handler_list.pop(fin-1-idx)

view raw remove handlers.py hosted with ❤ by GitHub