Forcing Node Update

[korchkidu]

Hi everybody,

I made a custom node with an input attribute made internal. When I connect this input attribute to some other attribute, setInternalValueInContext is not always called because Maya sees it as useless somehow. How could I do force the setInternalValueInContext to be called every time?

Best regards.
K.

[joojaa]

QUOTE(Korchkidu @ 06/10/09, 05:58 PM) [snapback]309237[/snapback]
I made a custom node with an input attribute made internal. When I connect this input attribute to some other attribute, setInternalValueInContext is not always called because Maya sees it as useless somehow.

Well simply put you shoudl never ever design a node that has something like this. Its very clear and simple. IF a node has a attribute it must be meaningful to SOME output, if not then you dont need it. So if you dont have any meanifull output the dirty does not do anything if dirt doesent do anything you dont update and your node is useless.

So either you missed some critical part of the affect network or you deesigned the thing wrong.

QUOTE
Maya sees it as useless somehow.

That is usually a implication of the fact that you missed something fundamental. Chek you affects network.

QUOTE(Korchkidu @ 06/10/09, 05:58 PM) [snapback]309237[/snapback]
How could I do force the setInternalValueInContext to be called every time?

Ugh.. that would be pointless its as if taking maya a chucking it to the garbage bin.

Ask for the value somewhere, no really you should not ever be in this position. It simply means thres a flaw in your design intent. You can force it but then why use a node in first place, if a event is what your after?

My advice is go back to paper and draw the sequence of your chain. and see where you missed the gap. I sounds harsh but its the difference between a gem and a pig.

[korchkidu]

Thanks for your answer.

I know that my node "seems" useless to maya but it is usefull to me;). My node is only an external interface to some c++ object I implemented. So basically, I want to be able to access my C++ objects through maya interface. As we already discussed in another thread, it is not possible for me to put everything into maya. To put it simply, we have tens of C++ classes and only some of them are useful for the user. I want to expose their interfaces to maya. So I made a custom node for each of these class and expose their public members using attributes.

So, yes, my node does nothing into maya. That is why I have some trouble. I know that it is not perfectly maya-compliant but our program is quite big and it would take months to put everything the way it should be so it is a compromise.

K.

[korchkidu]

HI,

just some clarification about what I want to do. Basically, I want to retrieve the translate information from some transform in the scene and set an internal C++ Object of mine. So,

1) I create an MPxNode containing a pointer to my C++ object ;
2) I connected the translate attribute of the transform of interest to my MPxNode;

So, now, what I want, is when I translate the transform, it updates my internal C++ object:

| Maya Transform | -translate------translate-> | Custom Node .....MyObject *_object->SetTranslate(translate)...... |

What I tried but maybe I made some mistakes:
1) setInternal. logically, it does not get called everytime because Maya sees my node as useless because it has no output.
2) Adding an attributeChanged callback. Well, it is not called when the transform is translated;
3) Adding an nodeDirtyPlug callback. It seems that when retrieving the plug value, it is the outdated value.

Please help. Any idea of what I am doing wrong? I am not a full time maya programmer so please be simple (and nice^^).

K.

[hansesurfer]

what I would try is to make a fake attributeAffects in your node with an output attribute and connect another transform to that output attribute.

does this make sense to you?

[joojaa]

QUOTE
just some clarification about what I want to do. Basically, I want to retrieve the translate information from some transform in the scene and set an internal C++ Object of mine.

Well ok then your not after a node! Your after a event! Now you can bind events into your node BUt best just bind events out.

But really this blows mayas pipe.

See when maya does anything it triggers events. maya potentially triggers a lot of events. This can slow maya to CRAWL, seriously your comfy 20-50fps things depend on this not being done.

QUOTE
Adding an attributeChanged callback. Well, it is not called when the transform is translated;

Yes maya suspends the full network updating while it is in a tool mode. Theres not much you can do about that. What you should use is the MPxNode:: setDependentsDirty or

Now this gets called when you get informed the plug got marked up for compute.

You can then set up a message thet it got changed to your own code. But beware its not advisable to compute a lot here just pass messages. Ideally youd just pass a message saying well yes you know it got changed then update at next convieniant redraw or so, later in anycase to avid a huge cascade of updates during a very short timespan of doing.

