111 3D: Checking and repairing mesh orientation

9.3

Racket

111 3D: Checking and repairing mesh orientation🔗ℹ

struct
(struct mesh3d-duplicate-triangle ( first-triangle-index
duplicate-triangle-index
winding)
    #:transparent)
  first-triangle-index : exact-nonnegative-integer?
  duplicate-triangle-index : exact-nonnegative-integer?
  winding : (or/c 'same 'reversed)

Records a later triangle that has the same three indexed vertices as an earlier one, independent of cyclic rotation.

struct
(struct mesh3d-analysis ( vertex-count
triangle-count
edge-count
degenerate-triangles
duplicate-triangles
boundary-edges
boundary-loops
nonmanifold-edges
inconsistent-winding-edges
connected-components
isolated-vertices
signed-component-volumes
watertight?
orientable?
consistently-wound?)
    #:transparent)
  vertex-count : exact-nonnegative-integer?
  triangle-count : exact-nonnegative-integer?
  edge-count : exact-nonnegative-integer?
  degenerate-triangles : vector?
  duplicate-triangles : vector?
  boundary-edges : vector?
  boundary-loops : vector?
  nonmanifold-edges : vector?
  inconsistent-winding-edges : vector?
  connected-components : vector?
  isolated-vertices : vector?
  signed-component-volumes : vector?
  watertight? : boolean?
  orientable? : boolean?
  consistently-wound? : boolean?

An immutable, deterministic report over indexed geometry. Edge records retain first-triangle encounter order; components and loops retain source-index order. Degeneracy uses a tolerance proportional to the mesh’s squared extent rather than one universal world-coordinate epsilon.

procedure
(analyze-mesh3d mesh) → mesh3d-analysis?
mesh : mesh3d?

Computes topology and geometric diagnostics without changing mesh.

procedure
(mesh3d-validate mesh) → mesh3d-analysis?
mesh : mesh3d?

An explicit alias for analyze-mesh3d. Mesh construction remains cheap and does not implicitly run this potentially expensive analysis.

struct
(struct mesh3d-orientation-report ( initial-analysis
final-analysis
flipped-triangle-indices
outward?)
    #:transparent)
  initial-analysis : mesh3d-analysis?
  final-analysis : mesh3d-analysis?
  flipped-triangle-indices : vector?
  outward? : boolean?

An immutable explanation of an explicit orientation repair. Per-vertex normals are authored attributes and are not silently regenerated by repair.

procedure
(mesh3d-orient-consistently mesh)
→
mesh3d? mesh3d-orientation-report?
mesh : mesh3d?

Returns a replacement mesh with each manifold adjacent pair oppositely wound, or raises for degenerate, non-manifold, or parity-conflicting input.

procedure
(mesh3d-orient-outward mesh)
→
mesh3d? mesh3d-orientation-report?
mesh : mesh3d?

Additionally makes every closed, orientable, nonzero-volume component outward-facing. Open, non-manifold, non-orientable, and zero-volume components fail explicitly because they have no unambiguous outside.

procedure
(mesh3d-self-intersection-candidates mesh) → vector?
mesh : mesh3d?

Returns deterministic pairs of non-adjacent faces whose local AABBs overlap. This is a broad-phase candidate query, not a narrow-phase proof of intersection.

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