# Houdini

## Unreal Screenshot

Just messing around, this time taking particles from Houdini into Unreal.

## 10 Free Vector Fields

This is a collection of 10 vector fields in .fga format.

## Volume Waves

Example of a volume field populated solely by VOPS. (.hipnc)

## Websling

A webbing rig, stretches nicely between two controls, lots of user control. Could go a lot further with this of course but I wanted a fast exploration utilizing and testing some of the generic asset’s I’ve made so I probably will leave it here until I feel like doing an animation with it.

## Getting a camera position in Vex, using optransform and cracktransform

In an earlier post I used a very unwieldy approach to get the position of a null in vex. Since then I have used a method where an object_merge SOP is set to transform “into this object” and then a point function can easily read the first point in the null to arrive at a center position. The problem with this is that you are reading the icon geometry for the object and in the case of a null this is ok, but the camera icon has each point offset from it’s origin.

Enter optransform and cracktransform. The optransform function will let you set a path to the camera (or whatever else you may want to use) and then populates a matrix with the target’s transforms. You can then extract out the position as a vector using the cracktransform function… this function if pretty powerful and at first confusing but essentially it has a switch which let’s you specify the portion of the matrix you need.

In the example above I used these functions to get the camera position and then used that position to compute a direction in “camera space’ to allow a ray SOP to project scattered points onto an object as a camera projection. Sounds complex, but it’s not. Here’s the wrangle which uses optransform and cracktransform to get the camera position:

```vector @cdir;
vector @raydir;
matrix camMatrix = optransform(chs("camera"));
//get a matrix with the camera's transforms.
@cdir = cracktransform(0, 0, 0, {0,0,0}, camMatrix);
//extract out the camera position as a vector
@raydir = normalize(@P-@cdir);
//get a vector to project pointo from camera```