Advanced mode

Overlays

Four viewport overlays that draw the data behind the mesh. All off by default, because an overlay you did not ask for is clutter — and all worth turning on the moment something is not behaving.

Boundary edges

Highlights every edge belonging to only one face, drawn in the accent colour. These are the open edges of your mesh.

Worth turning on when:

A Conway chain refuses, saying the input is not manifold. This shows you exactly where.
Boundary handling is producing something unexpected and you want to know which faces count as boundary faces.
A mesh looks closed and is not. An imported model with a hole somewhere unhelpful is extremely common, and this finds it in a second.

Face orientation

Draws an arrow per face showing the direction of its first corner — which is what “default rotation” follows in tessellation.

This is the diagnostic for the most confusing class of tessellation artifact: copies correctly placed but inconsistently rotated. If the arrows are scattered where the geometry looks regular, the face winding is inconsistent, and Rotate faces is the fix. If the arrows are consistent and the copies still are not, the problem is somewhere else entirely and you have saved yourself an hour.

Field heatmap

Draws any named attribute as a colour overlay on the mesh, with a small screen-space legend showing the value range.

Attribute: Which field to draw. Type the name of any float attribute or vertex group on the object.
Legend: Shows the numeric range being mapped. Turn it off once you know the range and want the viewport back.

This is the most useful overlay in the set, because it closes the loop on field authoring. Without it, tuning a field means generating it, applying it to something, looking at the result, and inferring backwards. With it, you can watch the field itself change as you drag the contrast slider.

The workflow this enables

Turn on the heatmap. Set it to your field's attribute name. Now adjust the generator and the whole modifier chain — remap, contrast, blur, quantise — watching the field directly. When it looks right, then drive something with it. This is roughly ten times faster than the alternative.

Planarity heatmap

Per-face planarity deviation as colour, with a legend. Green is within tolerance, red is not.

Run Analyse planarity first — the overlay draws the attribute that analysis writes. Use it before planarising to find out whether you have a problem, and after to confirm you fixed it. On a doubly-curved surface, expect the residual red to cluster where curvature is strongest, which is exactly where a fabricator will tell you the panels are expensive.

Cost and behaviour

Overlays are drawn with the GPU module and are designed not to become the thing that slows you down:

Frustum culled. Geometry outside the view is not drawn.
Vertex budget capped. Very dense meshes are decimated for display rather than drawn in full.
Rebuilt only on change. The batch is regenerated when the underlying data or the view changes, not every redraw.
Not drawn when the Rhea tab is hidden. Switch to another sidebar tab and the overlays stop costing anything.

They are still not free on a multi-million-vertex mesh. If the viewport is sluggish, the overlays are worth checking before anything else.

Defaults

All four are off by default, per object. You can set your preferred defaults in Rhea's preferences if you would rather always have, say, boundary edges on.