b3dVertexV

Returns vertex V texture coordinate (vertical texture mapping). Takes mesh (surface-based mesh entity), surface (surface handle, 0-based), vertexIndex (vertex number, 0-based), coordSet (UV set index, currently ignored - always returns base UV set 0). Returns V 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].texCoord.y directly. coordSet parameter ignored (only one UV set currently supported). Returns 0.0 if: invalid mesh, not surface-based, invalid surface, vertex index out of range.

This function retrieves vertex texture V coordinate for vertical texture mapping. UV coordinates map 2D texture onto 3D mesh surface. U = horizontal (left-right), V = vertical (up-down). V coordinate convention: 0.0 = top edge of texture, 1.0 = bottom edge, 0.5 = center. Values outside 0-1 range valid: causes texture tiling/wrapping based on sampler settings (repeat, clamp, mirror). Return value 0.0 ambiguous (could be top edge mapping or error) - validate separately. Use cases: (1) Vertical texture alignment (check V coordinates for proper top/bottom mapping), (2) Texture scrolling (animate V coordinate for waterfall/conveyor effects), (3) UV bounds calculation (find min/max V for validation), (4) Lightmap UVs (second UV set for baked lighting), (5) Atlas packing (verify V coordinates within atlas region). Common pattern: For i=0 To b3dCountVertices(mesh, surf)-1, u=b3dVertexU(mesh, surf, i, 0), v=b3dVertexV(mesh, surf, i, 0), newV = v + scrollSpeed, b3dVertexTexCoords(mesh, surf, i, u, newV, 0). coordSet parameter: reserved for multi-UV support (base texture uses set 0, normal/lightmap could use set 1), currently only coordSet=0 implemented, other values return base UV. UV storage: texCoord.y component of 2D vector in vertex structure. V origin: 0.0 = top edge (matches image origin top-left). Typical V values: 0.0 to 1.0 for single texture, 0.0 to N for vertical tiling. V setting: set via b3dAddVertex or b3dVertexTexCoords. V generation: procedural UV mapping functions (b3dUVMapPlanar/Box/Cylindrical/Spherical) calculate V based on geometry. Alternative: batch UV modification, use vertex shader for dynamic UV animation. Precision: double precision (64-bit float). Performance: fast direct array access. Texture sampling: GPU interpolates V across triangle, samples texture at (U,V) coordinate. V-axis flipping: some formats require V-flip (1.0-V) for correct orientation - BambooBasic handles automatically.