Stream
particle node
Emit particles from areas where streams of particles mix.
See also: Location, Source, Split
This operator divides space into equal-sized partitions, and then emits particles from any partition where the density of particles from one or more streams is above a per-stream threshold. This can be used, for example, to generate sparks where two particle beams cross.
Smaller values for the Division Size parameter gives more partitions and a higher resolution; however, it also increases cooking time. Keep in mind that if you decrease the size of the partitions, you probably also want to decrease the thresholds.
Parameters
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Activation |
Turns this node on and off. A value of 0 means off, any other value means on. This is useful to control the effect of this node with an expression . |
Source
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Birth Position |
Where in the partition to emit new particles when the density is above the threshold. |
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Division Size |
Size of the partitions. |
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Offset of Grid |
Distance to offset the partition grid from the default. |
Enable
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Enable Stream n |
Use stream n. |
Group
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Group n |
Subset of the input particles to use as stream n. |
Threshold
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Threshold n |
Number of stream <n> particles required in a partition to emit a new particle. |
Kill
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Kill original particle n |
When a new particle is emitted, kill the source particles from this stream in the partition. |
Birth
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Birth Probability |
How many particles to emit in each partition. |
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Birth Group |
Name of a group to put the new points into. |
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Preserve Group |
If the Birth group already exists, append the new particles to the group instead of replacing its contents. |
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Life Expectancy |
How long the particle will live (in seconds). |
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Life Variance |
Particles will live the number of seconds in Life expectancy, plus or minus this number of seconds. Use 0 for no variance. |
Attributes
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Initial Velocity |
How to set the initial velocity of the emitted particles.
Note
Acceleration is inherited independently, if applicable. |
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Inherit Velocity |
(When Initial velocity is Use inherited velocity or Add to inherited velocity) The proportion of the inherited velocity to use. Use |
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Velocity |
Set or add to velocity attribute. |
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Variance |
Variance to velocity set above. The node will add +/- from 0 to this number along each axis to the Velocity parameter. |
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Ellipsoid Distribution |
By default, the variance (if any) is distributed in a box, the size of which is determined by the Variance parameter. When this option is on, the variance is distributed in an ellipsoid instead. |
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Origin Index |
Value for the origin attribute. |
Local variables
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DENSITY |
Total number of particles from enabled streams contained in the partition. |
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THRESH |
Sum of all enabled stream thresholds. |
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TIMEINC |
Time increment for this cook. |
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TX, TY, TZ |
Birth Position. |
Example files
SparksStream
$HFS/houdini/help/examples/nodes/pop/stream/SparksStream.cmd
This network utilizes a Stream POP to birth new particles based on the particle density per unit division of space where to particle streams flow and collide. Thelower the threshold, the less particles needed to trigger new particle birthing by the Stream POP.
Some particles are birthed from a grid and are then subjected to a vortex force.The drag is needed to prevent the blue particles from continually expanding while keeping them moving in a circle.
After about 140 frames, the ring should be fully formed and now a spray of red particles start shooting off from the center of the ring (birthed by a circle source geometry).
These two streams are fed into the Stream POP. The Stream POP will birth particles where the two streams intersect. It does this by spatially subdividing the area where the particles flow, and then measuring the particle number within the.
Usages in other examples
| Example name | Example for |
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