Reference/Release Notes/2.91/Physics

Rigid Bodies

  • Support for "Compound Shape" collisions (820ca419e0).
  • You now can combine multiple primitive shapes into a concave shape. For instance, to a chain link collision shape you can use multiple wire edge child objects:
Chain link compound shapes.png
  • Doing it like this makes the simulation run a lot faster than if using the "mesh" collision shape. It is also in most cases a lot more stable.


  • Improved obstacle handling:
    • Advanced obstacle-liquid interaction (UI toggle "Fractional Obstacles") has been improved
    • Particles now flow more smoothly over inclined obstacles
    • For even finer control, there is a new option "Obstacle Distance" which defines the distance that liquid will maintain towards any obstacle.
Old simulation behavior (2.90): Some particles stick to obstacles
New simulation behavior (2.91): More fluid flow along obstacles
  • OpenVDB cache:
    • In .vdb format, liquid simulations can now be saved with Full (32 bit), Half (16 bit) or Mini (mix of 8 bit and 16 bit) precision (2ec07dfa18, 3d1b5e35bd)
    • Especially scenes with large amounts of liquid particles benefit from smaller cache file sizes as viewport performance increases significantly
    • E.g. beach scene from above (~300.000 liquid particles): Before 4.1 GB, now (Mini format) 1.26 GB
  • Improved "Viewport Display" options:
    • Note: This feature is aimed at developers and when a deeper inspection of the simulation is required.
    • It is now possible to visualize liquid simulations grids (before only smoke).
    • Vector display options have been improved: Velocities and forces can now be viewed per axis (MAC visualization).
    • An option to display gridlines for the underlying simulation grid has been added.
    • Cell coloring options have been added: Obstacle, fluid and empty cells can be identified in the underlying grid.
    • In-depth report: Liquid Simulation Display Options (f137022f99)
  • Visualization of a 2D slice of the fluid level-set representation in a liquid simulation. (Display Thickness used: 0.02)
  • MAC Grid visualization for a 2D slice of the velocity vector field in a liquid simulation.