Houdini 13.0 Nodes

interface version 1

A more convenient alternative for the original Source POP.

This operator is a wrapper around the original Source POP, providing the following additional/alternative features:

  • Birth rates have multiplier values (for easier gradual emission adjustment)

  • A global birth rate multiplier is also provided (to reduce overall particle count, for faster previews, etc.)

  • Useful presets for activations and birth rates

  • Lifespan variance is specified using min/max values

  • Restrictive default settings for attribute inheritance (not inheriting all attributes by default, just velocity and up vector)

Parameters

(Only the additional parameters are described here. See the Source POP documentation for the regular node parameters.)

POP Network

Name of the POP network that contains this node. The path “..” is usually fine – this parameter needs to be set only if the Source node is within a subnet in the POP network.

The container POP network path is needed for certain operations (e.g. creating a global rate multiplier) or expressions (e.g. preset for first frame-only emission).

Create & Link to Popnet Global Rate

This button will create a “Global Rate Mult %” parameter on the parent POP network container and links this parameter to the same parameter on the Source SOP.

Tip

By linking all Sources to the container this way, the total amount of processed particles can be easily controlled. (The fastest way is to link one Source, then copy the ch() expression from that node to all the other Sources.)

Source (tab)

No additional features.

Birth (tab)
Global Rate Mult %

An overall emission rate multiplier, affecting all emission types. All emission rates get multiplied with this value.

Tip

(todo: tip about wedged particles workflow)

Impulse Activation

Same as the original Source POP parameter.

There is a menu preset that provides emission on the first frame of the particle simulation (also takes preroll into account).

Impulse Birth Rate

Same as the original Source POP parameter. Note that this is a per-frame emission amount.

Impulse Mult %

A multiplier on the impulse birth rate. Useful to add gradual changes to emission rates (e.g. animation) without animating the rate parameter itself.

Constant Activation

See Impulse Activation above (same presets provided).

Constant Birth Rate

Same as the original Source POP parameter. Note that this is a per-second emission amount (i.e. per-frame values should be multiplied by $FPS to get the expected result).

Constant Mult %

See Impulse Mult % above.

Life Expectancy Type

The way of specifying particle lifespan settings.

Min/max

Lifespan values will be chosen at random from a min/max value range.

Life +- variance

Lifespans will be generated by randomly picking numbers, centered at the expectancy value with the given variance (default Houdini behaviour).

Life Min, Max

Lifespan range of the emitted particles (per-second).

These are min/max settings, meaning that all particles will live at least as long as Life Min, but no particle will live longer than Life Max.

Life Expectancy, Life Variance

Lifespan settings for life/variance mode. (This is the original emitter behaviour.)

Attributes (tab)

No additional features.

Add Attributes (tab)

No additional features.

Warning

LIMITATION: Most of the local variables specific to the original Source POP are not available in the node parameter fields (most notably $NPT which refers to the point count of the emission source geometry).

The exceptions (where all local variables are available) are the emission rate and originindex parameter fields. (Due to technical issues, these can’t display their proper numeric values, but all variables work properly.)

(It’s possible to fix this behaviour for all params, but it would turn node internals ugly. As usual, user feedback will decide this question: btw, that means you too.)

Release Notes

interface version 1 —

2013-05-25

  • Replaced some preset double-quotes to single-quotes to avoid a recurring Houdini bug that generates large amount of backslash characters in assets over time.

2013-05-20

  • Added oversample parameter (linked to container popnet by default). Currently it used for emission amount compensation (i.e. the source emits the same amount of particles per frame, regardless of POP oversampling settings.)

2013-05-19

  • Minor UI changes (activation values of 0 disable related controls)

2013-05-01

  • Added birthtime, relbirthtime and phase as default inheritable attribute (subframe particle accuracy support)

2013-01-22

  • Minor UI fixes and changes

  • More restrictive default settings for attribute inheritance

  • Original Source POP variables (e.g. $NPT) now work (but only in the Birth Rate and originindex fields right now)

  • Now supports both lifespan (expectancy) modes (min/max and lifespan/variance)

2013-01-21

First version.