Maya Api: Share An Object Between Nodes (with Pointer)

[sleepyfox]

hi,

without having tried it (maybe I can save myself a lot of trouble and time). Has anybody tried to share an object with another node over a pointer or some kind of reference?

I have a MPxLocaterNode which holds some attributes and a non-maya object (array of floats - just some random vertex data). This pointarray get rendered to the viewport through some openGL calls by the draw() method of the MPxLocaterNode.

My question is: Is it possible to separate the rendering function and the data and share the vertex data between them?

I'd like to use the MPxLocaterNode just for the drawing purpose and use a MPxNode otherwise (for attributes and vertex data) without the need of copying the data. Can I pass the pointer of the non-maya object (in MPxNode) to another node (MPxLocatorNode)?

I can't pass it to the other node as an attribute (because it isn't an attribtue).

thanks

alex

[uiron]

to my understanding, what you're trying to do goes against node architecture - node needs to hold everything it needs to implement it's behaviour, all external data should come from IO attributes.

not really an API expert, but that vertex array could be plugin-wide DLL global, accessible by all plugin code - this way your nodes can reference that shared data.

[sleepyfox]

thanks for the quick answer!

QUOTE
goes against node architecture - node needs to hold everything it needs to implement it's behaviour

yes, I know it's against policy but I need to/want to source some of the calculation out of maya (or at least out of maya-objects)

QUOTE
all external data should come from IO attributes.

but some of the data is not feasibly transferable over attributes. Especially if the data is some non-maya object. or is there a way of exposing custom non-maya objects to another node as a plug?

QUOTE
but that vertex array could be plugin-wide DLL global, accessible by all plugin code

maybe.. I try to avoid global variables if possible (plus, I got adviced that maya likes to crash if using them).

The only other possible solution (known to me) is to drop the idea of two nodes and put everything into one...

kind regards,

alex

[rob-bateman]

QUOTE(sleepyfox @ 04/15/09, 08:22 AM) [snapback]305845[/snapback]
but I need to/want to source some of the calculation out of maya (or at least out of maya-objects)

[input attrs] -> [compute: call external lib] -> [store in output attrs]

Not so hard to do....

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some of the data is not feasibly transferable over attributes.

I don't believe you.

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or is there a way of exposing custom non-maya objects to another node as a plug?

Yes. You write a node to expose it's attributes as, well, attributes.

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maybe.. I try to avoid global variables if possible (plus, I got adviced that maya likes to crash if using them).

That would have been me.

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The only other possible solution (known to me) is to drop the idea of two nodes and put everything into one...

http://www.highend3d.com/boards/index.php?showtopic=242667

[joojaa]

QUOTE
The only other possible solution (known to me) is to drop the idea of two nodes and put everything into one...

Describe the problem. Thing is trasfeeral ofd data is very invisible. Even huge amounts of data move freely about the node tree. Maya doenst necceserily go around copying the data, not as such maya may read the data form the plugs directly as if they were pointers, its hard to know for sure.

QUOTE
or is there a way of exposing custom non-maya objects to another node as a plug?

Yes offcourse you make it a composite attribute.

[sleepyfox]

QUOTE
[input attrs] -> [compute: call external lib] -> [store in output attrs]
Not so hard to do....

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some of the data is not feasibly transferable over attributes. - I don't believe you.

ok I wasn't clear enough about this point... or maybe (most certainly) my understanding of attributes is false... i thought only Mayas built-in types (numeric, mesh, string, sphere etc.) are supported.

can I transfer _anything_ over an attribute?
If so, I revoke everything said/written und state the opposite (as we in germany say).

example:

I have a class "someObject". This gets created and initialized in a node as an object (no attribute, not static, just a "normal" object). So this node holds a pointer to this object and can access its values. I can't (or at least I think I can't) make an attribute from it, cause its type (someObject) is not supported by maya. Or how do I expose it? Which type is it.

I can put the type in another node and make this node the type of the attribute, but how can I access the data of this new node (which encapsulates someObject)?

thanks lot for the advice!

[joojaa]

QUOTE(sleepyfox @ 04/15/09, 08:39 PM) [snapback]305858[/snapback]
can I transfer _anything_ over an attribute?

yes _everything_ a computer does is just a numeric type.

