# Brush Authoring

Brushes are persisted blockout geometry stored as `ActorKind::Brush + BrushDesc`.

## MVP Scope

- `BrushDesc::default()` creates an additive cube brush.
- Each face stores a stable ID, plane, vertices, optional material/texture refs, UV offset/scale/rotation, and smoothing group.
- Hydration builds generated mesh children from active brush components and strips those children before scene save.
- Brush actors validate separately from primitives and imported/static mesh actors.
- The Actor Inspector Add Component shelf can add a **Brush** component. The Brush card exposes kind, face count, shadow flags, and cube reset.
- Draw Brush mode (`B`, toolbar pencil, or command `brush.draw`) creates additive prism brushes from snapped floor points. LMB places points, Backspace removes the last point, Enter commits through undo history, and Esc/right-click cancels without scene mutation.

## Element Modes

With a brush actor selected, `1`/`2`/`3`/`4` enter vertex, edge, face, and clip modes. Element modes show viewport overlays for the selected brush, route LMB to element picking, support Shift+LMB multi-select, and display a `Brush: <mode>` badge. `Esc` returns to object mode.

The current slice selects elements and visualizes handles; mutating vertices/faces and committing drag edits through history is the next implementation layer.

## Current Limits

- Only convex authored faces are supported by the mesh builder.
- Subtractive brushes are stored as markers but are not evaluated as CSG.
- Face, edge, vertex, clipping, and primitive brush creation tools are future roadmap work.