LlParticleSystem

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Summary

Function: llParticleSystem( list rules );

Defines a particle system for the containing prim based on a list of rules.

• list rules Particle system rules list in the format [ rule1, data1, rule2, data2 . . . rulen, datan ]

Specification

Defines a particle system that sets the state of the particle emitter within the prim which the script is contained. Any other scripts in the same prim which call this function will modify the state of the same particle emitter. As such, the particle system defined by this function is a prim property, just like its size, shape, color, et cetera. Each prim has only one (1) particle emitter, located at its geometric center, and aligned along the prim's local Z-axis, pointing in the positive Z direction.

This is the only function which alters the state of the prim's particle emitter; thus, if you wish to change the emitter to a different state (i.e., emitting a different particle system entirely, or shut off the emitter completely), just call this same function with the parameters of the new particle system you wish to render instead. Specifying an empty list (i.e., llParticleSystem([]); ) turns the emitter off.

Particles are essentially 2D "sprites" and are always rendered facing the viewer's camera.

The rule / data values are defined below.

Rule / Value Constant Type Description Value
System Behavior
PSYS_PART_FLAGS integer}} hexadecimal|hex}} format, or by ORing together (using the | operator) one or more of the following flag constants: 0
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PSYS_PART_BOUNCE_MASK When set, specifies particles will bounce off a plane at the region Z height of the emitter. On "bounce", each particle reverses velocity and angle. This only works for particles above the plane falling down on it. 0x004
PSYS_PART_EMISSIVE_MASK When set, particles are full-bright and are unaffected by global lighting (sunlight). Otherwise, particles will be lit depending on the current global lighting conditions. Note that point lights do illuminate non-emissive particles. 0x100
PSYS_PART_FOLLOW_SRC_MASK When set, particles move relative to the position of the emitter. Otherwise, particle position and movement are unaffected by the position/movement of the emitter. This flag disables the PSYS_SRC_BURST_RADIUS rule. 0x010
PSYS_PART_FOLLOW_VELOCITY_MASK When set, particles rotate to orient their "top" towards the direction of movement or emission. Otherwise, particles are always emitted based on the current rotation of the emitter. 0x020
PSYS_PART_INTERP_COLOR_MASK When set, particle color and alpha transition from their START settings to their END settings during the particle's lifetime. The transition is a smooth interpolation. 0x001
PSYS_PART_INTERP_SCALE_MASK When set, particle size/scale transitions from its START setting to its END setting during the particle's lifetime. 0x002
PSYS_PART_TARGET_LINEAR_MASK (not officially documented) When set, emitted particles move in a straight line towards the target specified by the PSYS_SRC_TARGET_KEY rule. In this mode, PSYS_SRC_ACCEL, PSYS_SRC_BURST_RADIUS, and possibly other rules are ignored. 0x080
PSYS_PART_TARGET_POS_MASK When set, emitted particles change course during their lifetime, attempting to move towards the target specified by the PSYS_SRC_TARGET_KEY rule by the time they expire. Note that if no target is specified, the target moves out of range, or an invalid target is specified, the particles target the prim itself. 0x040
PSYS_PART_WIND_MASK llWind|wind}}. It is applied as a secondary force on the particles. 0x008
PSYS_PART_BEAM_MASK (unimplemented) mask but in the enum 0x200
PSYS_PART_DEAD_MASK Removes particles, not compatible with any other PSYS_PART_*_MASK 0x80000000
PSYS_PART_RANDOM_ACCEL_MASK (unimplemented) Presumed to be used to apply random acceleration to the particles. -
PSYS_PART_RANDOM_VEL_MASK (unimplemented) Presumed to be used to specify random velocity for the particles upon emission. -
PSYS_PART_TRAIL_MASK (unimplemented) Presumed to be used for implementing "trails" via emitting more particles at shorter bursts. -
System Presentation
PSYS_SRC_PATTERN integer}} Specifies the general emission pattern. 9
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PSYS_SRC_PATTERN_ANGLE Present particles in a 2-dimensional circular section as defined by PSYS_SRC_ANGLE_BEGIN and PSYS_SRC_ANGLE_END. The orientation of the particle plane is at X=0 relative to the emitter's region rotation. 0x04
PSYS_SRC_PATTERN_ANGLE_CONE Present particles in a 3-dimensional spherical section, as defined by PSYS_SRC_ANGLE_BEGIN and PSYS_SRC_ANGLE_END. 0x08
PSYS_SRC_PATTERN_ANGLE_CONE_EMPTY (not officially documented; appears to be non-functional) Present particles in a 3-dimensional spherical section, as defined by PSYS_SRC_ANGLE_BEGIN and PSYS_SRC_ANGLE_END, but inversely compared to the ANGLE_CONE pattern (i.e., where there were voids in ANGLE_CONE, there are particles in ANGLE_CONE_EMPTY, and vice-versa. 0x10
PSYS_SRC_PATTERN_DROP Present particles by dropping them at the emitter position with no force. Ignores the PSYS_SRC_BURST_RADIUS, PSYS_SRC_BURST_SPEED_MIN, and PSYS_SRC_BURST_SPEED_MAX rules. 0x01
PSYS_SRC_PATTERN_EXPLODE Present particles by shooting them out in all directions according to the burst motion rules. 0x02
PSYS_SRC_BURST_RADIUS float}} Specifies the distance from the emitter where particles will be created. This rule is ignored when the PSYS_PART_FOLLOW_SRC_MASK flag is set. A test in http://forums.secondlife.com/showthread.php?t=226722 indicates that the maximum value is 50.00 16
