You can use a deforming plane or other flat mesh to guide the surface of a Bifröst liquid simulation, while restricting the simulation to one or more specific regions. For example, this lets you define a large ocean area with a mesh and emit particles in a smaller region. The deforming mesh lets you direct the waves artistically, while the simulation provides splashes and other fine details. Only the top layer of the liquid surface is simulated, allowing for higher resolution settings with less memory and computation time.
- Prepare the animated, deformed polygon mesh or meshes that you will use as guides.
- Although the guides should have animated deformations, the topology should not change.
- For best results, the "waves" in the guiding mesh should move in a manner that's similar to how real waves would behave. If the mesh does not deform realistically, for example if the waves are too fast or too slow, then the simulation may have artifacts or produce other unexpected results.
- For realistic ocean waves, the vertices should ideally move horizontally as well as vertically.
- The animation of the deformation should last as long as the number of frames that you want to simulate. This is a particular consideration when using cached geometry as a guide.
- With nothing selected, select . This adds a liquid simulation to the scene, but there are no particles because no emitters have been defined.
- Select the main simulation container (e.g., bifrostLiquid) or shape (e.g., liquid), as well as one or more polygon mesh objects to use as a guides
- Select
.
The selected meshes are added to the simulation as guides sharing a single guide mesh property (e.g., guideMeshProps). Additionally, Enable is activated in the Guided Simulation attribute group and Mesh is activated in the Input subgroup of the global guide properties (e.g., bifrostGuideProperties).
Note that you can add additional guide meshes later:- To share an existing guide mesh property, select it and the meshes to add, and then select .
- To use a new property, select the meshes to add as well as either the main container or shape, and then select the command.
- In the guide mesh property's attributes, activate Extrude in the Guides group. This option must always be on when the guide meshes do not form a closed volume.
- Create one or more a simple meshes such as a sphere, cube, or cylinder to define the regions in which you want to simulate. The regions should contain the volume below the guide at least to the depth you want to simulate, as well as sufficient space above for splashes. In addition, they should not extend horizontally beyond the guide meshes.
- Select the meshes that define the simulation region, as well as the bifrost shape or container object, and then select
.
The selected meshes are added to the simulation and share a single emission region property.
As with guides, you can add additional emission regions later. Select the meshes and an existing property to share it, or the meshes and the main container and shape to use a new property.
- If the region is animated, for example, to follow a moving boat, then make sure to activate Continuous Emission in the Emission attribute group of the emission region property. However, note that this option will fill in wakes.
- Optionally, adjust
Min Simulation Depth in the global guide properties. This controls the depth of the liquid in world space, and may need to be adjusted depending on the scale to which the scene was modeled.
You should see a band of liquid at the top surface of the emitters, rather than to the full depth of the emission region.
- Add any other objects to the simulation, such as colliders. See Work with Bifröst colliders.
- Play back, and adjust the settings as necessary (see Adjust a Bifrost guided simulation). Use a low resolution at first (high Master Voxel Size), and then increase the resolution once it's working satisfactorily.