creating anime style smoke

There has been a great deal of interest in recent months in toon shading techniques for 3D animation. I have been doing a great deal of anime-style rendering lately, but I have had trouble re-creating that awesome smoke effect that so many cel-based anime movies enjoy. However, I have found a few secrets on how to achieve that effect, and now I will pass that information on to you.

The problem is this: in anime-style shading, there are generally distinct bands of color around an object with no shading between them. This is a very difficult effect to achieve with ordinary particles in Softimage because the particles always either have a gradient-shaded or constant color.

However, objects in Softimage can be shaded pretty much any way you like, including anime-style. Enter "Go with the Flow". It allows you to combine the best part of particle animation (the flowing, smoky motion) and the best part of Softimage rendering (the anime-style shading) and combine them in one effect.

In this tutorial, we'll create anime smoke using the Go with the Flow plugin and meta-clay.

about go with the flow
Go with the Flow uses particle's BPF output option. BPF stands for Binary Particle File. It creates a single file containing all the information from your particle scene. Up until recently, it was basically a useless function on NT systems because it was unsupported (although IRIX has had Go with the Flow for some time now). Recently, an NT version of the software has become available.

Go with the Flow is available on Softimage's web site at www.softimage.com. You'll find the NT version in the Technique area under Softimage 3.7SP1 plugins, and the IRIX version can be found in the Technique section or in the support section. NT users will also need Particle QFE. Look for it in the Particle area of the technique section. To install it, just follow the instructions provided.

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the particle system
Go to Source>New to get a default emitter. Set the rate to 20 and the spread to 10. This will give you a nice little particle stream.

Now we'll add some wind to the system to give it a little more interest. Go to the Particle card and set the friction to 1. Then go to the global wind card (F10) and set the strength to 1. You can play around with the wind icon (on the left side of the screen) to interactively adjust the azimuth and inclination so the wind is blowing across the camera plane. Somewhere around 0 azimuth and 90 inclination will work best.

That's about it for setting up the particle system. Now we have to render out the BPF to bring into Softimage. Go to the File card and click Render. In the Output Type section of the Render Setup window (the first set of options at the top left) select the Binary Particle File option. Make the sequence 1 through 100 with a step of 1.Choose your database in the output section and name the file smoke. Click Render Sequence.

the meta-clay
Go to Model>Meta-clay>Add System to create a new meta-clay system. Go to Model>Info>Selection and call it meta1.

Now you need to add meta-clay balls to the system. The easiest way is to go to Model>Meta-clay>Add Element to get the first ball, and then to Model>Duplicate>Repetition to add the extra balls. Set the number of occurrences to 69 and make sure the transformations are neutral (0 for translation and rotation and 1 for scale). Hitting clean all in the schematic will display your new meta-clay system.

To add the BPF to the meta-clay, first select the root of the meta-clay system (the top-most null that we called meta1). Go to Motion>FcrvEdit>gowiththeflow+ to activate the go with the flow plugin. Click the Select Particle .bpf File tab and navigate to the smoke.bpf file we made earlier in particle. Next, hit the Read File bar. It will go through some craziness while it reads the BPF file. You'll notice that it tells you how many particles are in the animation. That's how you will know how many meta-clay elements you need in the scene. Make sure that the only option checked is the 'Set frame start, end, step' field. Click the GO! Button at the bottom of the Go With the Flow window.

Now you will have a nice little smoke trail in your Softimage scene. If you render it out now it will look O.K., but something will be not quite right. That's because we still need to adjust the scaling of the balls and add anime style-shading to them.

Since smoke usually starts from a single source and eventually grows larger as it dissipates into the air, you'll need to keyframe the scaling of the meta-clay elements as the animation progresses.

To scale the meta-clay, go to frame 100 and multi-select all the meta-elements. Right-click on the mouse and slide the time slider down to frame 30. Hit Motion>SaveKey>Object>Scaling>All. Then slide the slider down to frame 1. Enter a scaling of .1 for X, Y and Z on frame 1 and save the scaling again. Now when you scrub through the animation the smoke will look more natural. (Hint: you need to start on 100 and then right-slide down to 30 save key, and then to 1 and save the key. If you don't right-slide, the keys for the hidden balls won't be saved!)

rendering the "cel" look
When you are satisfied with the motion and scaling of the meta-ball elements, it is time to add the material and render.

Select the meta-system (meta1) and go to Material>Material. Choose the Lambert shading model and just leave the color that default grey. Then in the mental Ray field, check the Material Shader box and choose the Toon shader from the Shader_lib database. Click Edit to edit the shader. In the Toon shader window, be sure that the color option is selected in the color field and then click OK twice to exit the material area . (toon1.tiff)

Render off your images and pat yourself on the back, because now you're well on your way to having a beautifully rendered anime smoke trail.

After the final images are rendered, there are just a few more steps to achieve the completed cel look. One solution is to render the scene again using mental ray and activating the contour rendering box in the option menu. Another option is to use the "FIND EDGE" filter in Photoshop to outline the smoke images as well as the area where the ambient and diffuse colors meet. Once this is done, you can "multiply" the outlined images to your colored images using a compositing program such as Softimage's Eddie, Alias' Composer, and anything else at hand that has the capability.

click here to download a short avi showing the final result of this article


Peter Arisman is a digital artist working and living in Seattle. He can be contacted at parisman@lith.com and has a web site at www.3dartists.com.


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