Houdini

Vector Fields 1

Writing custom vector fields is pretty easy in VOPs. You can leverage the multiple noise functions Houdini offers, easily create vortices and whirling clouds, and with just a bit more effort bring in curves and use them as paths which the field can orbit around or follow along. Whip up an additive shader and you can get very nice results… or export the fields to use in Unreal or some other game engine. I plan on eventually offering a number of free static vector fields here on the site for game effects artists, but for now here are some basic test renders, cheers.

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

Vex setpointgroup snippet

Since I was making circuit looking stuff I tried a different approach above, and in doing so had to explore setting random points into a group via Vex. Enter the setpointgroup function, very handy indeed. This snippet creates a group of random points based on a threshold, and is useful enough to take note of:

if ( rand(@ptnum+chi("seed")) < ch('threshold') ) 
{
setpointgroup(0, chs("Group"), @ptnum, 1, "set");
}

Circuit POP

This was fun and quick to do by restricting the direction particles could move to 45 degree increments and keeping them flat on the ground plane. Eventually I’ll be posting .hip files with these posts, once I get this blog’s back end a bit more up to date.

Circuit Pops