b3dVertexX

Returns vertex X position coordinate. Takes mesh (surface-based mesh entity), surface (surface handle, 0-based), vertexIndex (vertex number, 0-based). Returns X coordinate 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].position.x directly. Returns 0.0 if: invalid mesh, not surface-based, invalid surface, vertex index out of range.

This function retrieves vertex position X component for mesh analysis and modification. Position stored as 3D vector (x, y, z) - this function returns X only. X-axis convention: positive X = right, negative X = left (right-handed coordinate system). Return value 0.0 ambiguous (could be vertex at origin or error) - validate mesh/surface/vertex separately if needed. Use cases: (1) Vertex position queries (read geometry data), (2) Bounding box calculation (find min/max X), (3) Collision detection (check vertex positions against boundaries), (4) Mesh analysis (measure dimensions, center of mass), (5) Vertex modification validation (verify b3dVertexCoords worked). Common pattern: For i=0 To b3dCountVertices(mesh, surf)-1, x=b3dVertexX(mesh, surf, i), y=b3dVertexY(mesh, surf, i), z=b3dVertexZ(mesh, surf, i), process position (x,y,z). No Y-axis negation: X coordinate returned as-is (unlike b3dVertexY which negates for DirectX convention). Coordinate system: right-handed, Y-up (Y+ = up, Y- = down), X+ = right, Z+ = forward. Precision: double precision (64-bit float) for accurate position values. Vertex position set via b3dAddVertex or b3dVertexCoords - this function only reads, doesn't modify. Alternative: batch read all vertex positions, use b3dCopyMesh to extract entire geometry. Performance: fast direct array access, no computation. Typical values: vertex positions range from model-space coordinates (e.g., -10.0 to +10.0 for small objects, -1000.0 to +1000.0 for terrain). World position: vertex position in local model space - transform by entity position/rotation/scale (b3dEntityX/Y/Z, b3dEntityPitch/Yaw/Roll) for world coordinates.