Houdini

Cloudscapes via Volume Vops

It’s an understatement to say that Houdini volumes have a lot of depth, there are just so many possibilities and fun things to explore. After making a few requisite pyroclastic clouds I decided to see what can be done without DOPs. In other words, what kinds of effects can you get without simulation or just converting input geometry? Here’s the first part of an answer – you can use VOPs to create animated volumes and cloudscapes that are surprisingly fast. In these I first filled a volume with a sin wave and then introduced alligator and perlin noises at different frequencies following the sinusoidal surface.

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