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Dynamics

List of particle attributes

The following table gives a summary of the particle shape node attributes you can set or examine in expressions or MEL. The attributes affect the particle object within which they exist. For more details on the attributes, use this book’s Index. Note these issues:

• The table shows attribute spellings required in expressions and MEL. User interface spellings typically use capital letters and spaces between words.
• Attributes with a data type of vector array or float array are per particle attributes. All other attributes are per object attributes. For details on data types, see Expressions and the online MEL documentation.
• Attributes marked by an asterisk (*) are dynamic attributes that exist only if you or Maya add them to the object. Attributes that list the attribute’s short name in parentheses exist in each particle object by default.
• If you are an API developer, be aware that there are more attributes described in the online documentation. Use your internet browser to go to the main Maya documentation page, then go to the Dependency Graph Nodes page, and finally to the Particle page.
• The table omits the compound attributes centroid and worldCentroid. Compound attributes consist of two or more component attributes. The centroid attribute consists of centroidX, centroidY, and centroidZ attributes. The worldCentroid attribute consists of worldCentroidX, worldCentroidY, and worldCentroidZ You can use compound attributes with MEL commands such as setAttr. For details, see the online MEL documentation.

Attribute long name (and short name)	Description	Data Type
acceleration (acc)	Sets the rate of change of velocity on a per particle basis.	vector array
age (ag)	Contains the number of seconds each particle in the object has existed since the first frame. This is a read-only attribute.	float array
attributeName*	Specifies the name of the attribute whose values are to be displayed at particle positions. By default, particle id numbers are displayed. Valid for Numeric render type.	string
betterIllumination*	Provides smoother lighting and shadowing at the expense of increased processing time. Valid for Cloud render type.	boolean
birthPosition	Stores the position at which each particle was born in the particle’s local space.	vector array
birthTime (bt)	Contains the Current Time value at which each particle in the object was created. This is a read-only attribute.	float array
cacheData (chd)	Turns on or off dynamic state caching for the object.	boolean
castsShadows (rsh)	Turns on or off the object’s ability to cast shadows in software rendered images. Valid for Cloud, Blobby Surface, and Tube render types.	boolean
centroidX, centroidY, centroidZ (ctdx, ctdy, ctdz)	Contains the X, Y, and Z elements of the average position of its particles. These are read-only attributes.	float
collisionFriction (cfr)	Sets how much the colliding particle’s velocity parallel to the surface decreases or increases as it bounces off the collision surface. This attribute is displayed as Friction in the user interface. It works on a per geometry basis.	float (multi)
collisionResilience (crs)	Sets how much rebound occurs when particles collide with a surface. This attribute is listed as Resilience in the user interface. It works on a per geometry basis.	float (multi)
collisionU, collisionV*	U and V positions of the NURBS surface where a particle collided in the current frame. For polygonal surfaces, the values are always 0. The values are reset to -1 at the start of each frame. Values change only in frames where collision occurs. These are read-only attributes.	float
colorAccum*	Adds the RGB components of overlapping particles. Also adds opacity values of overlapping particles. Generally, colors become brighter and more opaque as they overlap. To see the effect of Color Accum, you must add an opacity attribute to particles displayed as Points. Valid for MultiPoint, MultiStreak, Points, and Streak render types.	boolean
colorBlue*	Sets blue component of RGB color. Valid for all render types except Numeric and Tube.	float
colorGreen*	Sets green component of RGB color. Valid for all render types except Numeric and Tube.	float
colorRed*	Sets red component of RGB color. Valid for all render types except Numeric and Tube.	float
conserve (con)	Sets how much of a particle object’s velocity attribute value is retained from frame to frame.	float
count (cnt)	Contains the total number of particles in the object. This is a read-only attribute.	integer
currentTime (cti)	Sets the time value for the particle object’s independent clock.	time
depthSort (ds)	Turns on or off depth sorting of particles for rendering. This prevents unexpected colors when you hardware render overlapping colored, transparent particles. Valid for MultiPoint, MultiStreak, Points, Streak, and Sprites render types.	boolean
dynamicsWeight (dw)	Scales the effect of fields, collisions, springs, goals, and emission on particles.	float
emissionInWorld (eiw)	When on, emission occurs in the world coordinate system. This is the default setting. When off, emission occurs in the emitted particle object’s local space.	boolean
emitterRatePP*	Sets the per particle emission rate.	float array
enforceCountFromHistory (ecfh)	In a soft body, if you change the original geometry’s construction history in a way that alters the number of CVs, vertices, or lattice points, Maya updates the number of particles of the soft body correspondingly.	boolean
