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In this series of software reviews, Allan McKay has been comparing industry-proven fluid
applicationscurrently in use to create smoke, fire, explosions and related effects for film,
TV and games. Previously, he looked at Maya’s built-in Fluids Solver and 3D Studio
Max’s Fume FX. But this time he’ll consider Houdini 10’s new Fluid Solver ‘Pyro FX’,
which is the latest fluid option to be released, comparing it to the older Maya Fluids and
Fume FX Plugin.


click for larger images
ide Effects software have put a lot of effort into this product, building a robust tool with some excellent features, but still fairly easy to access and utilise in production. One advantage Pyro FX has is Houdini itself. Houdini has been designed with control and accessibility in mind, and pretty much every node and attribute is exposed and able to communicate with everything else. As a consequence, these fluids are also node based, so you're able to get a lot more control with your fluids than when using some other packages by building complex node workflows.

Using Presets
Because of this, artists and technical directors will be able to pipe shaders or geometry through that can test for certain key information and communicate back and forth during the sim, or expose a lot of the information output from the sim into a shader or surface geometry. A lot of this capability is achievable both in Fume FX and Maya Fluids, but not really as intuitively as Houdini is able to do.
Houdini 10 comes with an assortment of preset fluid FX to get started with. This is great while learning the new features, as you can see pre-made examples to help with deconstructing the effects, but they are also useful as an example of how to fast track your production techniques. If you are creating lots of fire and smoke, for example, by building presets for these it is easy to literally drag and drop into scenes and modify the key values. Or you can pass them on to junior or mid-level artists to apply to their shots, without their needing much previous knowledge of how the effects were constructed. All they really need to know is which values adjust wind/emitter source or similar information. As with anything in Houdini, all of these details can be black-boxed to make the process more straightforward.

Up-res Your Sims
In terms of simulation speed, Houdini 10 is fast - not as fast as Fume FX perhaps but definitely faster than Maya. However its power comes into play especially when using the up-res feature. With this, you're able to get your 100x100x100 simulation, for example, and up-res the container to a higher resolution like 300x300x300.
With previous simulations, you may have noticed that when simulating your 50x sim at 200x, the motion changes dramatically as more information and volume changes the results. By up-resing your sims, they will keep the exact same motion but at a much higher resolution and more importantly, you're able to get much more detail without necessarily having to re-simulate. Calculations are involved but it is definitely faster and is network distributable. If you’re doing your sims locally, for example, and find something that you think is worthwhile, send it to the farm to reconstruct at a much higher resolution.

Shaders
Houdini's shaders are reasonably powerful and accessible. The viewport controls are a genuine asset, and mean that you can display a shaded preview in your viewport. This is great for visualising with everything else in your shot, such as characters and other objects it may interact with. The best part is that it is completely colour coded to be dissected into sources of fuel, temperature, density, divergence, burn, heat, velocity, collision, source and so on. You can really see what your fluids are thinking as they sim, and afterwards. Fume FX has all of this, too, but the main difference is how fast Houdini is able to draw this information in the viewport.
Pyro's Shader Operator looks very good. As previously mentioned, the fire is effective but not great, although it does have nice scattering features much like Fume has, which makes for good interaction between fire and smoke or for cloud effects. As with all of the fluids packages, you're able to pipe out vector information to drive particles or dynamic sims, and emit from particles, both of which are necessary features for production. The shader editor gives an amazing amount of control by allowing shader to be driven based on heat, fuel or pretty much anything else, but then piped through expressions or multiplied by anything else in the scene. Additional fields allow for further control. The shader works also well with Houdini 10's new improved renderer.

Node-based Advantage

It’s especially useful to compare Pyro FX to Fume FX because, in my experience, Fume FX is really the reining champion of commercial fluid solutions available now. Fume, I believe, has slightly better fire results over Pyro and slightly faster sim times. Nevertheless, Houdini stands out with its flexibility and as the first solver to take advantage of its node based environment, whereas its competitors are all linear by nature, requiring major scripting to get any real control from the fluids.
While it is the latest fluid solution to hit the markets, it's obviously had time to mature. Maya Fluids is some six years old and Fume FX is just a bit over four, although major enhancements for both max and Maya may emerge in the near future for fluids. Meanwhile, a new batch of fluids solutions could hit the market in the next year or so boasting lots of new features putting Pyro FX to the test. Houdini is a very robust system, but still labeled as a specialist tool.

Integration

Since releasing Houdini 9, Side Effects seems to have pushed to make Houdini a bit more mainstream and easier to follow, hoping to gain a wider following. Houdini 10 definitely has made many improvements on an already strong system. It is able to handle both water and gas based fluids now. Taking advantage of its particles, shaders and dynamics, as well as procedural node based system and python support for scripting, it is definitely starting to stand out as a solid production tool to handle most areas of visual effects.
All in all, Houdini 10 is a strong fluid solver that should cover most studios’ fire and smoke needs. Where it stands out is in its node based workflow and its up-resing technology. Completely integrated into Houdini, rather than a plugin, it can make further use of its integration with other modules of Houdini. It's fast to work with, fairly fast to simulate and definitely worth building into your studio pipeline.

References & Resources:
Houdini -www.SideFX.comHighEnd3D -www.highend3d.com

Review by: Allan McKay,This email address is being protected from spambots. You need JavaScript enabled to view it.
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