Attribute Change Updates Particle's

[clockwise9]

Okay, I have read the Maya docs, and many of the posts on here about the updating of Maya's DG Nodes, and how and why it works (to some degree...I'm fairly new with the API). But, I'm asking the question in hope to find an answer to my problem.

I have successfully created an MPxEmitterNode that reads data from a file for particle creation (or will, it's hard coded at the moment). Basically the way it works is on the start time of the particles the emitter will create the particles, and on any frame after, it will update the existing particle positions. Somewhat similar to Next Limit's RealFlow Plugin, except that the amount of particles doesn't change.

I have created an attribute within the emitter called "path". This will basically be a directory which I will read all the data from for particle creation and updates.

The problem I'm having is that I want to be able to change the input directory/file on the fly. The user can update this interactively because I have added the attribute to the attribute editor using an AE Template. (Same functionallity as a file texture).

To make this work I added an attributeAffects call within the emitter node that looks like the following

 attributeAffects(m\_aPath,mOutput)
      m\_aPath is my path Attribute
      mOutput is the emitters output to the particle system.

So, the way it works now is if I change the filename, nothing is updated. This would make sense because Maya, from what I understand, won't update the particles until the time changes again, and at that point the file path will have changed.

Now the Question.....
Is there a way to re-evaluate a particle system, when a specific attribute changes, and is this bad programming practice or not within the API.

I guess I would of thought that the emitters compute function would be called with the mOutput plug when I changed the filename (m_aPath attribute), but it's not.

Could I add a dummy attribute, and have that plug call the same part of the compute function?...(That's me just thinking out loud now)

Cheers!
Justin

[joojaa]

QUOTE(rosenj4 @ 09/15/06, 06:59 AM) [snapback]247563[/snapback]
So, the way it works now is if I change the filename, nothing is updated. This would make sense because Maya, from what I understand, won't update the particles until the time changes again, and at that point the file path will have changed.

No it should update immediately, the on frame update only applies to dynamic simulation wich you shouldnt be implementing here. But your problem is that your using a emission node, wich is a dynamic simulation, wich is exactly what you dont want.

See emission only affects creation of particles they are then pushed to the particle node, wich means they are no longer in your node. So unless you allways set a particles lifespan to 1 frame then your filename change in middle of animation would still only affect emission , form frames forward of that frame.

[clockwise9]

Hey, Thanks for the reply!

QUOTE
No it should update immediately, the on frame update only applies to dynamic simulation wich you shouldnt be implementing here. But your problem is that your using a emission node, wich is a dynamic simulation, wich is exactly what you dont want.

Okay, so are you saying I should be using a custom node to deal with particle interaction? and not an emitter? Unfortunately I'll need some more convincing as one of the leading particle simulation software developers (Realflow) use this exact model to import their data.

QUOTE
See emission only affects creation of particles they are then pushed to the particle node, wich means they are no longer in your node. So unless you allways set a particles lifespan to 1 frame then your filename change in middle of animation would still only affect emission , form frames forward of that frame.

By this do you mean that there is no way to update the particle Shape at the time of the filename change? Because I'm dealing with the emitter that is not actually outputing anymore particles?

Basically the way my emitter works is

if its the first frame

create some points and send to particle node for creation

any other frame

traverse DG to get particle shape
get position vector array
update values
update plug

I guess you could say I've extended an emitter node to act as a data interpreter.

And this part does work....

The only problem is when I alter something in the attribute editor. The update doesn't take effect until the emitter runs it's compute function again.

Now I know that each node should only be aware of itself (it's own attributes), and I'm probably breaking the API's architecture paradigm by doing this. But in that case, in what way can I deal with particles and external data if the API doesn't let me extend a particle node?

Cheers!
Justin

[joojaa]

QUOTE
Okay, so are you saying I should be using a custom node to deal with particle interaction? and not an emitter? Unfortunately I'll need some more convincing as one of the leading particle simulation software developers (Realflow) use this exact model to import their data.

No, but you cant break design rules just beacuse somone else uswes different design ruiles.

QUOTE(rosenj4 @ 09/15/06, 09:50 AM) [snapback]247570[/snapback]
Now I know that each node should only be aware of itself (it's own attributes), and I'm probably breaking the API's architecture paradigm by doing this. But in that case, in what way can I deal with particles and external data if the API doesn't let me extend a particle node?

