Houdini: Setup Fractured Glass The Right Way For Seamless Rendering

You have a fractured window glass pane, or a glass ball for RBD simulation and rendering, but the inside faces of the fractured pieces show in the render even before the fractured simulation plays. The demo below shows the problem on the left and the fix on the right

The obvious solution is to resort to "tricks" to hide the pieces but Houdini since 18 introduced nodes to handle that problem; two nodes actually.

Let's go!

• A basic geometry fractured with the glass preset of the "RBD MaterialFracture" node. = The first important step is to drop an "RBD ConnectedFaces" node
• The next step is to do whatever you wish to do with the fractured object. ie. the sim or animation or whatever it is you want to do.

• The last step is to drop an "RBD Disconnected Faces" node and choosing Delete Connected Mode

That is it !! Simple! huh? What happens is that, all the inside faces of the "unsimmed" faces are deleted while the simed faces are not. This creates a hollow geometry of a sort and only fills the areas that get disturbed. In the wireframe below, the first box is a clipped version of the fracture box. It is clear that the box is hollow at that point until any area gets hits and has to fall apart (last image).

Have fun!