PSYS_SRC_ANGLE_BEGIN float}} Specifies a half angle, in radians, of a circular or spherical "dimple" or conic section (starting from the emitter facing) within which particles will NOT be emitted. Valid values are the same as for PSYS_SRC_ANGLE_END, though the effects are reversed accordingly. If the pattern is PSYS_SRC_PATTERN_ANGLE, the presentation is a 2D flat circular section. If PSYS_SRC_PATTERN_ANGLE_CONE or PSYS_SRC_PATTERN_ANGLE_CONE_EMPTY is used, the presentation is a 3D spherical section. Note that the value of this parameter and PSYS_SRC_ANGLE_END are internally re-ordered such that this parameter gets the smaller of the two values. 22
PSYS_SRC_ANGLE_END float}} Specifies a half angle, in radians, of a circular or spherical "dimple" or conic section (starting from the emitter facing) within which particles will NOT be emitted. Valid values are 0.0, which will result in particles being emitted in a straight line in the direction of the emitter facing, to PI, which will result in particles being emitted in a full circular or spherical arc around the emitter, not including the "dimple" or conic section defined by PSYS_SRC_ANGLE_BEGIN. If the pattern is PSYS_SRC_PATTERN_ANGLE, the presentation is a 2D flat circular section. If PSYS_SRC_PATTERN_ANGLE_CONE or PSYS_SRC_PATTERN_ANGLE_CONE_EMPTY is used, the presentation is a 3D spherical section. Note that the value of this parameter and PSYS_SRC_ANGLE_BEGIN are internally re-ordered such that this parameter gets the larger of the two values. 23
PSYS_SRC_INNERANGLE float}} DEPRECATED: Use PSYS_SRC_ANGLE_BEGIN instead. Works similar to its replacement rule, except the edge of the section is aligned with the emitter facing, rather than its center. 10
PSYS_SRC_OUTERANGLE float}} DEPRECATED: Use PSYS_SRC_ANGLE_END instead. Works similar to its replacement rule, except the edge of the section is aligned with the emitter facing, rather than the section's center. 11
PSYS_SRC_TARGET_KEY key}} Specifies the key of a target object, prim, or agent towards which the particles will change course and move. They will attempt to end up at the geometric center of the target at the end of their lifetime. Requires the PSYS_PART_TARGET_POS_MASK flag be set. caveat 4 20
Particle Appearance
PSYS_PART_START_COLOR vector}} unit vector}} specifying the {{LSLG|color}} of the particles upon emission. 1
PSYS_PART_END_COLOR vector}} unit vector}} specifying the {{LSLG|color}} the particles transition to during their lifetime. Only used if the PSYS_PART_INTERP_COLOR_MASK flag is set. 3
PSYS_PART_START_ALPHA float}} alpha}} of the particles upon emission. Valid values are in the range 0.0 to 1.0. Higher values are more opaque; lower ones are more transparent. 2
PSYS_PART_END_ALPHA float}} alpha}} the particles transition to during their lifetime. Only used if the PSYS_PART_INTERP_COLOR_MASK flag is set. Valid values are the same as PSYS_PART_START_ALPHA. (caveat 1) 4
PSYS_PART_START_SCALE vector}} scale}} or size of the particles upon emission. Valid values for each direction are 0.04 (0.03125) to 4.0, in meters. Since particles are essentially 2D sprites, the Z component of the vector is ignored and can be set to 0.0. 5
PSYS_PART_END_SCALE vector}} scale}} or size the particles transition to during their lifetime. Only used if the PSYS_PART_INTERP_SCALE_MASK flag is set. Valid values are the same as PSYS_PART_START_SCALE. 6
PSYS_SRC_TEXTURE string}} Specifies the name of a texture in the prim's inventory to use for each particle. Alternatively, you may specify an asset key UUID for a texture. 12
Particle Flow
PSYS_SRC_MAX_AGE float}} Specifies the length of time, in seconds, that the emitter will operate upon coming into view range (if the particle system is already set) or upon execution of this function (if already in view range). Upon expiration, no more particles will be emitted, except as specified above. Zero will give the particle system an infinite duration. (caveat 2) 19
PSYS_PART_MAX_AGE float}} Specifies the lifetime of each particle emitted, in seconds. Maximum is 30.0 seconds. During this time, the particle will appear, change appearance and move according to the parameters specified in the other sections, and then disappear. 7
PSYS_SRC_BURST_RATE float}} Specifies the time interval, in seconds, between "bursts" of particles being emitted. Specifying a value of 0.0 will cause the emission of particles as fast as the viewer can do so. 13
PSYS_SRC_BURST_PART_COUNT integer}} Specifies the number of particles emitted in each "burst". 15
Particle Motion
PSYS_SRC_ACCEL vector}} Specifies a directional acceleration vector applied to each particle as it is emitted, in meters per second. Valid values are 0.0 to 100.0 for each direction, as region coordinates. 8
PSYS_SRC_OMEGA vector}} llTargetOmega}}) has no effect on emitter spin. (caveat 3) 21
PSYS_SRC_BURST_SPEED_MIN float}} Specifies the minimum value of a random range of values which is selected for each particle in a burst as its initial speed upon emission, in meters per second. Note that the value of this parameter and PSYS_SRC_BURST_SPEED_MAX are internally re-ordered such that this parameter gets the smaller of the two values. 17
PSYS_SRC_BURST_SPEED_MAX float}} Specifies the maximum value of a random range of values which is selected for each particle in a burst as its initial speed upon emission, in meters per second. Note that the value of this parameter and PSYS_SRC_BURST_SPEED_MIN are internally re-ordered such that this parameter gets the larger of the two values. 18

