Pilot lights

It’s been too long since my last post. The reason for that is simple… I’ve been very busy on the paid work front and some other stuff. One of the things I’ve been working on recently is a new short film currently in post-production from fxPHD. In this project, I’m working on the pilot light of a flame thrower. So it was time to pull out Houdini’s PyroFX . And that’s a lot of fun!

The PyroFX tools are not particle based but volumetric. I started out with the Flame tool from the PyroFX shelf. After a lot of tweaking I got it to produce something that looked more or less like a small gass flame. The simulation of this flame (as used in one of my shots) looks like this:

pilotlight_sim

There are many layers of data that are processed in a typical pyro setup, called ‘fields’. In this case, I’ve visualized the ‘heat’ field as I used that as the base field for the pyro shader in my shots. This visualisation is also great reference for comping the element into the background plate, as it shows nicely now the flame and the nozzle overlap. It is possible however to visualize all the other fields as well and/or use them in your shaders or for whatever you’d want to use them. Lots of flexibility here. The simple geometry of the flame thrower was part of the match moved scene files I got for setting up the pyro for each of my shots.

On of the great features (definitely one of my favorites) of the pyro tools in Houdini is the fact that you can ‘resize’ and animate the volume container in which the simulations run. This means that instead having to create a container that is large enough to contain the entire space through which your pyro travels (in the case of a flame thrower carried by a walking person, quite a big space), you can have a container that is just big enough to contain the ‘local’ space required for the flame. Once you animate the container (using the ‘resize fluid’ DOP) the simulation behaves as though it occupies the entire space that is covered by the moving container.

I kind of think this like the container is some kind of ‘region of interest’ like you can use in compositors to limit the render time, only in this case the ROI is a volume. The sim itself operates in world space with the calculations limited to the ROI defined by the animated container.

This saves a TON of simulation time as it dramatically reduces the amount of voxels in the volume container that need to be taken into account for each calculation.

The following movie file shows a simple comp with the rendered pyro element integrated into the background plate. I cropped the frame to only show the nozzle of the flamer and my pyro sim, as the film is not released and I wouldn’t want to show too much of it.

pilotlight_crop

This is not by any means a final or approved comp but it shows roughly how the pyro element will end up in the complete shot.

Anyway, these are some fun shots to work on. I’ll post more information on the short film when its released.

Cheers,

Erik