Yes tahst why you shouldnt be implementing just a basic emitter wich is ONLY reserved for emission, you shoudl be impleneting something that acts on the particle data itself. Emitter is certainly not out of teh question for the class your looking for per see.

You shoudlnt traverse the dg, but thing is any ndoe can directrly manipulate the partilce array plugs wich are just that lists of arrays. Because if you have no connections maya has no way of knowing whan stuff is duirty thus will never update untill time changes. But you can connect to thsioe arrays instead wich is much simpler.

THing is if you ditched being a api traversal and actyed one the right dg connections your values would update whan you needed. Take a look on how array mapper works! then implement something between arraymapper and a emitter.

QUOTE
if its the first frame

create some points and send to particle node for creation

any other frame

traverse DG to get particle shape
get position vector array
update values
update plug

thats just your problem:

This is how dg works wich is why you cant skip the point where you make connections.

Fame changes your emitters time changes it gets marked dirty, particle shapes time changes it gets marked dirty, because its a shape it gets requested so it asks for your emitter to do its stuff becuase it dependent on it, now all updates.

You change values in your emitter! nothing happens bacuse theres no communication form your emitter to the particle shape. Maya des not push the answer it pull

[joojaa]

Heres a mel example that illustrates the problem:

CODE
file -f -new;
$p1=particle -p 0.0960585 0 6.555466 -p 2.552413 0 5.912484 -p 3.865097 0 6.01901 -p 5.417792 0 8.103921 -p 3.846244 0 7.771651 -p 1.177108 0 7.391317 -p 0.496784 0 9.288065 -p -3.912957 0 8.875907 -c 1;
$p2=particle -p -2.303541 0 -2.838957 -p -4.596647 0 -3.075808 -p -3.269049 0 -7.28051 -p -1.545864 0 -4.526251 -p -0.557834 0 -4.431884 -p 1.925458 0 -4.265348 -p 3.412438 0 -0.227993 -p -5.957696 0 -3.5;
addAttr -ln MoveUp -at double  $p1[0];
setAttr -e -keyable true ($p1[0]+".MoveUp");
addAttr -ln MoveUp -at double  $p2[0];
setAttr -e -keyable true ($p2[0]+".MoveUp");
//nondirect connection wich si what you have
dynExpression -s "vector $pos0=particleShape1.position0;\r\nfloat $move=getAttr particle1.MoveUp;\r\nparticleShape1.position=<>;" -rbd particleShape1;
//direct connection updates on change!
dynExpression -s "vector $pos0=particleShape2.pos0;\r\nparticleShape2.position=<>;" -rbd $p2[0];
currentTime 2;

If you see both particles have MoveUp added to them but ionly the other readas it trough a direct connection so the other uipdates allways and the other on time change.

Make sure the lines are uncut

Anyway the firts particle shape relies on mel to acces the vartiable, it goreas ahead and reads teh variable (api writes stuff ina way thets not promotiing unless you broadcast it, unlike mels setattr), this ilustrates what happens whan you cut teh flow of things.

[clockwise9]

QUOTE
You shoudlnt traverse the dg, but thing is any ndoe can directrly manipulate the partilce array plugs wich are just that lists of arrays. Because if you have no connections maya has no way of knowing whan stuff is duirty thus will never update untill time changes. But you can connect to thsioe arrays instead wich is much simpler.

THing is if you ditched being a api traversal and actyed one the right dg connections your values would update whan you needed. Take a look on how array mapper works! then implement something between arraymapper and a emitter.

Okay, so the reason I went this way (Using the emitter), is because I hit a wall when trying to create Vector arrays, and connecting them to a particles position.

You can view my other post on the topic here.

Connecting Attributes Directly into Particles

If I can get around this issue, and connect it directly that would be perfect. But if you take a look at the previous post, I'm not so sure I can. I'll have to look more into the Array Mapper and the previous issues I had as my understanding of the API has increased.

I did however noticed the error it gave me saying I should use an arrayMapper, but I think I found some problems in going that way.

QUOTE
If you intentionalty want to get blood form your nose do this: mark the array attribute dirty whan yoru done.

I know I shouldn't do this, but if I wanted to... what would the syntax be?

Anyway, I'm up for any ideas

Cheers!
Justin

[joojaa]

yes but the advice is dcefferebnt because the description is different.