Particles Part 3

Written January 26th, 2009
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Deflectors are ways of controlling particle flow by preventing them from penetrating geometry that’s supposed to be solid. But why not have an option to prevent penetration of any polygons? Because the process can become processor intensive very, very quickly. While I’m not saying you need to use deflectors sparingly, you should give 3dsMax the luxury of some approximation. If your space-ship is a flying saucer, just approximate it with a squashed sphere.

That said, let’s have a look at the various deflector types! Imagine deflectors as a combination of 2 factors; shape and functionality.

Demonstrating deflector shapes.

Demonstrating deflector shapes.

There are three shapes in the deflector selection; spherical, planar, and universal. The first two are self-explanatory; they’re shaped as the name suggests. The universal deflectors are based on geometry that you specify. This means you can have that battle cruiser pushing asteroids out of the way perfectly. However, remember that this could tax your system heavily, so it’s a good idea to create a low-polygon mesh that can act as a proxy for the real 3d model.

In the image on the left, I show you how each of these shapes act. I’ve created mesh objects to represent the 3 deflectors in the render. The torus object is an approximated version using much fewer polygons than the rendered object has.


Next, there are three functional flavors of deflectors; ordinary, dyna-flect, and omni-flect. The first type of deflector is a highly simplified version of the deflector idea.  Think of these as similar to our spray versus super spray concept described earlier. The next, dyna-flect, is for use with reactor objects and other reactive bodies. You’d use it when you need the target object to respond to being struck by particles (like tank armor deflecting bullets but getting dented).

Very briefly, what makes omni-flect deflectors special compared to ordinary deflectors, is that they provide many additional features. Allow me to summarize them here:

  1. Reflection parameters – the ability to tweak how “bouncy” particles are as they strike the deflector.
  2. Refraction parameters – for particles that penetrate the deflector, you can chose to have some of them follow a “tweaked” bearing. Note that reflection is calculated before refraction, so if you wanted half of the particles reflected and then the other half refracted you’ll need to set 50% reflection and 100% refraction.
  3. Friction parameters – for glancing angles and particles that’ve come to rest on the deflector, the friction parameter helps them slow to a stop. This is useful for large numbers of objects subject to gravity.
  4. Spawn reactivity – for particles that have options controlling how they spawn on collision, these parameters let you tweak that for each deflector. For example, if your sparks strike concrete, they’ll break apart and spawn more sparks, whereas if they hit the welder’s clothing, they could just stick and then die in a few frames.


Forces allow you to direct the flow of 3dsMax particles without having to bounce them around with deflectors.  Think of forces as the “go here” command to the deflector’s “don’t go there” command.  You can combine forces to create very specific and complicated effects like galaxies, tornadoes, and harsh weather effects.

You create and bind these forces in the same way that you would for a deflector.  Just select the object, click-drag to create it in your scene, and then use the “Bind Spacewarp” tool to link it into your particle system.  Let’s take a look at each type of particle emitter in 3dsMax.  To aid in visualization, I’ve included some of the images from the help document.  I’m sorry I can’t include them all; there are a lot of space warps in 3dsMax!

  1. Push - Exactly as it sounds; this force will consistently push particles in a single direction.  This force is acceleration, so the older a particle is, the faster it’ll move!
  2. Motor - Operates similarly to the push force, but it applies a rotation at the same time.  Remember spin art? It’s a lot like that.  Because the “Motor” icon rotates your particles around it’s axis, the orientation is important!
  3. Vortex - Operates essentially like a push and a motor at the same time.  It applies a “swirling” motion in order to form a funnel similar to a tornado, black hole, or water spout.
  4. Drag - Lowers the speed of particles as they age.  You know how bullets slow down quickly as they enter water?  And that’s why action heroes always jump off the boat in order to get away from the bad guys?  That’s the effect that the drag force creates.
  5. Pbomb - Provides a shockwave that blows particles apart.  Very simple to implement because it is essentially only timing and intensity parameters.
  6. Path Follow – Forces particles to follow a spline as they move.  The key to remember here is that you can either have the particles follow the path as they exit the emitter, or follow the path as they come near a certain area.
  7. Gravity - Operates exactly as it sounds.  Gravity exerts a constant, uniform pull on all particles in a given direction.  You can also exert spherical gravity, which is very fun for modeling little galaxies and watching them congeal!
  8. Wind - Wind is a lot like gravity in that it applies an omnipresent, uniform force from a direction.  However, wind has many more options for simulating turbulence and non-uniformity over time.  In conjunction with snow or blizzard particle generators, you can make some very convincing weather effects.
  9. Displace - A very fun space warp.  The displace operation will deform both particle systems and geometry!  This is a big deal because it helps you bridge the divide between special, custom objects (like your character) and particles (like rain).

Learn more about advanced particle flow on the next page!

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