As part of the pipeline I’m currently writing for Timber, I’ve been working on an input/output system that can pass data back and forth between Maya and Houdini. The goal is to have a Maya artist send an Alembic scene to Houdini, process the scene in Houdini, then send the Read more…
I realize this effect was done years and years ago by smarter people than me (JT Nimoy, Adam Swaab, among others) but I’m a big nerd for procedural art and wanted to see how I could create the Quorra Heart effect described on Nimoy’s blog here. The effect itself isn’t Read more…
I’m working on a production right now that involves sending absolutely enormous animated meshes (6.5 million polygons on average with a changing point count every frame) out of Houdini and into Maya for rendering. Normally it would be best to just render everything directly out of Houdini, but sometimes you don’t have as many Houdini licenses (or artists) as you’d like so you have to make do with what you have.
If the mesh were smaller, or at least not animated, I’d consider using the Alembic format since V-Ray can render it directly as a VRayProxy, but for a mesh this dense animating over a long sequence, the file sizes would be impossibly huge since Alembics can’t be output as sequences. Trying to load an 0.5 TB Alembic over a small file server between 20 machines trying to render the sequence and you can see why Alembic might not be ideal for this kind of situation.
Hit the jump below to see the solution.
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Side FX added a new Cloud FX toolkit a version or two ago, and I recently had a chance to mess around with it. Their Cloud Rig shelf tool is pretty great out of the box… pick a shape, turn it into a cloud, done. The Cloud Noise and Cloud Light SOPs that are built into the rig setup can get some pretty good results, but it’s not exactly what I wanted… I was looking for a solution that would be a little less dependent on the volume container resolution, and more based on textures instead. It’s not necessarily the greatest solution for swirling, dynamic simulations, but for more-or-less static clouds, it gets resolution-independent nice results that are quick to generate. Maya’s fluid shader supports textures by default, but the Cloud Shader that Houdini uses doesn’t have much in the way of textural control, so I had to make some customizations, and that’s what this post is about. Check the link below to keep reading…
One of the bigger challenges with rendering liquids is that it can be difficult to get good UVs on them for texturing. Getting a displacement map on a liquid sim can make all the difference when you need some added detail without grinding out a multimillion-particle simulation. Unfortunately, liquid simulations have the annoying habit of stretching your projected UVs out after just a few seconds of movement, especially in more turbulent flows.
In Houdini smoke and pyro simulations, there’s an option to create a “dual rest field” that acts as an anchor point for texturing so that textures can be somewhat accurately applied to the fluid and they will advect through the velocity field. The trick with dual rest fields is that they will regenerate every N seconds, offset from each other by N/2 seconds. A couple of detail parameters called “rest_ratio” and “rest2_ratio” are created, which are basically just sine waves at opposite phases to each other, used as blending weights between each rest field. When it’s time for the first rest field to regenerate, its blend weight is at zero while the rest2 field is at full strength, and vice versa.
It’s great that these are built into the smoke and pyro solvers, but of course nothing in Houdini can be that easy, so for FLIP simulations we’ll have to do this manually. Rather than dig into the FLIP solver and deal with microsolvers and fields, I’ll do this using SOPs and SOP Solvers in order to simplify things and avoid as many DOPs nightmares as possible.
Here’s the basic approach: Create two point-based UV projections from the most convenient angle (XZ-axis in my case) and call them uv1 and uv2. As point attributes, they’ll automatically be advected through the FLIP solver. Then reproject each UV map at staggered intervals, so that uv2 always reprojects halfway between uv1 reprojections. We’ll also create a detail attribute to act as the rest_ratio which will always be 0 when uv1 is reprojecting, and 1 when uv2 is reprojecting. It all sounds more complicated than it really is. Here goes…
I ran into a problem recently where I was trying to make some nice-looking embers in houdini, complete with nice motion-blurred trails. Typically with a particle system you use the velocity attribute to handle motion blur, but geometry velocity blur is always linear, so your motion trails will always be perfectly straight even if you have nice squiggly motions with your embers.
Deformation motion blur looks great, but in most simulations particles are being born and dying all the time, and deformation motion blur doesn’t work with a changing point count.
The solution is to force a constant point count. This can be problematic when your particles need to have a lifespan, so there are a few little tricks you’re going to have to pull in order to make this work…
I just wanted to post a little bit about the Creep POP in Houdini because I’ve had such a hell of a time getting it to do anything useful. I was trying to create the effect of raindrops sliding down glass. In Maya, this is a pretty simple thing- enable Read more…
My latest gigantic Houdini project is finally live! I was the Technical Director for this one, which also means Houdini tube effects, lighting, shading, rendering, etc. Thanks to my fellow Houdini artist, Alvaro Segura, for handling the inky effects, as well as for helping me to refine the tube generator Read more…
Just wanted to document a dumb little problem I was having. My compositors need cameras in .FBX format, and I had a camera that had a Look At object (an aim vector) which wasn’t being considered in the export. I tried parenting a duplicate of the first camera to the Read more…
I’ve been very, very busy, which is a lame excuse for the lack of posting new things, but there you have it.
Much of my work time recently has been dedicated to building inky, nebula-like effects in Houdini. Generally speaking, when you’re trying to make that whole ink-in-water effect, you dust off your copy of 3DS Max, do a quick fluid simulation, advect a bunch of particles through it, and then cache out a bazillion partitions of your simulation with different random seeds, then render in Krakatoa. Well, I have none of those things, and I needed greater control over the simulation than what can typically be achieved in Fume/Krakatoa, so I tried to do it in Houdini. I definitely have a lot of respect for the Krakatoa renderer after a week spent on this effect. This stuff is hard! Hit the jump to see exactly how I went about this…