event*	Contains the number of times each particle in the object has hit something. This is a read-only attribute.	float array
expressionsAfterDynamics (ead)	Sets whether expressions are evaluated before or after other dynamics.	boolean
force (frc)	Contains the accumulation of all forces acting on the particle object. This is a read-only attribute. If you use this attribute in an expression, first turn on expressionsAfterDynamics.	vector array
forcesInWorld (fiw)	Sets whether forces are applied to the object in world space or in its local space.	boolean
goalActive (ga)	For a goal object, turns each goal on or off. It has the same effect as setting the corresponding goalWeight to 0, except the animation processing is more efficient. This attribute works on a per object basis.	boolean (multi)
goalOffset*	Sets an offset to the world space position of the goal object.	vector array
goalPP*	Sets how much the particles try to follow the goal on a per particle basis.	float array
goalSmoothness (gsm)	Sets how smoothly goal forces change as the goal weight changes from 0 to 1. The higher the number, the smoother the change.	float
goalU, goalV*	Set the exact locations on a NURBS surface where the particles are attracted.	float array
goalWeight (gw)	Sets how much all particles of the object are attracted to the goal.	float (multi)
incandescencePP*	Sets glow color in conjunction with a software rendering Particle Incand Mapper Node (see Rendering.) Valid for Cloud and Tube render types.	vector array
inheritFactor (inh)	Sets the (decimal) fraction of velocity an emitted particle object inherits from an emitter.	float
inputGeometrySpace (igs)	For a soft body, this sets the coordinate space Maya uses to position point data provided by the input geometry to the particle shape.	integer
isDynamic (isd)	Turns on or off dynamic animation of the object.	boolean
isFull (ifl)	Contains 1 if an emitted particle shape is full, or 0 if not full. An emitted particle shape is full when the number of emitted particles equals the maxCount. This is a read-only attribute.	boolean
lifespan*	Sets when all particles in the object die.	float
lifespanPP*	Sets when particles die on a per particle basis.	float array
levelOfDetail (lod)	Scales the number of particles that can be emitted into the emitted particle object.	float
lineWidth *	Sets the width of streaking particles. Valid for MultiStreak and Streak render types.	float
mass (mas)	Specifies the physical mass of particles. Mass values affect the results of dynamic calculations. By default, each particle of a particle object has a mass of 1.	float array
mass0 (mas0)	Initial state counterpart to mass.	float array
maxCount (mxc)	Sets a limit on the number of particles the emitted particle shape accepts from an emitter.	int
multiCount*	Sets number of points you want displayed for each particle in the object. Valid for MultiPoint and Points render types.	float
multiRadius*	Sets radius of spherical region in which particles are randomly distributed. Valid for MultiPoint and MultiStreak render types.	float
needParentUV*	Turns on or off the ability to read the parentU and parentV attributes. If you add a surface emitter to a NURBS or polygonal surface, parentU and parentV contain the UV coordinates where each particle was emitted. You can use these attributes in expressions and MEL scripts.	boolean
normalDir*	Sets direction of normal for particles. Use with useLighting. Valid for MultiPoint, MultiStreak, Points, and Streak render types.	integer (1-3)
opacity*	Sets amount of transparency for all particles in the object. Valid for all render types except Numeric and Tube.	float
opacityPP*	Sets amount of transparency on a per particle basis. Valid for all render types except Numeric, Tube, and Blobby Surface.	float array
particleId (id)	Contains the id number of each particle. Valid for Numeric render type. This is a read-only attribute.	float array
parentId*	If you emit from a particle object, this contains the id of all particles that emit the particles. You can use the id to query the emitting object’s attribute values, for example, acceleration, velocity, and lifespanPP. This is a read-only attribute. Note that if you use the MEL emit command to create the particles that emit, the parentId attribute of those emitted particles is always 0.	float array
parentU, parentV*	If you add a surface emitter to a NURBS or polygonal surface, these attributes contain the UV coordinates where each particle was emitted. To use these read-only attributes, you must turn on Need Parent UV in the emitter. You can use these attributes in expressions and MEL scripts.	float array
particleRenderType*	Sets render display type of particles, for example, Streak.	integer
pointSize*	Sets how large particles are displayed. Valid for MultiPoint, Numeric, and Points render types.	float
position (pos)	Sets the object position in local space coordinates on a per particle basis.	vector array
position0 (pos0)	Initial state counterpart to position.	vector array
radius*	Sets radius size of all particles. Valid for Blobby Surface, Cloud, and Sphere render types.	float
radius0*	Sets starting point radius for Tube render type.	float
radius1*	Sets ending point radius for Tube render type.	float
radiusPP*	Sets radius size on a per particle basis. Valid for Blobby Surface, Cloud, and Sphere, render types.	float array
