#fromthedocs

Motion is evaluated at sub-frame intervals. If you use expressions to animate objects or deformations, you should use $T (floating point time) or $FF (fractional frame number) in the expressions instead of $F (integer frame number). Expressions that use $F will not show motion blur properly (since the expression will give the same result at every sub-frame).

Mantra’s Delayed load shader replaces the geometry of whatever object it’s assigned to with geometry loaded from disk at render time. This is very useful when you want to work with light-weight, low-poly geometry for speed in the viewport, but need heavy, high detail geometry at render time.

Warning: Never animate an object containing Object Merges. Parent the object to a Null and animate the Null.

On Mac OS X and Linux, Houdini uses the system’s Python. On Windows, it uses the version of Python installed with Houdini.

On Linux, Houdini does not look at $PATH when trying to search and load the Python library. Instead it searches all the paths in $LD_LIBRARY_PATH, then /lib and then /usr/lib. If it can’t find a suitable Python library in the system, then it defaults to the one in $HFS. If your Python library is not in a standard location, you should add its directory path to $LD_LIBRARY_PATH.

If you want the object to simply shatter on impact, a quick solution is to use the Make Breakable tool on the Rigid Bodies tab of the shelf. It uses the same voronoi fracture method as the Shatter tool, but gives you less artistic control. It is better to use Shatter for foreground shots and Make Breakable for objects in the background.

A point group can be ordered or unordered. Unordered groups store their points in creation order; ordered groups store points in selection order.

When you select points in the viewer pane, a single click performs an ordered selection, while a marquee box generates an unordered group.

When you merge two or more branches in a geometry network, if a detail attribute with the same name exists in multiple branches, Houdini uses the value in the first branch. If the attribute is a string array, Houdini merges the arrays.