Houdini 20.5 Shelf tools

Condensation shelf tool

Creates a particle simulation to mimic condensation on geometry.

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Overview

This tool sets up a particle system to simulate liquid forming, flowing, and dripping off the surface of the selected object.

The created dynamics network contains the following components:

  • Static Object from the selected geometry to allow the particles to collide with the object.

  • A particle system consisting of a POP Object and POP Solver.

  • Geometry Wrangle that applies a custom force on particles, causing them to stick to the object.

  • An emitter to continuously inject new fluid into the simulation.

  • POP Fluid node that causes the particles to behave like fluid.

Note

This tool is designed for objects whose dimensions are in the ballpark of a single unit; simulation forces may need to be adjusted if the object’s size is considerably different.

Using Condensation

  1. Create a geometry object for the condensation to form around.

  2. Click the Condensation tool on the Particle Fluids shelf tab.

  3. Select your input geometry and press Enter to confirm the selection.

The distance between fluid particles in the simulation is controlled by Particle Separation on the POP Fluid node. Consider changing this value if you want a different density of points in your fluid.

Note

Emission (handled by the source_fluid node) accounts for Particle Separation when seeding particles.

Controlling Emission

The amount of condensation largely depends on the source points, which are generated in the selected object’s network. An effective way to gauge where liquid will be injected into the simulation is to inspect the emit attribute on these source points. You can do this by creating an attribute visualizer or looking at the geometry spreadsheet. SOURCE_OUT is a convenience null that holds the final source points.

The following list outlines some basic ways to control the emission of liquid. All nodes referenced below are located inside the object-level node of your selected geometry.

To...Do this

Change the number of droplets that appear

Change the Force Total Count parameter on the Scatter SOP (create_droplet_points). This parameter’s value controls the number of droplets that form over the entire simulation.

Control when the droplets form

Change the Min Value and Max Value parameters on the Attribute Randomize node (add_emission_frame). This node randomly selects the frame to activate each droplet on, and the aforementioned parameters specify the frame range within which droplets may appear.

Control how long droplets emit liquid

Tweak fade parameters under the Timings tab of the Attribute Fade node (fade_emission).

Modify the emission size for droplets

Change the Distance Threshold on the Attribute Transfer node (transfer_emission).

Change where the droplets appear

Modify the Global Seed parameter on the Scatter SOP (create_droplet_points).

Choose exactly where condensation will appear on your object

Replace the create_droplet_points, add_emission_frame, and fade_emission nodes with your own manually created points and wire them into the DROPLETS_OUT node. You must also create an attribute called emit on those points that will be picked up by the Attribute Transfer node (transfer_emission).

Note

As far as POP Fluid DOP is concerned, each simulation particle represents an equally massive chunk of liquid. This is very different from a FLIP simulation, where particles signal the presence, but not amount, of fluid. Placing a large number of particles in close proximity is akin to compressing a liquid, and will result in particles exploding outwards. Great care must be taken should you choose to modify sourcing parameters in the DOP network.

Changing the behavior of the condensation

To...Do this

Make the liquid drip off the object quicker

Lower the Strength Multiplier parameter on the Geometry Wrangle (adhesion_force). This parameter controls how strong the force is that holds the particles to the geometry. If this value is 0, the liquid will not follow the surface to the lowest point before dripping off. It will simply fall down as gravity pulls it.

Control how slowly the liquid flows over the object

The Friction parameter on the POP Object controls how the liquid moves along the surface of the object. This can be modified along with the Strength Multiplier parameter on the Geometry Wrangle node (adhesion_force) to control the behavior of the fluid along the surface of the object.

Shelf tools

Using the shelf

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    How to change the look of the shelf, change and rearrange its contents, and create your own shelf tools.

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