Unique Node Question

[bonzaj]

hello

I've got a little problem with Maya API. Is there any way to retrieve some kind of unique id for each DG node? Node name together with path name will not work for me.

Here's what I've tried:

• making dynamic numeric attribute and attaching unique int to every node when it is created. It failed when performing mesh operations. ie. when triangulating, the copy of my mesh is created. It is an absolute copy (local dynamic attributes are recreated and their values copied). Unfortunetely this happens after addNode callback, so I don't have any control over it.

• making user defined data. It also failed when changing the mesh. Just before the mesh is copied, my user defined and self allocated attribute data is deleted, and after that maya recreates this data and takes it value from the source mesh.

• storing MObject of local dynamic MFnMessageAttribute. This is not unique -and the doc says that it should be unique (maybe node's MObject combined with MFnMessageAttribute MObject is unique??)

My current attempt is to make unique names of local dynamic attribute. I'll try to attach attributes of different names like:

(long name="uid234234",short name="uid")

There's a possibility that maya will fail to copy this attribute to the copy of my mesh. (It should fail because the copy will already have a short attribute name "uid"). Eventually (which is still possible) it will cause Maya to crash.

Please help me with attaching or retrieving unique information to/from node.

Thanks!

bonzaj

[joojaa]

Well the real question is whatkind of design actualy demands this? imena nodes arent supposed to intercommunicate (outside of dg thats what the cponnections are ther for). So theres no need for them to know anything of other nodes and thus will never get into problems with this.

Now then this has a tendency to point to bad design if you enlighten us with what you need it for then its possibe to redesign it NOT to need this.

[joojaa]

Oh if its a functor of somekind then it is possible to connect a callback to a node wich knows the node its connected to. BUt as is said this is a sortof indicator of bad or lacking design so...

[bonzaj]

thanks for your interest!

Hopefully I've managed to get it working - I used MObjectHandle to this - the doc says that It will hold MObject till all references exists. So this is what I wanted. And it's working .

Ok. I'll answer, on what I'm currently working, that I need such drastic decisions.
I'm making a tiny Maya core (which I called pico). I wanted to have a realtime preview inside of Maya of scenes that I was working with. The most importand thing was to get a 100% preview in Maya. So in order to do that I had to do some backwards engineering to rewrite most important parts of DAG, DG and attributes. Also there was a need to rewrite some of the most important internal nodes like "mesh", "transform", "shadingEngine", "surfaceShader" etc.

There were several problems when implementing the project. Ie when maya removes a node from DG it just moves that node to other "temporary deleted" node container. When the node comes back to DG it triggers the typical addNode callback. The problem is that this returning node has mixed up dagPath name, so I couldn't retrieve it properly from my "temporary deleted" container. Adding unique ID to each of the nodes helped me a lot, because I can comunicate between my nodes and maya nodes quite easly. Not saying that simple ID is a great hash improvement when searching the nodes in my DG.

I will answer for "What for?" question which may occure after my post .

It's for realtime demos development. You can find more info about the engine here:

http://www.devmaster.net/forums/showthread.php?t=4052

and the productions can be found here:

http://www.plastic-demo.org

Cheers!

[joojaa]

You are offcourse aware thet yoru breaking every design parameter in maya logic... And thus this leads to question is it maya anymore? So youd probebly get more out of thinsg otherwise.

Please note the the DG design is made by the best 3d minds of their time wich shows. since allmost no 3d dcc application has beat this design since then. So redoing it is lklike moving towards a worse maya not better.

Also remeber you do never own any data inside maya so you will prbably hit a wall at some point. eventualy.

CArtainly impressive if it works stably.

[joojaa]

Oh yeah one thing about mobjects... the handle wrapper is only a added security. BUt you shouldnt be holding on to mobjects for prolonged time, since they can be killed on whim by maya. Okay not when you sue mobjecthandles yoru enbnsured not to crash maya when it happens. Your in no way ENSURED the mobject will be the same on next invoke.

Okay seems like yoru having somekind of double book keeping going on in there. Its actualy hard to say since i dont know your eingene but ccouldnt deletion and udeletion be handled diffrerently? Imean is the overhead for yoru geme eingene so big that it cant recreate the info?

The relience on node id seem to suggest you sue ponters of somekind . Hoveerer i have a allternative solution for pointers inside the api (wich are in essence just a bad way of doing a dg connection) and they are connections, make a node that acts as a a database connector. THis has 3 main benefits:

1) it provides pointers taht are reliable insiccde maya structires, even renaming and rerouting is of no concern yetalone setting the state back on scene load.
2) All change messages can be handled eleganly. Also thsiway you need to develop less instead of more
3) the user can possibly edit the connections an dgraph them in mel if hee needs some trickery.

Now theres very little overhead here, plus maya knows how to reinstate the connecttion automaticaly . Then just make the connection axilliary so thet maya does not graph it.

I know many people dont usnderstand it but theese connections ARE mayas pointers. Not relying tehm is a bit working outside the dg and can cause BIG problems furtehr down the line.

[bonzaj]

this idea with uniqueIdManager node is nice one. I must say that It may solve my problems concerning undo/redo when deleting and internal copying of nodes.
The only problem would be in saving this node, because such manager should be rebuilded using addNode callbacks. But i think that it should be easy to solve this.
I'll implement it if necessary - I tested MObjectHandle on couple of big scenes (big in my environment ) and it worked stable.

I would also ask another question if you're familiar with my project's main goals.

Maya Bounding Boxes.

I've already rewritten lodGroup node. The main problem is in calculating bounding boxes in order to get a proper distance from the camera. I know that maya uses a bounding sphere over a bounding box to calculate a distance from an object to camera eye point. And everything is working ...

The problem is when the node has some dag children with their bBoxes. I thought that parent's bounding box is computed by calculating a box that contains all children boxes. And it seems that maya is working in such way. But only when you're not rotating. when the children are rotated arbitrary there are strange things happening to parent's bounding boxes which I couldn't understand. Please help .

[joojaa]

I dont think you need to worry about saving... the connections are saved and you may put teh callback on only afetter the save is done. Also i was thinking thet on load you could condense the node.

Anyway i recomend this method as its more mayalike atleats thats the way it seems to me (pleease do not ethe connections like this are invisibly/virtualy established to maya viewports, temporary with manipulators etc etc etc so that the dag works properly)

About the bb thing i must inestigate but i think its because the bb is allways considered in world orientation.

[bonzaj]

QUOTE(Joojaa @ 01/16/06, 10:48 PM) [snapback]225069[/snapback]
About the bb thing i must inestigate but i think its because the bb is allways considered in world orientation.

Thanks for checking! I think that the bBoxes are axis aligned in node's space. And while traversing towards the root they got world oriented (I think). Try to investigate the most simple example - a cube with a cube child, both of scale 1.0 and in the centre of the world. And then rotate.

Can I ask You one more question?

Do you write your posts in a speed of light or drink to much salmiakki?

[joojaa]

QUOTE(bonzaj @ 01/17/06, 12:33 AM) [snapback]225087[/snapback]
Do you write your posts in a speed of light or drink to much salmiakki?

Speed of light , salmiakki would actualy make my typography better. Because it would force me to drop speed.

[rob-bateman]

QUOTE(bonzaj @ 01/16/06, 02:33 PM) [snapback]225087[/snapback]
Thanks for checking! I think that the bBoxes are axis aligned in node's space. And while traversing towards the root they got world oriented (I think).

nope, they are always local to the transform - it may just be that your root is aligned to the x,y,z axes....