QUOTE
I have a class "someObject". This gets created and initialized in a node as an object (no attribute, not static, just a "normal" object). So this node holds a pointer to this object and can access its values. I can't (or at least I think I can't) make an attribute from it, cause its type (someObject) is not supported by maya. Or how do I expose it? Which type is it.

A class contains something, the purpose of maya api is for you to describe that something to maya. So what your class eats is whet you should describe. Yes that means possibly a lot of work but thats what you have set out to do.

Maya doesn't necessarily need to know what the lib does just everything the lib needs inserted to get it going.

[sleepyfox]

QUOTE
yes _everything_ a computer does is just a numeric type.

in the end they are all bits, of course
my question was, if the attributes are restricted to the maya built-in types, or can I pass every object (without reformating).

The object is (or can be) very very large and I don`t want to put it in a maya container, so maya can use it.
The data needs to be in a certain order in a certain format to be calculated very quickly so I can't rewrite it for maya or reformat it every time the node wants to recalculate it.

Bottomline is that I dont believe (and thats just an assumption) that maya can handle that data (its a large array for physix simulation) as nodes and all the data as attributes feasibly. Sure I could use mayas pointarray and this and that and reformat the data so it fits well with the nodes, but this imho would be slowdown in simulation speed.

I just wanna use maya for visual feedback, setting the scene and rendering.. but the simulation itself should take place outside of maya.

I think I will try to use one node for everything, so I dont have all the problems with sharing of objects etc. after rethinking it I think it s no drawback after all.

I just for fun I will try my luck with getting the pointer to a node and missusing it - though I got warned of "the ungodly abuse of the DG" I have in mind

[joojaa]

QUOTE(sleepyfox @ 04/15/09, 11:43 PM) [snapback]305887[/snapback]
Bottomline is that I don`t believe

I do

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its a large array for physix simulation

I have pushed arrays and trees in the size of 1-2 Gigabytes no problem.

So eaxactly how much is yoru large 5 Gigabytes?

[rob-bateman]

QUOTE(sleepyfox @ 04/15/09, 12:43 PM) [snapback]305887[/snapback]
Bottomline is that I dont believe (and thats just an assumption) that maya can handle that data (its a large array for physix simulation) as nodes and all the data as attributes feasibly. Sure I could use mayas pointarray and this and that and reformat the data so it fits well with the nodes, but this imho would be slowdown in simulation speed.

You are making assumptions and that's dangerous with the Maya API. Thing is, you quickly learn that the architects behind maya knew what they were doing, and had thought of these problems. As such, they kindly added the MPxData class that lets you define your own data chunks that can be passed through attribute connections (which is how mesh's, nurbs surfaces etc get passed as attribute connections through the DG). Ideally try not to use it if possible, and prefer exposing the actual data as much as possible. It may be required for something like an NxActor pointer or some other user data (in cases where you want successive modifications to a physics entity), but again you could simply write a node that exposed the NxActor's parameters.

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I just wanna use maya for visual feedback, setting the scene and rendering.. but the simulation itself should take place outside of maya.

That's fine, but in the long run it's better if you don't optimise anything for performance and accept the hit of exposing the data as attributes. Ultimately maya can be extremely useful in aiding debugging and testing (since you can view and edit all data in the AE), and realistically stepping a physics engine (such as physX) doesn't take that long to compute when compared to say, rendering the data in openGL. The bottom line is that exposing a physics engine to a node and attribute system is going to maybe half your framerate, but the advantages in being able to view, edit and debug your data set will very quickly outweigh the disadvantages. FYI, this is what i've been doing for the last 4 years or so at work. It really isn't as much of a performance killer as you seem to think.

[sleepyfox]

maybe I m assuming too much problems using the maya api in the way it s ment to be used.
It s too bad that there s no guide which explains every detail of the api (ok, there s the whitepaper but it covers not every aspect), how everything works together with a deeper insight of the working (at least the documentation is complete :-).

I ll try to heed your advice and try to do it all in the MPxLocator node with a custom MPxData object.

thanks again for the advice!

[joojaa]

QUOTE(sleepyfox @ 04/16/09, 05:32 PM) [snapback]305943[/snapback]
how everything works together with a deeper insight of the working

No documentation can pass experience, insight or intelligence. You have to supply that form out of yourself. If on the other hand you could than this wouldn't be the first problem to solve.

[sleepyfox]

It