When doing DOPs simulations with an RBD fractured object, what is the general consensus on how to disguise the cracks in prefractured geometry before the geometry is meant to break apart? I have been told that adding a fuse SOP to the object merge which merges your simulated geometry into SOPs gives the illusion that your geometry isn't cracked. While this seems to work in some situations, in many it does not.

For example I have prefractured a grid into a number of triangles and then dropped the grid on the floor in DOPs. It smashes apart nicely. Now I want to render it out I slapped a VEX Glass on it and set up some GI. The trouble is I can see all the triangles as the glass sheet is falling, even when I try adding a fuse SOP. Is there any other methods of disguising these prefractured elements?

first thing that come to my mind is the simple visibility trick. use non-fractured model till frame 12 and in frame 13 swap it with with a fractured one… it is not an elegant solution… but it's a kind of….

I thought that first but the glass is at an angle so one end hits the floor first……

Heya Dean,

A trick I sometimes find usefull, is to calculate the normals on the solid geometry, and store then in an attirbute (Nconsolidated) – then “shatter” the geometry using some method, and simply transfer the Nconsolidated attribute back to the shattered normals.

This will render the object as if it weren't shattered (assuming of course that you tranfer Nconsolidated to N).. and now all you have to do is figure out how to blend between the fractured normals, and the solid ones… based on time, or possibly based on the distance of the centroids of each piece to each other relative to the whole “unexploded” mesh.

Hope this helps…

Cheers,

G

Heya Dean,

A trick I sometimes find usefull, is to calculate the normals on the solid geometry, and store then in an attirbute (Nconsolidated) – then “shatter” the geometry using some method, and simply transfer the Nconsolidated attribute back to the shattered normals.

This will render the object as if it weren't shattered (assuming of course that you tranfer Nconsolidated to N).. and now all you have to do is figure out how to blend between the fractured normals, and the solid ones… based on time, or possibly based on the distance of the centroids of each piece to each other relative to the whole “unexploded” mesh.

Hope this helps…

Cheers,

G

Hey keyframe,

I'm following what you're saying…but I'm afraid I lack the specific Houdini knowledge to carry it out. How do I calculate the normals and then store them in an attribute?

Thanks for your suggestion..

Hey Dean,
Facet SOP computes them, Attribute Transfer copies them over…

Cheers,

Peter B

Hmmm…time to sound really dense….. ops:

I've put a facet SOP down and checked ‘pre-compute normals’. How do I then specify in the AttribTransfer that I want to transfer the normals over? I checked ‘Points’ in the Attributes tab and then selected N in the list but nothing changes….

You may have the input objects connected in the wrong order - the first input is the one you want to transfer to, not from, which always throws me.

Here's an example. Turn on display of point normals in the viewport, and make it wireframe, to see what is happening as you display the various nodes.

Thanks a lot for that, i'll take a look……