b3dVertexNX

Returns vertex normal X component (surface direction for lighting). Takes mesh (surface-based mesh entity), surface (surface handle, 0-based), vertexIndex (vertex number, 0-based). Returns normal X as double or 0.0 on error. Validates mesh exists, type is ENTITY_MESH, is surface-based, surface index valid, and vertex index valid. Returns surface->vertices[vertexIndex].normal.x directly. Returns 0.0 if: invalid mesh, not surface-based, invalid surface, vertex index out of range.

This function retrieves vertex normal X component for lighting and surface orientation analysis. Normal = normalized 3D vector indicating surface direction at vertex (perpendicular to surface). Normals critical for lighting: dot product of normal and light direction determines brightness (Lambertian shading). X component represents normal's rightward/leftward direction. Normal range: -1.0 to +1.0 (normalized vector), magnitude of full normal (nx,ny,nz) should be ~1.0 (Sqr(nx^2 + ny^2 + nz^2) ~ 1.0). Return value 0.0 ambiguous (could be normal pointing perpendicular to X-axis or error) - validate separately. Use cases: (1) Lighting calculation (dot product with light vector), (2) Backface detection (check normal vs view direction), (3) Surface orientation analysis (classify vertical/horizontal surfaces), (4) Reflection calculation (reflect view ray across normal), (5) Normal validation (verify normals are unit length). Common pattern: For i=0 To b3dCountVertices(mesh, surf)-1, nx=b3dVertexNX(mesh, surf, i), ny=b3dVertexNY(mesh, surf, i), nz=b3dVertexNZ(mesh, surf, i), length=Sqr(nx*nx + ny*ny + nz*nz), If Abs(length-1.0) > 0.01 Then Print "Warning: non-unit normal at vertex " + i. No X-axis negation: normal.x returned as-is. Normal generation: set via b3dVertexNormal or calculated via b3dUpdateNormals (averages adjacent triangle normals). Default normal: b3dAddVertex sets default normal to (0, -1, 0) = upward after negation - typically recalculated via b3dUpdateNormals. Smooth vs hard edges: shared vertices have averaged normals (smooth shading), duplicate vertices have different normals (hard edges). Normal direction: points outward from solid surfaces, inward-pointing normals cause inverted lighting (dark when should be bright). Precision: double precision (64-bit float). Alternative: calculate normal from triangle vertices via cross product, use tangent-space normals for normal mapping. Performance: fast direct array access.