The selection marker

A box around the selected piece, shown whenever something is selected — including when no transform is enabled, which is the whole reason it exists.

Why an outline was not enough

There is a HighlightLayer too, and for a long time there was only that. It had never worked: both kinds of body hand you a TransformNode at the top, the layer takes meshes, and the call that fed it one was wrapped in a catch. So "the piece you are about to move" was communicated by a property panel and nothing else, twice reported and once wrongly believed fixed.

Even working, a glow is the wrong signal here. It says which mesh and nothing about how big the thing is, which in an arrangement editor is most of what you want to know. A box answers that and recolours nothing.

There were three axis rods through the origin as well, and they are gone: with a manipulator present they duplicated its shafts, and without one they were more clutter than information.

Quiet, but not invisible

The first version used CreateLines for the axes and a wireframe material for the box. Both render — measured: four meshes, visible, enabled, in the active list — and both are effectively one pixel wide, because WebGL has no line width. On a phone that is nothing at all: "I don't see selection feedback so I need to turn on transformation to get any selection feedback."

So the box is drawn by enableEdgesRendering, which emits its twelve edges as camera-facing quads at a width in PIXELS. A wireframe material cannot do this job twice over: its lines are one pixel wide at every distance, and it draws the triangulation — a diagonal across every face, which is exactly the "triangles splitting the faces" that made the box distracting. Edges skip them by design.

The mesh itself is fully transparent. It is still rendered, which is what gives the edge renderer something to hang off; it simply contributes no pixels of its own.

It marks the selection; it is not a control, and anything that LOOKS grabbable but is not is worse than nothing.