- Apr 19, 2002
Common Particle Parameters
Each class of particle system in 3ds max 4 has a common set of parameters that are used to control aspects of the particle system.
The following sections describe the parameters common to each class of particle system, both Simple and Super.
Simple Particles: Spray and Snow
Spray and Snow share most parameters; Snow particles have rotation parameters and Spray particles do not. The following are parameters for the Simple Particles:
Viewport and Render Count. These parameters control the total number of particles that are emitted over time with regard to viewport display and render display. The main purpose for these related parameters being uncoupled is that the user can work faster in the viewports by displaying only a portion of the total particle count, while still rendering with a full quantity.
Drop Size. This parameter controls the scale of the particle geometry.
Speed and Variation. These are a bit misleading. Speed determines the velocity of the particles at birth, and Variation not only varies the speed value but also implements a sort of spreading pattern, with higher values increasing the spread.
Tumble and Tumble Rate. These are rotational parameters added to Snow. Tumble controls the amount of rotation of the particles and Tumble Rate controls the speed at which the particles rotate.
Render Tetrahedron and Facings. These parameters are the given particle primitives or predetermined geometry for the particles. Tetrahedrons are shaped like simple raindrops, and Facings are square polygons.
Start and Life. These parameters control particle birth and death. Start determines the start frame of particle emission in absolute time, and Life is a relative value that determines how many frames a particle is "alive." Life is relative, because particles are constantly born and emitted, starting on the Start frame and continuing forever, so a particle born at frame 100 with a life of 60 dies at frame 160.
Birth Rate and Constant. These parameters are used to pulse or burst emit particles, a simple method that is expanded by the Super Particles. Birth Rate determines the amount of particles emitted in a given round. When activated, the Constant check box disables the Birth Rate parameter.
Super Particles: SuperSpray, Blizzard, PCloud, and PArray
The Super Particles class of particle systems share many common parameters. In fact, SuperSpray, Blizzard, PCloud, and PArray are primarily differentiated by how they handle emitters. The following are parameters for the Super Particles:
Icon Size and Emitter Hidden. These parameters are cosmetic values that control the size of the emitter icon and determine whether it is hidden or displayed.
Dots, Mesh, Ticks, and Bbox. These parameters are the viewport display methods for particles. Dots vary depending on the viewport display method used (Heidi dots are single-pixel and OpenGL dots are much larger). Mesh displays the actual geometry to scale in the viewports, a method that tends to be computationally intensive but still useful. Ticks, like Dots, are constant in size with the exception of being shaped like crosses. Bbox displays the bounding box of the particle geometry. This is often faster than using the Mesh method.
Percentage of Particles. This parameter controls the percentage of actual particles displayed in the viewports. This does not affect the quantity of particles at render time, but is used to speed up display by reducing the number of particles the display has to render.
The Super Particles class was added in release 2 and builds on the previous particle systems, Spray and Snow. The main difference between the four Super Particle systems is the way in which they emit particles. Common particle generation parameters are as follows:
Use Rate and Use Total. These parameters are the primary methods for controlling the amount of particles emitted. Use Rate determines a variable number of particles that are emitted at each frame. Use Total defines a total quantity of particles that the system can emit over time, the rate of which depends on the emission start and stop time.
Speed and Variation. These parameters control the emission velocity of the particles. Variation controls the percentage at which Speed will be varied on a particle-by-particle basis. You use Variation as a common parameter with many particle systems because it's useful to break up the uniformity of values by adding some randomness to them.
Emit Start and Stop. These parameters are the set frame numbers at which particles will start to be emitted and will stop.
Display Until and Life. These parameters are used to determine when particles will die. Display Until is a rudimentary way of doing this absolutely so that on a given frame all particles will die. Life is like Spray, a relative value determining how many frames a particle will be present after it's been emitted.
