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RBD Sim Render Geo output possible?


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Hi Houdini Magicians,


I have a question about the RBD Packed Primitive Object. In the 'Display Geometry' option of the RBD Packed Primitive Object is a choice between the actual simulation geometry and a Render Geometry with a SOP path.

When I output the RBD object out of my DOP network it uses the Simulation Geometry by default.

Is there any way to output what I see inside the DOP when choosing Render Geometry?

Replacing the Simulation Geometry with the high res render geometry gives me a lot of trouble when I am using deforming active objects but inside the DOP the render geometry works perfectly, so it would be the easiest to just get that data out of there if possible?


Thanks for any information regarding this. Being fairly new to Houdini, still, I can't imagine that there is no way to export any data out of a DOP that can be seen when inside a DOP.

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You may want to leave the Display Geometry set to Simulation and explore the import options on the DOP Import node instead. From there you can decide how you want to fetch the data from the AutoDOPNetwork. You may not have noticed, but there is no Render tab for the AutoDOPNetwork. So it is common to place a DOP Import inside a geometry node so you can apply a shader. Try changing the Import Style, packed geometry may run faster in the viewport. You also get an Object Mask field so you can throw away simulation junk you may not want to render, like the groundplane, for instance. This field supports asterisk for wildcard and carrot for exclusion of named nodes inside the AutoDOPNetwork. (* ^groundplane1 means import all objects except the groundplane.)


Edited by Atom
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Thank you, Atom, for taking the time to explain this. I am aware of the functionality of the DOPImport node but there is no way to fetch the 'Render' Geo specified in the RBD Packed primitive. Unfortunately neither 'Transform Pieces' works correctly or in the DOPImport 'Transform Input Geometry' does not work either. The issue is that the fractured object is animated (deforming) and I haven't found a way to truly override the transformations. It is always just adding transformations on top of the animation.

If there is a way to literally override absolute the transformations in world space of packed geometry with the transformation of other packed geometry with the same name attribute, that would be swell.


I might have to explain an example:  At the beginning is an animated and fractured objects (packed primitives). For better collisions, I have a "collision proxy" version of those packed primitives, made up of sphere primitives. Works great in the Bullet simulation. But for rendering, I need the simulated proxy to be replaced with the render geo again. Again, all the packed stuff is in sync, pivots, name attribute and so on.

But no matter if I use transform pieces sop or try to use DOPImport, Houdini gets confused with the already moving geo. Freezing the geo at the 1st frame does not work either. Technically it would need to use the frozen position for each piece when changing from deforming to active rigid body. Maybe I can store that frozen transformation at activation time some how and the re-apply it later.

If I don't use my special collision proxy geo and just import the geometry out of the DOP it totally works well. No problems! Except that you cannot have fast concave collision pieces. My fractured geometry is definitely not convex. Therefore it is not working well with Convex Hull mode. My sphere based proxies work super well.

I probably should prepare an example file. I am sure there is a solution but I doubt it is easy and straight forward like just using DOPImport.

Again, thanks a lot!!!






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