‘Derezzing’ a crashing light cycle, part I: first test

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Probably the coolest effect in Tron is the ‘derezzing’ of light cycles after they crash into an ‘exhaust wall’. This effect didn’t end up being part of our Tron test animation. So I figured, I’d give it a go and create one anyway 🙂

Anyway, I did a first test setup of a single fragment that’s exploded of a crashed cycle. To figure out what happens during the violent ‘derezzing’ I closely looked at the original VFX test. A few days ago I also found links to Digital Domain’s making off video, which has in the mean time been removed again. However, I did have a close enough look at it to get some idea’s on what to do with my version of this effect. Unfortunately, Tron Legacy hasn’t been released to cinema’s in my little nook of the world (have to wait until Jan 19), so I haven’t had the chance to get better look at all the examples in the movie itself.

So, what I came up with is that when the bike crashes it fragments into ‘physical’ pieces and the energy source erupts in glorious glowing fluid flying all around (which fits nicely with the scene in the original Tron where Flynn, Ram and Tron drink from a source of pure energy, which is obviously a fluid). The ‘fragments’ of the cycle, now no longer held together by the ‘source’ start ‘derezzing’ violently.

These were the basic concepts to work with. As one has to start somewhere, I decided to do a first test with the ‘derezzing’ of fragments. The basis of this is the same fx animation I used for the ‘rezzing’, but now in reverse. This is setup so that the effect spreads from the cutting plane that cut the fragment off the cycle, which can be nicely achieved using an ‘attribute transfer’ from the actual plane that is used to cut the geometry of the cycle in pieces.

So far, it was possible to use the effect I already had done. However, as the faces fly off the fragment, at some point they ‘lose integrity’ and they fly off in a dynamic simulation.

In this version of the effect I have not yet included the wire frame creeping over the surface ‘in front’ of the faces coming off. I will add that effect as well in coming versions. However, partly based on what I think I’ve seen in the Digital Domain making of, I decided to add a bit more violence to the ‘derezzing’, that differentiates it more from the controlled ‘rezzing’. Coming back to the energy that keeps all things together in the Tron universe, I thought it would be cool if ones a fragment is ripped of a bike, the energy that hold together the faces of the fragment starts releasing violently resulting in the faces to separate. So, I decided to add a particle animation to the fragment where its faces are just separating, to represent this energy to fly off in ‘sparks’. In a following version this will be preceded by the wire frame appearing just in front, further tying it all toegether.

So here’s a first break down render. This render shows a fragment being launched into the sky (will eventually be a dynamic sim as well, not its just key framed), where the fragment ‘derezzes’. It shows three levels of the render. First without ‘spraks’, then with ‘sparks’ and then a version where the sparks have gotten a basic glow treatment.

View in full resolution: trnd_crash_breakdown_v01.

You can clearly see the difference in ‘dynamic’ behavior of the bigger fragment and the facets coming off, which is mostly a result of the first being hand animated and clearly doing things that wouldn’t happen in a real gravity field. This should be better once the fragments themselves are also simulated after getting an initial animated ‘art direction’. The motion blur is also still a bit weird, but I haven’t really looked much at rendering at this point.

Next steps for this new animation will be:

  • creating a two cycle animation (including a upgraded exhaust wall effect)
  • creating the dynamics sim (started off with hand animated initial fragment movement) for the fragments
  • add the current ‘derez’ system to each fragment
  • adding the ‘energy source’ fluid explosion
  • comping it all together

You might have noticed, if you’ve read my posts on my breaking wave system, that these Tron posts are a lot less detailed in the Houdini technicalities of the effects. The reason for this is simply time. There’s always too little of the nasty thing. Anyway, I’m typically willing to go into more detail on specifics on request.

Ok, that’s it for this update. More will follow…