Size, Grow For, and Fade For. These parameters control particle geometry scale. Size is a multiplier of scale and has a Variation parameter tied to it to randomize the scale on a particle-by-particle basis. Grow For and Fade For are two parameters that cause particles to grow from a scale of zero to the full Size value and then fade to zero over a given set of frames.
Seed. This parameter is an important random value that controls the uniqueness of particle systems. It's a random number that can be changed using the New button next to it. If multiple particle systems use the same Seed value, they emit particles identically. Use different Seed values to cause variation among particle systems.
The Super Particles class of particle systems shares three main types of geometric representations: Standard, MetaParticles, and instanced geometry. PArray contains a fourth type called Object Fragments.
Standard, MetaParticles, and instanced geometry determine the types of geometry the particles will be displayed as:
Standard. This type offers several particle primitives, such as Triangle, Cube, Facing, and Sphere.
MetaParticles. These are a special type of geometry primitive that is useful in creating amorphous liquid shapes. MetaParticles create spheres at each particle location, and then fuse the geometric surfaces together when their proximity to one another passes a user-defined threshold. When MetaParticles are sparsely spaced they appear as simple spheres, but when packed closely together they fuse into blob shapes. This is computationally expensive and should be used with extreme care.
Instanced Geometry. This is a useful particle type that enables the user to reference separate objects in the scene as particle geometry. For example, a single teapot object can be referenced and will cause instances of the teapot to be emitted as particles. The instanced geometry can also be hierarchically animated, enabling effects such as swimming fish and flocking birds.
Rotation and Collision
All the Super Particles share the same set of Rotation and Collision controls, which specify the speed of rotation and starting angles. Collision is a bit misleading, because it has to do with particle-to-particle collisions only, not with objects in the scene. The following are Rotation and Collision controls:
Spin Time and Phase. These control the amount of frames it takes for a particle to fully rotate, with low values causing faster spinning. Phase determines the starting angles of rotation.
Random, Direction of Travel, and User Defined. These are three methods for controlling rotation. Random rotates the particles on varied axes. Direction of Travel forces the particles to orient themselves in the direction they are traveling, with an optional Stretch value to actually stretch the particle geometry based on velocity. User Defined sets an absolute rotational axis in X,Y, and Z.
Interparticle Collisions. This is a set of parameters to test particle-to-particle collisions. This is computationally intensive and useful only in rare instances. Calc Intervals Per Frame is a parameter for controlling the rate at which the particle collisions are tested. Bounce is a percentage of force applied at collision.
Object Motion Inheritance
Object Motion Inheritance controls how much velocity is passed from the emitter to the particles. No motion inheritance causes the particle's speed to control velocity; 100% inheritance causes the full velocity of the emitter to be added to the particle emission speed. This is relevant only to a moving emitter. Object Motion Inheritance is a useful control for adding realism to particle motion. Unfortunately, the default value of 100% tends to confuse people. There are two controls:
Influence. This determines what percentage of the particles is affected.
Multiplier. This determines how much of the velocity is inherited from the emitter. A multiplier of 0 implies no inheritance, and 1.0 passes 100% of the emitter velocity to the particles.
Bubble Motion includes another set of parameters that are common to the Super Particles class of particle systems. These parameters are used to impart a wobbling motion to particles. Unfortunately, they aren't particularly intuitive and often require good viewport feedback to properly visualize. There are three main parameters to control Bubble Motion:
Amplitude. This parameter controls the distance at which the particle will wobble away from its original direction.
Period. This parameter controls the cycle time of particle oscillation, which is similar to waveform frequency.
Phase. This parameter is used here similarly as it was with rotation, controlling the initial wobble offset.
All Super Particles have common controls for particle spawning. Particle spawning is the emission of particles from particles. There are several methods by which particles can be spawned over time:
None. This method causes zero particle spawning.
Die after Collision. This method causes particles to die when they collide with a Deflector space warp.
Spawn on Collision. This method performs the opposite of the previous method, causing particles to be born on collision.
