## VEX: Spinning Particles

The titles should really be how to rotate the orient attribute but spinning particles is more catchy. Rotation can be a tricky beast and when it comes to particles there are a bunch of ways to control their direction, and when you are stacking multiple rotations things can become a little hairy! I suggest using quaternions to control direction because the qmultiply function makes it very simple to modify the current orient.

## Groups to Attribute with VEX

Today at work I was loading some really heavy geometry into Houdini that needed FX added to it. Its came in from Maya with thousands of primitive groups for different numbered parts of the geometry. If you tried it before you will know that unpacking heavy geometry with a lot of groups is any easy way to fill up your ram. In this cache filling 64GB and the cracking Houdini after filling the swap as well.

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## Quick Tip: Rounding To Decimals

This is going to scaling sets of numbers so if you are bored already now is a good time to go and browse something else. A friend at work asked how do I round a set of values to the nearest value with an increment of 0.5. Why would you want that you might ask? Its useful for scaling data by specific increments like for driving values along a curve.u value to create stepped noise without using a ramp. Here is how you do it.

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## Quick Tip: The Handy Falloff Sop

Combining the falloff sop with a few groups is a great way to control attributes by distance without having to jump into VEX and VOPs. A lot of sop nodes output groups along with the operations they do so I figure you might as well use them when you have the chance. Here are a few examples of the falloff sop in action.

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## Quick Tip: Cleaning Node Spare Parameters

This one is motivated by a question someone asked on the Redshift forum. The Question was when updating Redshift, how do you get the new features added to object parameters on old nodes from old hip files? Because Add OBJ Parameters in the Redshift menu does not work if you have Redshift parameters applied to the object already and even if you delete them using the Edit Parameter Interface choosing Add OBJ Parameters in the Redshift menu does not add new parameter menus.

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## Multiple Flipbook Sessions

Ever flipbook to Mplay and overwrite your previous flipbook? Or Have a flipbook from one Houdini session overwrite the frames from a different Houdini session to the same Mplay and think to your self Dammit?! I do it all the time and find it mildly frustrating but not enough to do anything about it. Continue reading “Multiple Flipbook Sessions”

## Quick Tip Code: Extracting a Vector From a Quaternion

Usually I am doing the opposite operation building an orient attribute from a set of vectors.