Thanks David 
I did a quick little test to make sure, and yes, it is possible to use this constraint on a cloned object. And since cloned objects have their own kinematic state, they can move independently of the original.
So in principal, it can be done, but I’m not too sure about the specifics of your request. Would you mind elaborating a bit?
Here’s the workflow I was thinking about:
Say, for example, you have an airplane fuselage and you want to put some rivets along the various section seams. It would be great to be able to select one of the edges as a path, then invoke your tool, select a rivet model and have your tool create instances of that along the edge. Options would include total number divided evenly, number per point span, or something like that.
The second with was to be able to do the same thing on a surface. In that case, you’d select the surface, invoke your tool, choose the model and then choose setting with regard to number of instances and placement randomization. Say, for example, 0% randomization places the instances in a perfect array, whereas 100% places them totally randomly. (Of course no two instances would ever be placed at the same point.) 
Does that make more sense?
It does make a lot of sense actually.
I think I have an idea. It’s not exactly what you want, but it would probably be more general, and hopefully more useful. I’ll see if I can run a few tests this weekend.
I have a feeling that something very usefull will come from this.
Thanks again ShaderOp…for all your effort.
That’s exactly the kind of stuff that ICE does really well at And would be a lot leaner than generating a ton of geometry or N instances instead of a single point cloud of size N.
Say, for example, you have an airplane fuselage and you want to put some rivets along the various section seams. It would be great to be able to select one of the edges as a path, then invoke your tool, select a rivet model and have your tool create instances of that along the edge. Options would include total number divided evenly, number per point span, or something like that.
An offset value would be good also.
That is my number one issue…how to have the best of Nurbs, Solids and Polygons(SubD’s) modeling in one place.
In several CAD packages it is possible to use a line to do that easily , even with History and follow any later change in surface topology.
Don’t thank me yet. I already have one failed idea under my belt
Anyways, the idea I had in mind was trying to find a way to constrain an object to a mesh, but use the UV coordinates of the mesh to control the constrained object’s position. Sort of like the built-in surface constraint, but for polygonal meshes.
To better illustrate my point, here’s what can already be done with the built-in surface constraint:
If the same thing can be done with polygonal meshes, then it would be a lot more flexible, since a polygon mesh can have multiple UV maps and you can lay them out however you please.
So if this hypothetical constraint existed, you would need to specify the constraining geometry and the UV map, and then just animate or position objects by changing the UV coordinates on the constraint.
That’s the idea I had in mind, but it’s not easy to implement. Biggest issue is mapping a point on the UV map to the corresponding position on the mesh’s surface. There’s away to obtain the UV coordinates from the XYZ coordinates on a surface (sort of at least), but not the other way around. At least none that I could find in the SDK.
Thoughts? Ideas?
I have no thoughts on how to achieve that, but if you can pull it off you’ll be my hero of 2009.
I think an issue could be that it’s not a 1-to-1 relationship between uv and xyz .
an xyz coordinate maps to only one uv coordinate per uv set, but not the other way around.
Then again, you could just pick the first xyz the inverse lookup finds, assuming the uv has been built in a way anyway that no multiple xyzs are intended:D
The inv. lookup will be surely tricky to write though, especially when it comes to subdivs!
ps- ShaderOp I hope U don’t mind I added your addons to my resource listing website rray.de/xsi. Let me know and I’ll remove them right away!
ps I’ ve just read about curvature in your post, this reminded me some curvature related stuff can be found here too rray.de/xsi
ray
Of course I don’t mind! If anything, I’m grateful for all the work you’re doing to keep that list up to date.
Wouldn’t this approach limit the “randomness” to only where a UV existed? It seems to me that unless the mesh was extremely dense, it might be pretty easy to spot the UV pattern. Imagine a grid of 8 by 8. If you then applied some rivets to that based on the UV map, would they end up scattered along the UV lines only?
No, that shouldn’t be an issue. At least it wouldn’t be if things work out.
The only feature I will not attempt to touch is having it work with live subdivided surfaces. The workaround would be the same one suggested with the geometry constraint plug-on, and that is to apply the “mesh subdivide with center” operator to the mesh, and then use the resulting object as the constraining mesh. I hope that would be a reasonable compromise.
just realized—I never tried this, but there could be a chance things with subdivs might work out transparently when you use CGeometryAccessor with the current subdiv level as the in_subdLevel parameter.
(This is assuming it works as advertised and I didn’t completeley misunderstand the sdk docs)
The next problem then would be to find a good data structure for the uv->triangles lookup
I haven’t tried it myself, but that’s not the problem really. The issue is that I’m relying heavily on the Point Locator API, which doesn’t have any provisions for querying for point locators on the subdivided mesh. At least none that I can find.
Regarding that, I think I’m on to something:
The video above shows a very naive implementation of a scripted operator that constraints an object to a point on the surface of a polygonal mesh determined by the U and V coordinates on the mesh’s texture map.
It’s working well I think. But it will not follow the surface if the constraining geometry is deformed. And the data structures were pre-generated using an external python script.
I’ll try to finish it as time permits, but I doubt I’ll have any time to spare for the next week or so due to some crunch time coming at work.
That said, I think it looks very promising so far. Fingers crossed
I haven’t read the whole thread so far but it’s easy task with the Object To Cluster constrain.
Just select the object to constrain, then the object with component to constrain, and select the component (all is suggested in the mouse status line)
Then adjust the Tangency and the normal. That’s all. It’s included at leaste since v 4.2 (when I started with softimage)
Object to cluster will only take a component or the average of several as in input.
Constraining to a mesh and offering access to barycentric interpolation on face is a whole different deal and isn’t possible out of the box (outside of ICE that is, which doesn’t offer supported kine access yet).
So what happens if the input U/V coordinate falls on an empty section? Maya’s rivet setup goes nuts and it defaults to an odd location. Same if you cross over an empty section back to a section that has UVs laid out in it.
Just wanted to see what your thoughts were on this and whether the script take this into account.
Eric T.
That’s a valid concern. Unfortunately, I don’t have a concrete answer at this stage. Aside from the small test posted earlier in this thread, all I have is an idea that seems to make sense to me, and it should work reasonably well in the scenario you’ve mentioned.
Thank you. Any chance to get out of the echo chamber and bounce ideas around is highly appreciated.
I should mention that’s it’s no longer a script I’m writing this one as a compiled plug-in, and it’s taking me a while to get back on the C++ saddle. As I mentioned before, things are a little busy at work these days. But I’m still able to put an hour or so of work into this every day. If anyone feels like geeking out, you can view the source code at this repository hosted on bitbucket.org.