Spawn on Death. This method causes a sort of fireworks effect by creating particle spawns when a particle dies.
Spawn Trails. This method is pretty self-explanatory, causing particles to spawn trails of new particles behind them over their lifetime.
Each of the spawning controls has common parameters used to control the events and the spawned particles:
Spawns. This parameter determines the number of particle spawns that happen over a particle's lifetime.
Affects. This parameter determines the percentage of particles that will produce spawning.
Multiplier. This parameter is a value that multiplies the number of particles spawned at a given event.
Directional Chaos. This parameter is used to vary the direction at which particles are spawned.
Speed Chaos. This parameter is similar to Directional Chaos, but instead varies the speed at which particles are spawned on a frame-by-frame basis.
Scale Chaos. This parameter is similar to Directional Chaos and Speed Chaos, but varies the scale of spawned particles.
Lifespan Queue. This parameter is used to determine several alternate lifetimes for spawned particles. Values are created and stored in the queue and then passed on to spawned particles on an event-by-event basis.
Object Mutation Queue. This parameter works with instanced geometry and causes spawn particles to switch between instanced geometry types referenced in the queue on an event-by-event basis.
Parameters Unique Among Super Particles
As mentioned earlier, the main differences between the Super Particles are the methods used to emit particles. These unique features are described in the following sections.
Blizzard includes the following values:
Width and Length. These are used to determine the size of the rectangular emitter object.
SuperSpray includes the following values:
Off Axis and Spread. These are two related values that control the angle of emission from a single point in space. Off Axis determines the angle off axis from Z (straight up through the emitter), similar to the elevation of a gun in a turret. Spread controls the angle at which particle emission is varied in a fan direction.
Off Plane and Spread. These are two more related values to control the angle of emission from a point. Off Plane controls the angle of emission rotated around the plane of the emitter, similar to the azimuth of a gun in a turret. Spread controls the conical spread angle along the axis of emission. A value of 180 creates a complete cone shape.
PArray is unique because it uses geometry for emitters and can explode that geometry into fragments to use as particle geometry:
Object-Based Emitter. This is a pickbutton used to determine which object will be used for emission.
There are several particle formation methods:
Over Entire Surface. This method creates particles evenly over the surface of the emitter geometry. This is the most commonly useful method and thereby the default.
Along Visible Edges. This method snaps particle emission to the visible edges of the emitter object.
At All Vertices. This method restricts emission to the vertices of the emitter object.
At Distinct Points. This method isolates particle emission to a given set of distinct points on the emitter's surface.
At Face Centers. This method emits particles from the centers of all faces on the emitter object.
Use Selected Sub-Object. This method is a check box that applies to all the previous methods. This enables the user to further restrict emission to only the selected sub-objects (faces, edges, verts) of the emitter geometry.
PArray has some unique parameters and methods for creating object fragments for particle geometry:
Thickness. This parameter determines the size of the fragments' extrusion.
The following three methods determine how an object will fragment:
All Faces. This method forces each face of the emitter geometry to be used as a polygonal fragment.
Number of Chunks. This method sets a minimum number of fragments created.
Smoothing Angle. This method controls the number of fragments created based on the angle of the surface normals of the emitter object. The higher the angle, the fewer the fragments created.
PCloud is unique because it emits particles from within a volume instead of a surface. There are four methods to define the volume:
Box Emitter. This method is a variable box shape controlled by length, width, and height.
Sphere Emitter. This method is a variable spherical shape.
Cylinder Emitter. This method is a variable cylindrical shape with parameters similar to Box Emitter.
Object-Based Emitter. This method uses selected geometry from the scene to use as a volume emitter.
PCloud has unique particle motion methods:
Random Direction. This method emits particles along random vectors.
Enter Vector. This method uses X,Y, and Z vectors to determine the exact emission direction.
Reference Object. This method uses a scene object's Z-axis as the target direction for particle emission.