K-3D

On 10/22/2010 09:13 PM, fink wrote:

> #no crash if the following line is commented out
> k3d.property.connect(doc, camera_position.get_property("output_matrix"), \
>     camera.get_property("input_matrix"))

While K-3D should be able to handle this without crashing (I'm looking
into why it doesn't), this code probably isn't doing what you want -
connecting a node output to one of its inputs is never the right thing
to do - it's the equivalent of an infinite loop.

Cheers,
Tim

> this code probably isn't doing what
> you want -
> connecting a node output to one of its inputs is never the
> right thing
> to do - it's the equivalent of an infinite loop.


Thanks for the explanation. K-3D is fascinating, and it's great to find a use for everything I forgot from multivariate calc & linear algebra!

The `camera_position` node is a FrozenMatrix node, and `camera` is a Camera node. Is the infinite loop created because of a special property of the FrozenMatrix?

The code in question is adapted from k3d/tests/testing.py:
"""
def create_camera(document):
	camera_view = k3d.plugin.create("ViewMatrix", document)
	camera_view.position = k3d.translate3(k3d.vector3(-10, -15, 10))
	camera_view.look = k3d.identity3()
	camera_view.up = k3d.translate3(k3d.vector3(0, 0, 20))
	
	camera = k3d.plugin.create("Camera", document)
	k3d.property.connect(document, camera_view.get_property("output_matrix"), camera.get_property("input_matrix"))

	return camera
"""

I was playing around, trying to determine what it does (no comments/docstrings!), and then boom, crash.

On 25 October 2010 03:01, Timothy M. Shead <tshead@...> wrote:

> On 10/22/2010 09:13 PM, fink wrote:
>
> > #no crash if the following line is commented out
> > k3d.property.connect(doc, camera_position.get_property("output_matrix"),
> \
> >     camera.get_property("input_matrix"))
>
> While K-3D should be able to handle this without crashing (I'm looking
> into why it doesn't), this code probably isn't doing what you want -
> connecting a node output to one of its inputs is never the right thing
> to do - it's the equivalent of an infinite loop.
>
> Cheers,
> Tim



Hi Tim,

would infinite loops be sane if they were clocked? If such a loop is created
then a special node is created and inserted with it's function been to only
pass on events about property changes every T seconds?

On 10/24/2010 11:46 AM, fink wrote:
>> this code probably isn't doing what
>> you want -
>> connecting a node output to one of its inputs is never the
>> right thing
>> to do - it's the equivalent of an infinite loop.
> 
> 
> Thanks for the explanation. K-3D is fascinating, and it's great to find a use for everything I forgot from multivariate calc & linear algebra!
> 
> The `camera_position` node is a FrozenMatrix node, and `camera` is a Camera node. Is the infinite loop created because of a special property of the FrozenMatrix?

Actually, disregard my last - I thought I saw "camera" twice ...

Cheers,
Tim

On 10/24/2010 02:54 PM, Daniel Scott Matthews wrote:

> Hi Tim,
> 
> would infinite loops be sane if they were clocked? If such a loop is
> created then a special node is created and inserted with it's function
> been to only pass on events about property changes every T seconds?

See my followup - fink's use-case wasn't actually a loop.  Regardless,
we already handle this case, by automatically detecting loops when a
property is evaluated - if you have a loop, the property returns its
internal value.

Cheers,
Tim

On 10/22/2010 09:13 PM, fink wrote:
> I've tried the code below in 0.8.0.1 release, and 0.8.0.2 from hg, on multiple computers, and K-3D crashes on execution for both. Does it do the same for you?
> 
> 
> """
> #python
> 
> import k3d
> doc = context.document
> 
> camera_name = "Camera Top"
> camera_pos = (0, 0, 10)
> camera = k3d.plugin.create("Camera", doc)
> camera.name = camera_name
> camera_position = k3d.plugin.create("FrozenMatrix", doc)
> camera_position.matrix = k3d.translate3(camera_pos)
> #no crash if the following line is commented out
> k3d.property.connect(doc, camera_position.get_property("output_matrix"), \
>     camera.get_property("input_matrix"))
> existing = k3d.node.lookup_one(doc, camera_name)
> doc.delete_node(existing)
> """

So, I've been poking at this off-and-on.  It seems that the crash only
happens when deleting a node that has property connections, with
undo-redo disabled.  So you could fix this in a couple of ways: first,
you don't need to make property connections just to position the camera,
you could do:

#python
import k3d
camera = k3d.plugin.create("Camera", context.document)
camera.name = "Camera Top"
camera.input_matrix = k3d.translate3((0, 0, 10))

Second, you could enable the undo/redo mechanism when you delete your
camera:

...
context.document.start_change_set()
doc.delete_node(camera)
context.document.finish_change_set("Delete top camera")

... this essentially duplicates what happens when you delete something
through the UI, and explains why we haven't noticed this problem there.
 It's a good idea to make your scripts undoable anyway, to be a good
citizen.

Cheers,
Tim