ReplaceNormals3D

ReplaceNormals3D accepts one required SceneInput carrying classic Fusion scene3d and returns the same data domain through Output. It is a geometry/shading processor; pixels appear only after Renderer3D.

Blackmagic describes ReplaceNormals3D as replacing normals and tangents on incoming geometry. All polygon meshes in the input scene are affected, while lights, cameras, point clouds, locators, materials, and other non-mesh scene objects pass through unaffected.

The tool operates on per-vertex normals and tangents rather than per-face vectors. It does not generate a normal-map image or replace a material shader; it changes the surface vectors consumed by lighting and bump-dependent shading.

Pre-Weld Position Vertices is a computation helper, not a permanent mesh weld. It temporarily treats coincident position vertices as welded while normals/tangents are calculated, then discards that pre-weld result. Output position topology should remain unchanged by this control.

If you need to actually merge position vertices and change adjacency/topology on the output mesh, use Weld3D as a separate upstream stage. ReplaceNormals3D Pre-Weld is not a substitute for Weld3D.

Normals / Recompute selects the policy: Always replaces/recalculates normals every time, If Not Present only creates them when they are missing, and Never performs no new normal generation. The historical tool reference also notes Never as useful in animation workflows where repeated recomputation is not wanted.

Smoothing Angle defines which neighboring faces may share smoothed reconstructed normals. Blackmagic gives roughly 20–60 degrees as a typical working range, but that is not a preset; the correct threshold depends on mesh shape and intended hard edges.

The documentation defines a special case at Smoothing Angle = 0 degrees: faceted normals are produced. This is a useful diagnostic state because it exposes face-level shading without moving any mesh positions.

Ignore Smooth Groups changes the role of imported smooth-group boundaries. With the option off, faces in different smooth groups will not be smoothed across even when the angle would otherwise allow it; with it on, Smoothing Angle can become the dominant boundary test.

Flip Normals reverses normal direction. It is useful for diagnosing reversed surface orientation, but it is not a universal repair switch: wrong topology, culling, or lighting may be the real upstream cause.

Tangents / Recompute uses the same Always / If Not Present / Never policy, but tangent calculation has an additional requirement: the input geometry must have usable texture coordinates. Without UV/UVW coordinates, a correct texture-aligned tangent basis cannot be constructed.

Flip Tangents U and Flip Tangents V reverse the tangent basis along the corresponding texture directions. These controls matter primarily in bump-mapping and other material workflows that actually consume tangents.

Blackmagic also warns that most Fusion primitives do not store tangents in advance. Renderer3D can generate and cache them on demand when a material needs bump mapping; ReplaceNormals3D is useful when that tangent generation must be controlled explicitly before the renderer.

This explains why Flip U/V can appear to do nothing: if no tangents exist yet and no downstream material consumes them, the beauty image may not visibly change. Test tangent controls on geometry with UVs and a real bump-dependent material.

Do not automatically recompute normals just because lighting looks unfamiliar. The historical reference warns that baked high-poly-to-low-poly bump workflows can be linked to the original authored normals, so replacing those normals can make the intended surface detail look worse.

Ordering relative to transforms matters. Blackmagic notes that ReplaceNormals3D calculations are done in each geometry's local coordinates rather than the ReplaceNormals3D tool coordinate system; an upstream non-uniform scale can therefore cause problems. A reliable baseline is to recompute normals/tangents before downstream non-uniform Transform3D scaling.

ReplaceNormals3D does not change UV coordinates. If the problem is texture placement, a UV seam, or missing coordinates, use UVMap3D or repair the source mesh; tangent recomputation is not UV generation.

The node is not a remesh, triangulation, or decimation tool either. Face/position topology belongs to Triangulate3D, Weld3D, or an external DCC depending on the problem; ReplaceNormals3D leaves those structural layers separate.

Because every mesh in the incoming scene can be affected, selective repair is safer on an isolated branch before Merge3D. Otherwise a normal policy intended for one object may unexpectedly alter the shading of another mesh already present in the same scene stream.

For diagnosis, separate four causes: position/topology continuity, normals/smooth groups, UV/tangents, and material. Change one layer at a time and compare bypass under simple directional lighting.

The bundled Resolve captures confirm the current captured Inspector labels: Pre-Weld Position Vertices, Normals Recompute, Smoothing Angle, Ignore Smooth Groups, Flip Normals, Tangents Recompute, and Flip Tangents U/V. This authoring pass did not execute live Resolve 21/21.1 mesh validation, so production-mesh behavior remains a target-build verification item.

Renderer3D remains the data boundary. ReplaceNormals3D.Output can continue into Transform3D, Merge3D, ReplaceMaterial3D, UVMap3D, or other compatible 3D processors; MediaOut and ordinary 2D effects only become valid after Renderer3D.Image.