adding noise/field effects in certain areas

Lifted from the Houdini help page.. Useful for localised noise/breakup

You can attach DOP nodes that modify velocity fields, such as Gas Turbulence, to the fourth ("Advection") input of the Pyro solver node. Most field-modifying nodes have some way to scale the effect by a mask field.

Create a geometry object in the shape of the area you want to affect.

Convert geometry to a fog volume - use an isooffset

In the DOP network, add a SOP Scalar Field node after the Pyro object.

• Turn on Use SOP Dimensions.
• Set the SOP path to the path of the fog volume object (for example /obj/mask_object). Make sure Use Object Transform is on.
• Set the Data Name to something indicating the purpose of this field, for example NoiseMask.

This attaches the fog volume as field data on the Pyro object with the given name.

Create a Gas Turbulence node and connect it to the fourth ("Advection") input of the Pyro solver.

• On the Bindings tab, set the Density Field to the name of the mask data, for example NoiseMask. The effect of the node is multiplied by the value of this field.
• Use the controls on the Turbulence Settings tab to control the amount of turbulence added.

camera projection with houdini

Houdini camera projection is as simple as creating a "UV TEXTURE" node and plugging it into the geo you're projecting onto.
In this node, select "Perspective from Camera", from the Texture Type dropdown menu.
You could name the UV Attribute something other than the default of "uv" if you are creating some alternate uv sets.
In the Camera dialog box, specify the camera node. Eg. /obj/cam1 & usually the attribute class for the uv's will be set to vertex.

Now, whatever material you apply to it will use these uv's. (or maybe a different set if you specify within the shader network!) eg. uv2.

size of array, VEX snippet

i@size=len(i[]@nameOfArray);

the [] is actually [   ].

activating particles

to have particles come alive, mid sim (or indeed, to have them stop mid sim) you just need to trigger the "stopped" attribute in your pop network.

blurring vdbs

float dist = xyzdist(1,@P);

float distremap = fit(dist,ch("near"),ch("far"),0,1);

f@density *= distremap;


This gives a vdb a falloff based on how close it is to the original object's surface.
Stick the VDB into a volume visualisation and then plug that into input 0
Put the original geo into input 2.

Now you can "blur"

group centroids

group centre/centroid - intstead of blasting out groups and using $CEX etc, you can just use $GCX, $GCY, $GCZ in your transform pivots.

Selection expand

To expand - any - selection like in Maya... do your selecting then press SHIFT G (to grow) or SHIFT S (to shrink)