INSIDE 3DS MAX® 7 [Electronic resources] نسخه متنی

Elements of a Particle System

When a rocket emits a fiery trail, there is a point from which the smoke and fire spawn. In max this is the emitter. An emitter represents the location at which particles will be created, and it can occupy a single point in space, the surface of an object or helper, or a volume. Emitters can be animated, passing their movement properties to the particles they spawn (Figure 17.3). In the case of a rocket's trail, emitted sparks may inherit the rocket's momentum and then drift off without being further influenced. In other cases, particle movement can be influenced by emitter movement well after a particle has been created, such as with a cloud of magical sparkles surrounding a gesturing wand.

The leaves, sparks, or dancing apples in your scene are, of course, the particles themselves. Particles are spawned by emitters, and they can be rendered using a variety of simple geometric shapes (spheres, tetras, or cubes) or flat polygonal shapes (sixpoint, triangles, and a hybrid shape named "Special" that consists of three intersecting polygons which together approximate a low-poly version of a geometric shape). Most often these low-poly particle representations are used when creating atmospheric or special effects, where the main visual impact will be conveyed through the materials used (Figure 17.4).

Note

When creating an effect that will depend on a large number of fine particles, such as vapor or rain, try to use the simplest appropriate particle shape to keep max from getting bogged down from calculating an excessive amount of particle geometry.

One of the more visually impressive particle effects is the creation of flowing liquids, such as water, lava, or the shape-changing T-1000 in Terminator 2: Judgment Day. When you're creating liquid effects, the MetaParticle shape can be very effective. With this type, particles represent points within a metaball, or blob object. The coarseness and tension of the metaball effect can be varied to achieve the desired smoothness. While the MetaParticle shape is capable of creating just about any type of liquid effect that can be animated using non-event-driven particle systems, a more powerful metaball feature is available in the BlobMesh compound object (Figure 17.5).

BlobMesh can use geometry as well as particles to create metaball effects. Later in this chapter, you will explore the use of BlobMesh in event-driven particles.

When your scene calls for swarms of flying bats, crawling centipedes, or diving jet fighters, the instanced geometry particle type is your best choice. Possibly the most sophisticated particle representation, the instanced geometry particle can take on nearly any modeled shape, even animated and hierarchical groups. This technique is often used for flocking creatures and large fleets of similar objects, or in situations where the other particle types are insufficient (Figure 17.6).

A big part of the excitement and believability of particles is in their interaction with forces of nature, such as gusting wind or explosive waves, or with unnatural forces, like tractor beams or force fields. The speed and direction of particles within a system can be influenced by several kinds of forces. Forces such as Gravity, Drag, and Wind can be used to create naturalistic particle movement. Other forces, such as Push, Motor, Vortex, and Displace are especially appropriate for special effects and unnatural influences. The PBomb space warp is a specialized tool for applying an explosive dispersal to particles. For exacting control of particles along a spline path, the Path Follow force allows particles to converge on a path, diverge from it, or follow it throughout their life span. Using forces to influence the behavior of your particles is a handy way to add believability in an easy procedural fashion.

Deflectors are another type of particle influence, and they are useful in situations where particles need to interact with scene objects. Imagine beads bouncing off and around a stack of blocks, or a laser being redirected by a lens. Deflectors can cause particles to bounce, refract, react to friction, and alter their speed or path. The shape of deflectors can be based on simple helper objects, such as planes or spheres, as well as on instanced geometry. The shape, size, and location of deflectors can also be animated to simulate moving obstacles, such as a sailing ship displacing fog.

Particle systems in max are available in two distinct types: event-driven (Particle Flow) and non-event-driven (the legacy particle systems such as Blizzard, Spray, and PArray). Each will be discussed in turn in the next two sections.