rampAcceleration (rac)	Controls acceleration with a ramp. Any other animation of acceleration is added to the ramp-controlled acceleration.	vector array
rampPosition (rps)	Controls position with a ramp. Any other animation of position is added to the ramp-controlled position.	vector array
rampVelocity (rvl)	Controls velocity with a ramp. Any other animation of velocity is added to the ramp-controlled velocity.	vector array
rgbPP*	Sets color on a per particle basis. Valid for MultiPoint, MultiStreak, Points, Spheres, Sprites, and Streak render types.	vector array
seed (sd)	Sets the id of the random number generator of the associated emitter. This attribute works on a per object basis.	float (multi)
sceneTimeStepSize (sts)	Contains the value of the time difference between the last displayed frame and current frame. This contains 1 if you’re simply playing the animation or clicking the frame forward or backward button. If you click widely separated frames in the Time Slider, the attribute contains the difference in time between the two frames. This is a read-only attribute.	time (in current units)
selectedOnly*	Turns on or off display of id numbers only for selected particles. Valid for Numeric render type.	boolean
spriteNum*	Sets the image number index for a Sprite image sequence.	integer
spriteNumPP*	Sets the image number index for a Sprite image sequence on a per particle basis.	integer array
spriteScaleX, spriteScaleY*	Sets the Sprite X- and Y-axis image scale.	float
spriteScaleXPP, spriteScaleYPP*	Sets the Sprite X- and Y-axis image scale on a per particle basis.	float array
spriteTwist*	Sets the Sprite image’s rotation angle.	float
spriteTwistPP*	Sets the Sprite image’s rotation angle on a per particle basis.	float array
startFrame (stf)	Sets the animation frame after which dynamics (including emission) are computed for the object.	float
surfaceShading*	Sets how sharply the spheres of Cloud render type are displayed. Use a value between 0 and 1. A value of 1 displays spheres more distinctly; a value of 0 creates a cloudier effect.	float
tailFade*	Sets the opacity of tail fade. Valid for MultiStreak and Streak render types.	float
tailSize*	Sets the length of the tails for MultiStreak, Streak, and Tube render types.	float
targetGeometrySpace (tgs)	For a soft body, sets the coordinate space Maya uses to position point data provided by the particle shape to the target geometry.	integer
threshold*	Controls surface blending between Cloud or Blobby surface spheres. This is a read-only attribute.	float
timeStepSize (tss)	Contains the animation frame increment in current units. For example, if your animation is set to Film (24 fps), timeStepSize has a value of 1 (frame). Keying or otherwise setting the Current Time value alters the timeStepSize. For instance, with a frame rate of 24 frames per second, suppose you set the Current Time to 0 at frame 0, and to 100 at frame 50. Because you’re compressing twice as much time between frames 0 and 50, the timeStepSize is twice as large, in other words, 2. This is a read-only attribute.	time
totalEventCount (evc)	Contains total events that have occurred for all particles of the object. This is a read-only attribute.	integer
traceDepth (trd)	Sets the maximum number of collisions Maya can detect for the object in each animation time step.	integer
traceDepthPP*	Sets the trace depth on a per particle basis.	float array
UseCurrentUVSet	Selects the UV set on the poly emitter that is used for textured emission effects. The same UV set is used for all textures attached to all textured emission effects (color/opacity and emission rate). If the UseCurrentUVSet option is selected, then the active UV set on the surface emitter is used.	boolean
useLighting*	Turns on or off whether scene lighting lights up particles. Valid for MultiPoint, MultiStreak, Points, Sprites, and Streak render types.	boolean
userScalar1PP userScalar2PP userScalar3PP userScalar4PP userScalar5PP	Predefined outputs for user-defined attributes used in Particle Sampler Info node.	float array
userVector1PP userVector2PP userVector3PP userVector4PP userVector5PP	Predefined outputs for user-defined attributes used in Particle Sampler Info node.	vector array
velocity (vel)	Sets speed and direction on a per particle basis.	vector array
velocity0 (vel0)	Initial state counterpart to velocity	vector array
visibleInReflections (rrl)	Turns on or off whether the object is visible in reflections when software rendered. Valid for Cloud, Blobby Surface, and Tube render types.	boolean
visibleInRefractions (rrr)	Turns on or off whether the object is visible in refractions when software rendered. Valid for Cloud, Blobby Surface, and Tube render types	boolean
worldBirthPosition	Stores the position at which each particle was born in world space.	vector array
worldCentroidX, worldCentroidY, worldCentroidZ (wctx, wcty, wctz)	Contains the world space X, Y, and Z elements of the average position of its particles. These attributes are a read-only attributes.	float
worldPosition (wps)	Contains the world space counterpart to position. This is a read-only attribute.	vector array
worldVelocity (wvl)	Contains the world space counterpart to velocity. This is a read-only attribute.	vector array
worldVelocityInObjectSpace (wvo)	Contains the local space equivalent to the object’s world space velocity. This is a read-only attribute.	vector array

