Houdini 20.0 Nodes Geometry nodes

Pyro Spawn Sources geometry node

Creates spawn points for sourcing pyro simulations with packed sets.

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Since 19.5

The Pyro Spawn Sources SOP creates spawn points for sourcing pyro simulations using packed source sets. These points identify the relevant packed sets and store some basic animation data, such as when the source is to engage, how quickly it should play back, and how frequently it should repeat. Additionally, this operator facilitates some basic source rule overrides to adjust rules that come with the packed set.

The spawn points can be modified downstream to adjust (or randomize) their properties, which are stored on point attributes; for example, you can use Attribute Adjust Float to randomize the startframe values, causing the different sources to engage on different frames. Key point attributes of spawn points are listed below.


Name of the packed source set that we want to instance.


Location of the instance in world space.


Orientation of the instance in world space.


The local pivot point for this instance.


The instance is activated on this playbar frame.


If greater than startframe, the instance will not be active beyond this playbar frame.


If this value is no smaller than 1, then the source sequence will loop. The looping sequence starts at startframe and is looplength frames in length.


When the instance first engages (on startframe), it starts sourcing at this offset within the packed source set’s frame range.


Length of the subsequence to use from the packed set’s full frame range. For example, if startoffset is 0 and offsetlength is 5, then only offsets 0-5 will be used for sourcing. If offsetlength is smaller than 0, then all frames from the packed set can be used.


Playback speed of the source once it engages. For instance, if startoffset is 1 and sourcespeed is 2, then offset 1 of the packed set will be sourced when it first engages, followed by offsets 3, 5, ... on subsequent frames. This speed can be negative.


The Pyro Source Instance operator can take spawn points and generate instance points from them when they activate. The instance points are injected by the Pyro Solver to source the packed sets into a simulation.


Input Points

Input points to turn into spawn points. If no input is provided, a spawn point will be generated at the origin.y


Spawn Points

Spawn points that can be turned into instance points for the Pyro Solver by the Pyro Source Instance SOP.



When specified, only the subset of the input geometry corresponding to this group is modified.

Source Name

Spawn points will be for the packed source set of this name. This string is put into the name attribute.

Start Frame

The source is first engaged on this frame. This value is stored on the startframe attribute.

Stop Frame

If turned on, the source will not be active after this frame. This value is stored on the endframe attribute.

Start Offset

When the instance first engages, it starts sourcing at this offset within the packed source set’s frame range. This value is stored on the startoffset attribute.

End Offset

When turned on, only offsets of the packed source set in the range between Start Offset and End Offset will be sourced. This value affects the offsetlength attribute.

Source Speed

Playback speed of the source once it engages. Source Speed can be set negative, in which case the packed set will animate in reverse. This value is saved in the sourcespeed attribute.

Loop Length

If turned on, a sequence of this length will loop starting at Start Frame. For example, if you start sourcing on frame 6, and Loop Length is 4, then frames 6, 10, 14, ... will all apply the same sources. This value is saved in the looplength attribute.

Rule Overrides

The spawn points can make adjustments to the packed set’s merging rules using these Rule Overrides. For example, you can turn off a rule by specifying its Target Field and setting the Activation Multiplier to 0.

Target Field

This parameter is used to identify which rules should be adjusted: any rule that applies to this Target Field will get the override.


Specifies which property of the rule to override. The value of this property for the relevant rule is scaled by Multiplier.


The applied scale factor. The selected Property of any rule that affects the Target Field will be multiplied by the value of this parameter.

See also

Geometry nodes