Or even better you should implement it as a locator that draws nothing. Thisway you will get a chance to draw your locator just liek you were a shape.

A alternate solution would be to make the node thread safe and do the computation by force.

QUOTE
? I am not a full time maya programmer so please be simple (and nice^^).

It odes not matter much, either you play ball with maya or you do not. In either case maya has a a additional thing in nodes.

QUOTE
, it updates my internal C++ object:

Yes but irrespectuively if the node is a gui or not maya will send out a LOT of events and potenttially your update will just eat up 50-99% of your performance. So does your c object realy need to update real time. Would it not be enough to update on dirty each 1/10 of a second or so. Thsi would save maya form supending redraw just because you like to update every time maya does something. Trust me its very easy to swamp even the most powerful computer with something like this.

So even if you now think you want to force you might come to the conclusion you dont want later. Ive cetaily found out that theres NEVER EVER A GOOD TIME TO FORE MAYA TO UPDATE on events, no matter how hard i try to find one reason to do so. Trust me ive been thinking 5 years.

[joojaa]

Oh one more note

QUOTE
Adding an nodeDirtyPlug callback. It seems that when retrieving the plug value, it is the outdated value.

And it should. The data gets fetched nly when the compute cycle gets initiated and the entire graph refreshes bottom up. So the act of asking for it in COMPUTE fetches and computes the value along the chain.So inorder to get a valuye you will need to manually mine it form the output plug. Which itself wont be clean unless it has some sane output

You can force the update with the functions in MPlug

MAya just simply dont work from nodes down it works in oppsite direction the last ndoe in chain being the master.

PS: having a dummy node in way or making a shape are way better solutions than trying to force. Its a PAIN IN TH BUTT because your doing exactly what they told you not to ever under any circumstances do. (and yes they designed it so that this would be painfull)

[korchkidu]

Hi,

thanks a lot for your answers. So to summarize, there are 3 solutions:

1) Use events. Well, as Joojaa said, it is not a good solution as maya triggers a lot of them. So, as advised by Joojaa, I will avoid it.
2) Connect a forceUpdate output attribute to some input of a transform. This solution seems easy to implement. I will give it a try;
3) Make a locator. This solution seems the cleanest to me. As in essence, my custom is some kind of locator but driven by another node.

Thanks a lot for your help. I will try both solutions and let you know.

Best regards.

K.

[joojaa]

QUOTE(Korchkidu @ 06/12/09, 03:12 PM) [snapback]309362[/snapback]
3) Make a locator. This solution seems the cleanest to me. As in essence, my custom is some kind of locator but driven by another node.

Yes locators and shapes are by nature last thing in mayas graph and they do initiate automatically when dirty a update. But not immediately when the dirty triggers but rather in a orderly fashion that makes maya not bunch up into a traffic jam.

Hmm... maybe for simplicity one could ask autodesk to implement a mechnism saying i want a last node in chain type node? Well perhaps not, youd get some unimaginably bad kludge.

[hansesurfer]

I also would suggst make it a locator first as its an update starting point itself upon scene refresh.

QUOTE
But not immediately when the dirty triggers but rather in a orderly fashion that makes maya not bunch up into a traffic jam.

joojaa, where the heck do you know that from?

[korchkidu]

Hi,

It works perfectly well now. Thanks again for your help !

Best regards.
K.

[joojaa]

QUOTE(hansesurfer @ 06/12/09, 03:30 PM) [snapback]309364[/snapback]
joojaa, where the heck do you know that from?

Its how push and pull networks work. In any case i do regulary trace this, so that i do is i print the entire sequence of how the plugs update/dirty and they do update in perfectly logical orderly fashion as long as there isnt any one node to disrupt the flow (if there is performance sinks very low).

Anyway it makes sense since theres 2 phases dirty up phase and the compute. So the whole dirty up happens first before the compute stats this means all thing that got dirty are now collected up so they all update on same refresh, and no stuff gets half and half computed on seprate refreshes. So its cached for optimal update, and no node that does not need to update gets updated.

This also ensures no plug gets updated 2 times during the compute phase in normal circumstance.