Section of Attribute Editor	Contents
General Control Attributes	Attributes that set various operation characteristics of the entire particle object. These attributes are described in various places: Is Dynamic See Create rigid bodies. Dynamics Weight See Scale the effect of dynamics. Conserve See Adjust frame-to-frame velocity conservation. Forces In World See Apply forces in an object’s local space. Expressions After Dynamics See Control execution time of particle dynamics. Cache Data See Memory caching. Count See Attribute long name (and short name). Total Event Count See Attribute long name (and short name)
Emission Attributes	Attributes that determine some of the behavior of particles that are emitted. See Edit particle attributes. Also see the Emitter tab in the Attribute Editor of more attributes that affect emitted particle behavior.
Lifespan Attributes	Attributes that determine the particle lifespan, which can make particles disappear from the scene after they reach a specified age. Lifespan is typically used with emitted particles. See Set particle lifespan.
Time Attributes	Attributes that set the start frame and timing of dynamic influences on particles. See Change the start frame for a particle object and Control the timing of particle dynamics.
Collision Attributes	Attributes that set how precisely collision detection occurs. See Avoid unexpected particle penetration of geometry.
Soft Body Attributes	Attributes for advanced users who want to tune soft body effects (see Chapter 4, "Soft and Rigid Bodies").
Goal Weights and Objects	Attributes you can set if you add a goal to an object and connect it to a particle object or soft body. See Goals.
Instancer (Geometry Replacement)	Attributes that affect geometry instanced to animated particles. See Instance geometry to particles (single and animated).
Particle Seeds	Attributes that alter the random number stream used by Maya to create the random positions of emitted particles. See To make particles live forever.
Render Attributes	Attributes that affect how particles are displayed and rendered. See Choose how particles render.
Render Stats	Attributes that set aspects of particle software rendering. See Add reflections, refractions, and shadows.
Per Particle (Array) Attributes	Attributes you can set on an individual particle basis for several commonly used motion and display features. See Per particle and per object attributes and Set attributes on a per particle basis.
Add Dynamic Attributes	Buttons for adding attributes that control commonly desired features (see Add dynamic attributes).
Extra Attributes	Any custom per object attributes you’ve added. See Per particle and per object attributes.

