Multi threading mesh boolean

Hi all,

Ive been trying to create a python script that takes a set of meshes and create a boolean difference with another input mesh. Like puncturing holes in a mesh surfaces.

I want to see if multi threading speeds up the process, because if you go above 500 'holes' it gets super slow (like 4 minutes, and 10 minutes for 600). I checked out Steve's blog post: http://python.rhino3d.com/entries/607-Multithreaded-Python and created my own version but i keep on having the error: 'Aggregate exception: various errors are produced'.

attached is the grasshopper file (with the python component)

Thanks in advance!

gh def: meshboolean.ghx

Replies to This Discussion

Permalink Reply by David Rutten on June 26, 2012 at 5:06pm

Permalink Reply by David Rutten on June 26, 2012 at 5:17pm

Are you trying to punch holes into a single mesh from multiple threads? If so, forget about it. It'll never work.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Arie-Willem de Jongh on June 26, 2012 at 5:28pm

Haha David :)

I'm afraid that is the case... I use a for loop where I use my initial mesh and iterate one by one trough my boolean meshes re-using the mesh that comes out as the input,

something like:

tMesh = mesh #big surface where the hole are going to be punctured in

meshes #the boolean meshes that are sticking trough the mesh

for i in meshes:

---tMesh = rs.meshBooleanDifference(tMesh,i,True)

I was hoping i could spread the actions in the for loop over multiple threads, check out the link I posted, I believe Steve did something similar, only with a plane/brep intersection- for loop.

Steve said in the post and I qoute :'This set of classes and functions makes it relatively easy to write things like parallel for loops in which every iteration of the loop may be processed on different threads'. The 'relatively easy' sounded quite appealing haha, but i guess it is more complex.

Thanks!

Permalink Reply by David Rutten on June 27, 2012 at 1:36am

Plane|Brep intersection is fine because neither of those should affect the state of the data operated on*. However, you're modifying a mesh simultaneously from multiple threads, there's bound to be conflicts. The only way to solve this is to create a lock on the mesh object during one boolean operation, which sort of ruins the whole idea of multi-threading.

If you were punching holes in multiple meshes, you could solve one per thread, but a single mesh... nah. Just nah.

David Rutten

david@mcneel.com

Poprad, Slovakia

* this is actually not really true. It's possible that there are caches and trees that will be constructed the first time you call a Brep intersection functions, but this only needs to happen once so a thread lock during cache construction is not that big a sacrifice.

Permalink Reply by Arie-Willem de Jongh on June 27, 2012 at 8:28am

Thanks David for the clear explanation! I guess back to the drawing board...

Permalink Reply by Vicente Soler on June 27, 2012 at 12:55pm

To speed things up you can either subdivide the surface or mesh into smaller pieces before trimming the holes or you could create a bitmap image through grasshopper to use as a transparency texture for rendering.

Permalink Reply by Arie-Willem de Jongh on June 27, 2012 at 1:36pm

The latter Im using now for the renders. The thing is that the guys that render are kind of 'lazy' , they asked me if it would be possible to create the holes (so they wouldnt have to make the textures for rendering). But I think given the time the texture option is the one we're going for.

Maybe later ill try to subdivide the mesh first into smaller parts so i can spread those over multiple threads. Lets see.

Permalink Reply by Vicente Soler on June 27, 2012 at 2:16pm

Even if you don't use multiple threads, it will still be much faster.

Some time ago I made a definition that given a set of surfaces for each surface it created a transparency texture, a material, assigned the transparency texture to the material and assigned the material to the surface, all within the definition.

I rendered it inside Rhino. If you are rendering in another software i think there are some file formats that can export materials but i haven't tested it.

Permalink Reply by Arie-Willem de Jongh on June 27, 2012 at 3:36pm

Ah that sounds pretty cool! They use 3Dmax + vray, I think the .fbx (motionbuilder) exports the material, so that might be an option. But we're out of time to experiment unfortunatley. They're already almost finished doing the textures. Thanks!

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