Brush geometry kernel - first-class concave brushes and robust CSG #38

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Rbanh · 2026-06-06T13:42:16-04:00

Rbanh commented

2026-06-06 13:42:16 -04:00

Summary

Refactor brush geometry around an authored-vs-compiled architecture so Blacksite can support first-class concave authored brushes and robust CSG beyond the Jackdaw-inspired MVP.

Why

M1 brush work intentionally keeps the persisted brush contract convex and uses MVP/bounds-oriented operations for blockout speed. That is enough for milestone QA, but it is not the final architecture for production-grade CSG, concave face authoring, material-preserving cuts, collision generation, or stable face/edge editing.

Proposed architecture

Add an authored brush representation that can store simple concave planar faces while rejecting self-intersections, non-planar faces, zero-area faces, and ambiguous duplicate vertices.
Add a compiled brush representation used by rendering, picking, collision, hydration, save validation, and diagnostics.
Compile authored concave faces into triangulated or convex-decomposed output with stable mapping back to authored face IDs.
Replace MVP bounds-based CSG with geometry-kernel operations that produce validated compiled output and authoring data.
Preserve material refs, texture refs, UV transforms, smoothing groups, and stable face IDs where topology permits.
Keep generated runtime mesh/collider data out of scene save files.

Acceptance criteria

Authored simple concave brush faces can be saved, loaded, selected, edited, and hydrated.
Self-intersecting or non-planar faces are blocked with actionable diagnostics.
Rendering and collision consume compiled brush geometry, not ad hoc generated meshes.
Subtract/intersect/merge operate on arbitrary supported brush geometry, not only convex/bounds MVP cases.
CSG outputs preserve material/UV data on surviving or split faces where matchable.
Brush picking maps compiled triangles back to authored brush faces/elements.
Golden fixture tests cover concave face triangulation, convex decomposition, cube subtract cube, concave subtract, non-overlap, degenerates, and material/UV preservation.

Relationship to M1

M1 should not wait on this. For the current milestone, concave draw input should be normalized into a composition of convex brush pieces, and self-intersecting input should remain blocked.

## Summary Refactor brush geometry around an authored-vs-compiled architecture so Blacksite can support first-class concave authored brushes and robust CSG beyond the Jackdaw-inspired MVP. ## Why M1 brush work intentionally keeps the persisted brush contract convex and uses MVP/bounds-oriented operations for blockout speed. That is enough for milestone QA, but it is not the final architecture for production-grade CSG, concave face authoring, material-preserving cuts, collision generation, or stable face/edge editing. ## Proposed architecture - Add an authored brush representation that can store simple concave planar faces while rejecting self-intersections, non-planar faces, zero-area faces, and ambiguous duplicate vertices. - Add a compiled brush representation used by rendering, picking, collision, hydration, save validation, and diagnostics. - Compile authored concave faces into triangulated or convex-decomposed output with stable mapping back to authored face IDs. - Replace MVP bounds-based CSG with geometry-kernel operations that produce validated compiled output and authoring data. - Preserve material refs, texture refs, UV transforms, smoothing groups, and stable face IDs where topology permits. - Keep generated runtime mesh/collider data out of scene save files. ## Acceptance criteria - [ ] Authored simple concave brush faces can be saved, loaded, selected, edited, and hydrated. - [ ] Self-intersecting or non-planar faces are blocked with actionable diagnostics. - [ ] Rendering and collision consume compiled brush geometry, not ad hoc generated meshes. - [ ] Subtract/intersect/merge operate on arbitrary supported brush geometry, not only convex/bounds MVP cases. - [ ] CSG outputs preserve material/UV data on surviving or split faces where matchable. - [ ] Brush picking maps compiled triangles back to authored brush faces/elements. - [ ] Golden fixture tests cover concave face triangulation, convex decomposition, cube subtract cube, concave subtract, non-overlap, degenerates, and material/UV preservation. ## Relationship to M1 M1 should not wait on this. For the current milestone, concave draw input should be normalized into a composition of convex brush pieces, and self-intersecting input should remain blocked.

Rbanh added this to the Post-Jackdaw - Brush geometry kernel and first-class CSG milestone 2026-06-06 13:42:16 -04:00

Rbanh added the

type:feature

area:brushes

labels 2026-06-06 13:42:16 -04:00

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Reference: Falling-Metal-Interactive/Blacksite#38