Add Attributes For Current Render Type button

The added attributes follow:

Color Accum

Adds the RGB components of overlapping particles. Also adds opacity values of overlapping particles. Generally, colors become brighter and more opaque as they overlap. To see the effect of Color Accum, you must add an opacity attribute to particles displayed as Points. See Set particle opacity.

Normal Dir

Lets you tune the illumination of moving particles lit by a light added to the scene. See Use lights with moving particles for more details.

Point Size

Sets the size of the particle points. Point size is unaffected by camera distance. Both far and near particles appear the same size in the workspace.

Use Lighting

Illuminates particles using lights added to the scene. See Use lights with moving particles

Note After you add attributes for a particle render type, you can change the render type and add its default Particle Render Type attributes. Any attributes that don’t apply to the new render type are dimmed.

Add Attributes For Current Render Type button

The added attributes follow:

Color Accum

Adds the RGB components of overlapping particles. Also adds opacity values of overlapping particles. Generally, colors become brighter and more opaque as they overlap. To see the effect of Color Accum, you must add an opacity attribute to particles displayed as MultiPoint. See Set particle opacity.

Multi Count

Sets the number of points you want displayed per particle.

Multi Radius

Sets the radius of the spherical region within which the particles are randomly distributed.

Normal Dir

Lets you tune the illumination of moving particles lit by a light added to the scene. See Use lights with moving particles for details.

Point Size

Sets the size of the particle points. Point size is unaffected by camera distance. Both far and near particles appear the same size in the workspace.

Use Lighting

Illuminates particles using lights added to the scene. See Use lights with moving particles for details.

Add Attributes For Current Render Type button

The added attributes follow:

Color Accum

Adds the RGB components of overlapping particles. Also adds opacity values of overlapping particles. Generally, colors become brighter and more opaque as they overlap.

Line Width

Sets the width of each streak.

Normal Dir

Lets you tune the illumination of moving particles lit by a light added to the scene. See Use lights with moving particles for details.

Tail Fade

Sets the opacity of the tail fade, from 0 to 1. A value of 1 makes the tail completely opaque; a value of 0 makes the tail transparent.

Tail Size

Scales the length of the tail. A value of 1 gives the default length. Values less than 1 shorten the tail; values greater than 1 lengthen the tail.

Use Lighting

Illuminates particles using lights added to the scene. See Use lights with moving particles for details.

Add Attributes For Current Render Type button

The added attributes follow:

Color Accum

Adds the RGB components of overlapping particles. Also adds opacity values of overlapping particles. Generally, colors become brighter and more opaque as they overlap.

Line Width

Sets the width of each streak.

Multi Count

Sets the number of points you want displayed per particle.

Multi Radius

Sets the radius of the spherical region within which the particles are randomly distributed.

Normal Dir

Lets you tune the illumination of moving particles lit by a light added to the scene. See Use lights with moving particles for details.

Tail Fade

Sets the opacity of the tail fade, from 0 to 1. A value of 1 makes the tail completely opaque; a value of 0 makes the tail transparent.

Tail Size

Scales the length of the tail. A value of 1 gives the default length. Values less than 1 shorten the tail; values greater than 1 lengthen the tail.

Use Lighting

Illuminates particles using lights added to the scene. See Use lights with moving particles for details.