Caveats

  1. Due to a bug (see VWR-2164) in the implementation of the particle system, any alpha change defined by setting PSYS_PART_END_ALPHA and the PSYS_PART_INTERP_COLOR_MASK flag always will add the value of PSYS_PART_END_ALPHA to the interpolated result. So if you start at 1 and go to 0.5 you expect an alpha of 0.75 when you're at half particle age. Due to the bug you'll have 1.25. As a result you can not fade in particles either as this requires you to set a high end which is added every time. So fading in from 0 to 1 actually fades from 1 to 2.
    • This is fixed in the WindLight First Look test Viewer.
  2. When using particle systems that have a non-zero emitter age (PSYS_SRC_MAX_AGE) setting, you may notice that the particle system may restart without any scripted trigger going off. This is due to a bug which causes the emitter to "reset" when any of the prim properties are updated or otherwise sent to the viewer. As a result, you may have to use a timer or a forced sleep and then clear the particle system once the age has expired. Debbie Trilling has posted a work-around here: http://forums.secondlife.com/showpost.php?p=1996465&postcount=6
  3. The spin defined by PSYS_SRC_OMEGA is relative to the region coordinate system, NOT the prim's local coordinate system.
  4. Particles moving towards a humanoid avatar, specified by PSYS_SRC_TARGET_KEY rule and setting the PSYS_PART_TARGET_POS_MASK flag, will end up at the geometric center of the avatar's bounding box which, unfortunately, make them appear to be striking the person in the groin area. If you want them to end up at another point on a target avatar, you instead have to place a target prim that is moved to the position where you wish them to end up, and use the key of that prim for the value of the PSYS_SRC_TARGET_KEY rule.
  5. The Second Life viewer uses optimizations in culling objects which are too small to see at certain distances. If your emitter is very small, and is culled due to distance, the particle system associated with it will not be rendered either.
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Examples


This example produces an effusion of glowing red spheres: <lsl>

       llParticleSystem( 
[PSYS_PART_FLAGS, PSYS_PART_WIND_MASK

Useful Snippets

Useful functions for storing/retrieving color and alpha values to/from integers:
<lsl> integer ColorAlphatoRGBA(vector color, float alpha) { return (((integer)(alpha * 255.0) & 0xFF) << 24)

Notes

  • The default particle count for the client is normally set at 4096. That is the max particle count the client will render for ALL active particle systems within view range. Good particle system design is key to avoid "spamming" everyone with your particles, and starving out other people's particle systems. As such, if you are experiencing trouble getting your particle emitter to emit as many particles as you like, it may be the victim of particle starvation. Client/viewer lag (low frame rates) can also cause this issue, as particles are a rather low priority for rendering. The best solution for this is to move to a less laggy environment relatively free of other particle systems when designing and testing your own.
  • Once particles are emitted, their direction of motion can only be affected by PSYS_SRC_ACCEL, the PSYS_PART_TARGET_POS_MASK flag, or the PSYS_PART_FOLLOW_SRC_MASK flag. As such, there is no good way to create the "swirling vortex" effect (like the one used in the viewer to indicate an object talking, begin derezzed, or when an avatar leaves the sim/grid).

See Also

Articles

•  Color in LSL
•  Translucent Color

Deep Notes

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Signature

function void llParticleSystem( list rules );