SETTING UP ANIMATED GEOMETRY TO GUIDE SIMULATION
1
After fracturing the object of choice, create a bound SOP to ensure the entire fractured object is encompassed within the animated geometry’s interior. If the fractured object is concave, use multiple transform SOPS to conform the bounds to the edges of the fractured geometry to reduce any area of the bound that does not encompass the fractured geometry.
2
The RBD Bullet Solver works best when the animated geometry is divided into individual segments based on connectivity. This allows the fractured geometry within each segment to be animated specifically to that segment. To create the segments out of the bounded or ‘animated geometry’, drop down a grid for the x, y, and z axis. Then use a copy SOP under each grid to copy the grid in the direction of each axis. Merge the copy SOPS and drop down a mountain to create some variation between the segments. Under the transform node(s), drop down a Boolean connected to the mountain to create the segments.
3
To remove any small segments that may cause problems later in the guided simulation, measure the volume of each segment and delete based on a small volume threshold.
Under the Boolean(s), drop down a connectivity SOP to isolate each segment, then a measure SOP with the Accumulate parameter set to Per Piece, with the Piece Attribute set to class to run the volume operation over every connected segment. Next, drop down a blast with the expression ‘@volume<0.1’ to delete the segments with small volumes. Depending on the scale of the animated geometry, the volume threshold will vary.
4
The animating of the animated geometry is contingent on the project, and is up to the artist to determine the overall simulation timing and look. In this project, the animated geometry bends and twists into itself, guiding the fractured building simulation to turn inwards and destroy itself. A bend SOP is placed under each blast, with the bend and twist parameters animated. Finally, an assemble SOP is placed under each bend SOP with a unique ‘Output Prefix’ name, the Create Packed Geometry toggle is checked on, then merged into a merge SOP. This ensures each segment has a different name when entering the simulation.