Mfnmesh Split And Update

[palmtree3141]

Alright,

In Maya 6.0, I call MFnMesh::split on a polygon and I get MS::kSuccess. However, the data MFnMesh gives me back about the mesh is still the same (i.e. it still gives me the same number of polys, other things are the same as before.) How do I get the mesh to "update." I've tried recreating the mesh from the dag path, still the same. MFnMesh::updateSurface doesn't seem to do anything.

PT

[daniel-faust]

Isn't it possible that you need to navigate to the newly created mesh? Probably you're still holding the original object that is in the construction history. Maybe that's it. On the other hand, "recreating the mesh from the dag path" sounds like you do ensure that you hold the last object in the history. Hmmm... maybe checking the Hypergraph will help (upstream and downstream connections enabled).

[palmtree3141]

By "recreate the mesh", I mean locally create a new MFnMesh from the dag path, if that wasn't clear. And will history be involved with this? I'm not using the Polygon Split tool; I'm calling a low level MFnMesh::split on the mesh data that does not save history (I can't undo it and there is nothing extra in the hypergraph with input/output connections turned on).

[rob-bateman]

If you want the history retained, you'll have to just create a poly split node and attach the mesh to it. Just calling and MFnMesh operations will only update the current mesh data - which will then be very quickly overwritten by the DG re-computing

[palmtree3141]

I do not want the history retained. I just want to call MFnMesh::split on this mesh and then be able to call split on polygons that are newly created by this original split, but now I cannot, as it appears that any MFnMesh is not in sync with its mesh data after the split. Is there any way to "force" a sync?

Thanks for all your insights so far. Rob, I was a fan of your website when I was learning the API. Very helpful.

[rob-bateman]

QUOTE(palmtree3141 @ 09/26/06, 05:15 AM) [snapback]248568[/snapback]
I do not want the history retained. I just want to call MFnMesh::split on this mesh and then be able to call split on polygons that are newly created by this original split...

The thing is, you do want the history to be maintained - whether or not history is generated for a scene is not something, you the plug-in developer, has the ability to define. The user determines that, so tough, you have no choice but to retain the history

QUOTE
....but now I cannot, as it appears that any MFnMesh is not in sync with its mesh data after the split. Is there any way to "force" a sync?

It is perfectly in sync, it's just that you've mis-understood what you're actually doing. Currently you have the knife to cut the mesh (MFnMesh::split), but each time you cut it, you are throwing the results away! Remember, each time you access an MObject mesh, it is not a mesh!! It is merely the state of some data at a certain point in the DG, at some given moment in time. You can manipulate that mesh data, however you are only manipulating temporary data - since the next time the DG gets evaluated, it will obliterate the changes that you made to that (temporary) Data.

To do this properly, you need to modify the DG graph so that your operations are stored entirely as a set of connected nodes in the Dependency Graph (so that on the next frame, the same operations are performed again and you still have some split polys). This is basically the crux of what history is in Maya, and everything you do to manipulate Maya's data from the API needs to be part of this history. There is no way around that i'm afraid, you've just got to bite the bullet and go with it.....

You'll notice for example that if you perform a poly split in mel, it inserts a node into the hierarchy. Within the API you need to do the same thing, it's just that the MFnMesh function set is operating on the raw data in the mesh node, as apposed to manipulating the connections between nodes to give you that result. So either, create a polyModifier node type in the API to perform the polySplit on an input mesh and write the result to an output mesh attr - or just use the relevant mel command which will be far simpler.....

QUOTE
Thanks for all your insights so far. Rob, I was a fan of your website when I was learning the API. Very helpful.

no probs

[rob-bateman]

just re-read one of your posts, you might need to clarify exactly what you are doing :

Q. when you say recreate the mesh via it's DAG path? Do you mean :

1. Create a new copy of the mesh and split the copied meshes data?
2. Modify a mesh to create a new bunch of polys on it?
3. Do something outside of the DG completely a just make a local copy of the mesh?

if 1, use MFnMesh::copy() before modifying the data
if 2, see above
if 3, see 1, then delete the mesh from the DG later on....

[palmtree3141]

I mean the mesh exists and I want to edit it. So even if i don't want a copy (I just want to split a few polygons on a mesh), I still have to copy the data to a new node before editing if I want the fnMesh data to update correctly so I can operate on the mesh again?

Thanks again!

PT

[rob-bateman]

ideally you want to create a polyModifier node to be inserted into the history of the mesh. If you just want to split a few polys, can you not select them and call a mel command to insert a polysplit node in there?