Simple mode

Symmetry and animation

Two features that seem unrelated and are not: both exist because Rhea's controls are real Blender properties evaluated inside the modifier stack, and both required doing something slightly unusual to make them behave the way you would expect.

Symmetry

Toggle X, Y or Z in the Effects section and Rhea adds a mirror modifier below the effect stack. This ordering is the whole point.

  Rhea Symmetry     ← mirror first
  Rhea Density
  Rhea Engine 1     ← effects see the whole mirrored mesh
  Rhea Engine 2

  ▸ pattern runs continuously across the seam

Put the mirror above the effects instead, the way you would normally stack modifiers, and you get two separate patterned halves meeting at a visible join. Put it below and the effect sees one continuous surface, so cells straddle the centreline and struts cross it properly.

X / Y / Z: Which axes to mirror on. They combine — X and Y together give four-fold symmetry.
Bisect: Cuts the source geometry at the mirror plane before mirroring, so anything crossing the plane does not produce a doubled overlap. Turn this on if your base mesh is not already exactly half.
Merge: Welds vertices that land on the mirror plane. Leave on for watertight results; turn off if the weld is pulling geometry that should stay separate.

Symmetry is also a performance tool

A mirrored half evaluates one field, one pattern, one solve — then duplicates the geometry. For a symmetric design this is close to half the cost of building the whole thing.

Clearing it

Clear symmetry removes the modifier. It does not apply it, so your mesh returns to being one half. If you want the mirrored geometry to become real, apply the effect stack instead.

Animation

Every live control is a real property, so you can right-click it and Insert Keyframe, or drive it from anything Blender can drive things with. Thickness, height, twist, taper, coverage, seed — all of them.

01
Set the start
Go to frame 1, set Thickness to something small, right-click it, Insert Keyframe.
02
Set the end
Go to frame 120, raise it, keyframe again.
03
Play
The struts thicken over four seconds. Nothing was baked; the mesh is being rebuilt every frame from the changing value.

Why this needed doing on purpose

A Geometry Nodes modifier does not read add-on properties by itself. Rhea installs a frame-change handler that pushes each control's current value into the modifier before the frame draws. Without it, a keyframed Thickness would animate in the panel and do nothing to the mesh — which is the behaviour you get from most add-ons that expose controls this way.

Animating the base, not the controls

The other kind of animation, and often the better one: leave the effect settings alone and animate the surface underneath. Deform the base with a lattice, a shape key, an armature or a simulation, and the pattern follows it — struts stretch and compress, tessellated copies rotate to stay on their faces.

This works because live effects evaluate after whatever is above them in the stack, so they see the deformed mesh, not the rest pose. An animated tessellation over five thousand faces rebuilds in under a tenth of a second, which is what makes it scrubbable rather than a render-only trick.

Animating the seed

Keyframing Seed produces a hard cut between two arrangements rather than a transition, because seeds are not a continuous space. Use it deliberately — a stepped seed on a fast cycle reads as flicker or churn, which is occasionally exactly what you want, and never something you get by accident.

Rendering animated results

Live effects render exactly as they preview. There is no bake step and nothing to remember before hitting render.
Rhea never rebuilds applied stack items during a render, so a render cannot be interrupted by a background rebuild.
Check the frame range in the viewport before committing to a render. A stack that scrubs at ten frames a second is fine; one that takes two seconds a frame will take hours you did not budget for.
If a specific frame is all you need, apply the stack on that frame and render plain geometry. It is faster and it removes every variable.

Baking motion for export

Game engines and most interchange formats will not carry a Rhea modifier. For those, apply the stack per frame or use Blender's own Alembic or mesh-sequence export, which evaluates modifiers as it writes. The growth module has its own Bake to frames mode for the same reason — a solver's state cannot be reconstructed from a property value alone.