Houdini 20.5 Shelf tools

Guided Ocean Layer shelf tool

Creates a FLIP fluid simulation that simulates a thin layer of the ocean surface.

On this page

Overview

This tool creates a guided FLIP simulation of a thin particle layer on top of an ocean surface. The particles are initialized with ocean velocities. The ocean surface at a specified depth acts as a collision layer underneath the particles, allowing the particles to closely match the ocean waves. A boundary layer of particles suppresses reflections at the edge of the tank, contributes ocean velocities back to the simulation, and maintains the water volume level to match the ocean. The FLIP Simulation uses a guiding volume approach to maintain ocean velocities through the simulation.

The thickness of the thin layer will determine how closely the simulation matches the underlying ocean surface. The thickness will also determine how well the simulation can capture motion below the surface such as wakes and vortices.

The Guided Ocean Layer can be a static simulation or can follow a moving object through the ocean.

The Ocean Spectrum node allows you to shape the initial frame of your simulated ocean, and Ocean Source controls the outputs.

Tip

For more information, see the differences between ocean tank types help page.

Using Guided Ocean Layer

  1. Click the Guided Ocean Layer tool on the Oceans tab to create a tank.

  2. Select an animated object to follow and press Enter to confirm your selection. If no object is selected, you will be prompted to place a static tank.

Note

The layer for free fluid particles between the ocean surface and the guiding volume is controlled by the Layer Size parameter in the Ocean Source SOP.

For specific parameter information, see the Ocean Source help page.

Changing the look of your ocean

To...Do this

Set the height of the wave

Navigate to the Ocean Spectrum node and adjust the Wave Scale parameter on the Wave Amplitude tab.

This value is multiplied by the Speed parameter on the Wind tab.

Set the direction of the waves

Navigate to the Ocean Spectrum node and adjust the Directional Bias parameter on the Wind tab.

This controls how many frequencies are moving in the same direction as the wind. Increasing this value will cause more frequencies to travel in the same direction, which is useful for creating shoreline effects.

You can also try increasing the Directional Movement parameter. This will dampen the waves moving in the opposite direction of the wind, leaving only the ones moving in the same direction.

Control the height of the peak

Navigate to the Ocean Spectrum node and adjust the Chop parameter on the Wind tab.

Increasing this parameter creates sharp peaks on waves. However, if this value is too high waves, may invert on themselves.

Add more detail to your ocean

Increase the Resolution Exponent parameter on the Ocean Spectrum node.

Note

The Resolution Exponent parameter will not only determine the quality of your ocean, but also the size of the texture maps that you will eventually write out.

Create a large ocean

Use the Large Ocean shelf tool.

Understanding the network of nodes

There are three important layers to focus on when creating your ocean. First create the ocean, next add whitewater, and finally add specularity for the whitewater.

Tip

Disable all whitewater nodes at the OBJ level while you work on your ocean, then disable the ocean nodes while you work on your whitewater.

The first set of nodes control the ocean itself.

  1. fluidtank_initial controls the first frame of your simulation. This is where you can shape the initial frame of your tank with Ocean Spectrum and control the outputs with Ocean Source. This includes the size of your tank, the depth of the water etc.

  2. AutoDopNetwork controls the simulation of your tank. This is where you will find the FLIP Object and FLIP Solver. The FLIP simulation will contain Volume Source DOPs to sink and source the boundary layer particles, and a Gas Guiding Volume DOP to add ocean velocities to the simulation. Note, the Beach Tank shelf tool uses POP Advect By Volumes to inject ocean velocities.

  3. fluidtank_fluid is the result of #1 and #2 combined, and is where the results are rendered. After the simulation is done, this node collects the fluid particles, sets up a material, creates some nodes for surfacing to finish the effect.

  4. fluidtank_interior is also used for rendering, and for creating the volumetric effect that one of the shaders applies to the interior of the fluid. It controls the volume beneath the surface, such as how cloudy or murky the water will appear.

The next set of nodes are to control the whitewater.

Note

To add whitewater to your simulation, use the Whitewater tool on the Oceans shelf.

  1. whitewater_source is where the spray and foam is coming from.

  2. whitewater_sim is where the whitewater simulated. This is where you can modify the animation.

  3. import_whitewater is the result of #1 and #2 combined.

For more information see How to animate a wave tank with whitewater.

Note

If you build a completely procedural ocean (using the the Large Ocean or Small Ocean shelf tools for example), the Ocean Foam SOP is used.

Understanding the extended ocean surface nodes

The Guided Ocean Layer and Ocean Flat Tank tools also create a network for rendering an “extended” fluid surface that can stretch to the horizon and be rendered with ocean displacement to provide a seamless integration between a FLIP simulation and the surrounding source ocean.

  1. The Particle Fluid Surface node (called particlefluidsurface1) creates the extended FLIP mesh. The settings on the Flattening tab of this node will flatten the fluid simulation near the edges of the simulation area, and extrude the edges of the polygonal mesh outwards to form an extended flat surface. This flat area surrounding the simulation is then rendered with ocean displacement.

  2. The two Particle Fluid Mask nodes (called particlefluidmask1 and hifrequency_mask) will create masks on the input ocean spectra that limit the render-time ocean displacement to specified areas of the simulation, usually where there is little velocity, vorticity, or splash height in the fluid. These nodes also blend in ocean displacement around the edges of the simulation bounding box to match the flattening applied while surfacing. The hifrequency_mask node additionally filters the incoming ocean spectra to remove all but the highest-frequency waves, usually so these can be applied to the simulated FLIP mesh and allow it to better integrate with the surrounding ocean.

  3. The surface_preview node is a fast preview of the FLIP simulation that then samples the created mask to allow visualization of the ocean contribution using a viewport visualizer on the mask attribute. The oceanevaluate1 node applies ocean displacements to that preview based on the calculated masks.

  4. The split_spectra_masks node will separate out the static ocean spectra from the time-dependent masks created by the masking nodes. They are cached to two different sets of files to take advantage of the Ocean Surface material’s ability to have separate spectra and mask inputs.

Tips for improving the look of your water

  • The defaults for the tank will create a low res simulation, which makes it easy to animate. However, to create a nice looking render, you will need to change some of the defaults. For example, you will need to increase the number of particles in your scene. Decreasing the Particle Separation parameter to about 0.03 will create a simulation with approximately 30 million particles.

  • Add an environment light to your scene. Water reflects and refracts a lot of the environment around it, so having an environment map in your scene will significantly improve the look.

    Tip

    In your Environment Map parameter, navigate to the HFS/houdini/pic/ folder and choose the sky file DOSCH_SKIESV2_${F2}SN_lowres.rat.

See also

Shelf tools

Using the shelf

  • Customize the shelf

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

Technical