Extending render capabilities for built-in shape nodes

[oweber]

I am interested in adding a few visualization capabilities to a Mesh shape node.

For example, I would like to add an option to draw small arrows on the mesh faces that corresponds to some vector field.

I know that this can be done by implementing a user defined shape node. However, this is a pain and I am looking for a quick solution. I basically don't need too much customability so writing a user node seems an over kill.

Also, in general, is it possible to obtain direct access to opengl render commands without having a custom node?

Say I want to write a user command that when invoked, render a triangle onto the viewport. Is that possible?

[joojaa]

it possible to obtain direct access to opengl render commands without having a custom node?

No.

render a triangle onto the viewport. Is that possible?

Yes you can do that just make a mesh shape and make the triangle there, then just mark the object as reference*. Or you use a particle system etc etc.** Visualisation is after all what the software is about, just not openGL.

However, this is a pain

Pain is relative, if you feel that opengl, or indeed the api at all is the way to go then i can assure you working with a shape is much more closer to the way your brain works and significantly less painful as a result. But me i would do it in mel in 10 minutes with nodes intead. YMMV.

• you can put many shapes under one trensform, this makes most 90% users unaware of the visualisation node. And even then the 10% of users wou could figure this out might not notice untill they actually investigate further.

** there is a nifty trick hereyou can make the shape just a point and then use a CGFX or HSLS shader to drive the shape if you wish to be really obscure this has the advantage of being just as fast as anything you could do with the api.

[oweber]

Thanks Joojaa!

When I say writing shape node is a pain I mean that it takes a lot of time.
If I want everything to be customized then it is a great way to go.
However, in my case, I basically need a mesh with all the built in features and one small extra feature.
So it will be a waist to implement all the functionality that Maya Meshes already have.

Adding another shape node under the transform sounds like a good hack.
However, I want to draw little arrow on each face (there are a lot of faces).
Can I do it with a single extra shape/mesh? Or do I need an extra mesh for each arrow?
If arrow is too much hassle, I can  get  along with just a small line segment (like Maya visualize normals).

BTW, how can you use 10 lines of MEL code to get that?
Will I need to loop over all faces? That along could be very slow.

Thanks! 

[joojaa]

Well thats what poke and particle systems are for, no loop.

[oweber]

Can you please elaborate? I couldn't find anything related to poke and particles in the forum.

[oweber]

it possible to obtain direct access to opengl render commands without having a custom node?

No.

I just bumped into M3dView:beginGL().

Is something like that could work (say, as part of a command)?

   M3dView view = M3dView::active3dView(&stat);

   view.beginGL();

   //do reder stuff here

   view.endGL(); 

[joojaa]

Is something like that could work (say, as part of a command)?

Perhaps but you would be overriden the second maya updates, which would be the second you do something*. Whets the actual problem with doing a node? I mean its not any extra work compared since most fo teh code is boilerplate anyway. I mean a MPXlocator node is in fact just ~30 lines of extra code (on top on your command init), plusyour ogl stuff on top.

Are you trying to circumvent the fact that you dont have enough (or any) node ID's?

Anyway since you WANT to use opengl ill look into hakeing a example, but to be honest the devkit has good examples allready and my delivery time at the moment is months.

Can you please elaborate? I couldn't find anything related to poke and particles in the forum.

Err try reading the maya manual, or looking into maya menuitems

• whch is why if you do anything in maya api its going to be a node most likely.

[joojaa]

Damn deleted your post by mistake sorry about that.

Actually, maybe I can derive from Mesh and add a custom render phase on top of the existing draw.
Will that work?

You dont have the right thing to inherit. Its a api it does not expose internals just externals to what they want you to have.

What I meant was that I don't see how this can help to avoid loops and in particular to do what I need by using MEL.

You insert a poke node to get points at centers of faces, then you connect the output of that to a particle node thets located preferably under the same transform as your object (yhis creates a particle object wiith particles at each point + centers). Then attach a instancer to that particle, and make all points less than the id number of original points in mesh size to 0 (with a particle expression), then use some suitable way to drive the remaining particle instances orientation. Note for this to be fast you need the visialized data to be available in a node with same offset and type as particles use, or as a texture or whatever.*

*yes you still need a node, you cant do anything meaningful in maya without nodes.