Blacksite/docs/editor/brushes.md

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.
• The Brush card runs shared validation and reports invalid faces inline. Fatal geometry errors prevent hydration; warnings call out authoring issues that can still render. Reset Cube Brush is the MVP repair path.
• Scene save runs the same fatal brush validation and blocks writing unrecoverable invalid brush geometry.
• Window → Brush Diagnostics lists all brush actors, surfaces validation counts/messages, can select the affected brush, and provides an undoable Reset Cube repair for invalid brushes.
• 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.

Vertex, edge, and face selections can be dragged on the viewport floor plane. The editor moves matching duplicated corner vertices across all brush faces so simple cube/prism brushes stay welded, recomputes face planes, validates the result, and commits one undoable brush edit when the drag releases. Invalid drag results are rejected with operator status text and reverted to the pre-drag brush.

Clip mode is a bounds-based MVP for cuboid/prism blockout. Select one face in Clip mode to preview the half-brush result along that face's dominant normal axis; the magenta wireframe shows the pending trimmed bounds. Enter commits the clip through history and Esc returns to Object mode.

When one or more faces are selected in Face mode, the Brush inspector shows selected-face controls for UV offset, UV scale, UV rotation, material ref, and texture ref. Material and texture rows use Asset Browser-aware picker controls with clear, locate, browse, and compatible drag/drop assignment. These fields edit the persisted BrushFaceDesc data through undoable brush updates. Face refs cache loadable source paths when available; hydration groups faces by material/texture path and spawns separate generated mesh children for those batches.

Boolean Operations

The command palette exposes brush.subtract, brush.intersect, and brush.merge_convex for selected brush actors. The current implementation is a conservative bounds-based MVP intended for cuboid/prism blockout brushes:

• Intersect replaces the primary selected brush with the overlapping bounds of all selected brushes and deletes the other selected brushes.
• Convex Merge replaces the primary selected brush with the bounding cuboid union and deletes the other selected brushes.
• Subtract clips the primary selected brush to the largest remaining axis-aligned slab after subtracting the second selected brush; the cutter remains in the scene.

These operations validate selected brushes before previewing results and validate the generated result before any scene mutation. A cyan wireframe preview shows the pending bounds result; Enter commits and Esc cancels. Failed operations report status text and leave the scene untouched. Successful operations commit through history but are not full arbitrary-face CSG yet. Full convex clipping, multi-output subtraction, and material-preserving face matching remain future work.

Current Limits

• Only convex authored faces are supported by the mesh builder.
• Brush diagnostics currently cover face validity, plane normals, inverted face normals, finite vertices, duplicate vertices, degenerate area, open/non-manifold edges, and UV scale warnings.
• Subtractive brush markers are stored but not automatically evaluated.
• Arbitrary plane clipping, split-into-two output, and arbitrary-face CSG remain future roadmap work.
• Imported source-material subasset refs persist for future material-preserving CSG, but only face refs with loadable source paths can drive brush material hydration today.