AFX Spell-Design Blog #4 (Chill Kill)

An Arcane-FX spell blog is long overdue, so here we go! The previous installment of this blog can be found at:
AFX Spell-Design Blog #3 (Fire Tower)

To escape the mighty Fire Tower we needed something cold and fast. And it had to be deadly. Hence "Chill Kill":


Check it out:
www.arcane-fx.com/visuals/blog4-movieA.avi <4mb>
www.arcane-fx.com/visuals/blog4-movieA.mov <4mb>

The idea is to mirror the design of "Great Ball of Fire", but with snow and ice. With a twist of his body the caster opens a portal ring around him. Hell has frozen over it seems, for out from the underworld comes snow, streaming up. It converges to point above him and forms into a ball of snow and deadly ice shards. The caster throws this ice-ball at his target, and upon impact it explodes. A field of deadly shards grows from the ground, and if his target is caught in them he is sent down cut and bloodied.


=== Casting Zodiac ===

Almost all the previous AFX spells start with a glowing reveal zodiac that is relatively static. This spell was fun though because I did things a little differently, using fast zodiac rotation accompanied by twisting orc animation to reveal the main zodiac effect. It's not as complete as one could imagine, mainly because there's no way to do animated masks. The vaguely arrow-shaped zodiac is intended as the "revealer":


The casting zodiac itself consists first of an underlayer that tries to simulates a cyclone or whirlpool. Although it spins in only one direction, there are two glowing zodiacs above it that spin in opposite directions, which helps to create a feeling of twisting and chaos. There are also some layers of snow zodiacs that spin in different directions, the snow caught in the hellish cyclone.

=== Streaming Snow Particles + Particle Transform Paths ===

I knew from the start I needed snow to pour out from the zodiac ring and up to a point above the caster. In retrospect this probably could have been accomplished with textured geometry, but I was thinking particles. But how was I going to get this shape?

One possibility was some kind of negative "black hole" force, but TGE forces seem largely built-in to component types, and there wasn't any model for creating new forces; plus, this kind of thing can be tricky even with Maya dynamics. Another possibility would be to take advantage of the emitter's "ejectionInvert" attribute, and with an offset cause particles to move back towards their emitter's center. I could imagine using a cone emitter and having the particles move towards the cones apex.

Still this would give me a very linear shape and I needed something smooth. So, I went ahead and added something Jeff and I have been meaning to add for a while: particle transform paths. Now I can specify paths along which emitted particles will travel across their lifetime, relative to each particles starting position. With a velocity (and gravity, etc.) of zero, the particles will follow the path perfectly, but with velocity (and gravity, etc.) the particles will diverge from the path.

There was still a problem though, because the shape of this snow-cloud wraps around the caster and hence the z-axis. I had to implement a "concentric" attribute, which cause the paths to be treated as revolved around the "vector" attribute axis relative to each particle. Now it was possible to treat the path like a profile in a revolve modeling operation. Here's the end result:


With these particle paths we're a step closer to doing effects-based characters!

=== Ice-Ball ===

The ice-ball is just textured geometry, with animation to make the ice shards shoot-out. But the the animation of the ice-ball itself is created with a series of AFX transform modifiers: I've added paths to get some wiggling, a spin modifier to get some spinning, and a scale modifier to increase its size. Using the timing parameters of each modifier I am able to create simple animations, and by layering a number of them the final, more complex motion is created.

To get the ice to glint, I created a separate dts model with dozens of little textured planes. Each plane is animated to scale up at a pseudo-random time, and this causes the flashing. This model was a little complex to set up, but it adds a nice touch. Here's an idea of the setup from Maya:


=== Field of Ice Shards ===

I like how these turned out:


The shards are just geometry, animated to scale up at different times. The texture and the reflectivity (environment mapping) are what help to sell the effect. Also, I created two collision boxes with opposing normals; one box will keep players from entering the field, while the other will trap the target inside! (I can't believe that actually worked...)

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Enjoy!

- Matthew Durante