Replace Normals 3D Node

The normals of a mesh are vectors perpendicular to the surface that tell the render engine how light should reflect off it. With no normals or wrong normals, an object can look:

• Flat / dull - no lighting variation across the surface
• Faceted - every triangle stands out, no smoothing
• Lit inside out - light hits the wrong side

Replace Normals 3D sits in the stream of a 3D scene and recomputes the normals of every mesh. Lights, cameras and other non-mesh elements pass through unchanged.

• Effects Library: Tools > 3D > Replace Normals 3D
• Quick add: right-click in the Node Editor → Add Tool > 3D > Replace Normals 3D

Four typical situations where a mesh's normals are wrong and need to be recomputed:

1. After a Displace 3D / Custom Vertex 3D - the geometry was deformed but the normals still point in the old direction. The lighting follows the old shape and looks flat/inconsistent.
2. After a badly exported FBX import - some applications export normals inconsistently. Symptom: individually smooth triangles but visible transitions between adjacent triangles.
3. After a Triangulate 3D - triangulating a mesh can break the original smoothing.
4. For an intentional faceted look - deliberately apply a low smoothing angle to get a stylized low-poly render.

• SceneInput (orange) - required. 3D scene or geometry whose normals need to be recomputed.

Place the node right after the geometry source:

Shape 3D → Displace 3D → Replace Normals 3D → Merge 3D
FBX Mesh 3D → Replace Normals 3D → Merge 3D

No need to turn anything on - by default the node recomputes the normals with a standard smoothing angle, which already fixes 80% of cases.

Pre-Weld Position Vertices (default: off)

Merges positionally duplicated vertices before computing the normals without changing the output geometry. Essential to fix some OBJ/FBX imports that sometimes store the same vertex several times - the normal recompute then silently fails, and the duplicates create cracks in the smoothing.

Recompute (default: Always)

When to recompute the normals:

• Always - recomputes every frame. Guarantees consistency even if the mesh is animated/deformed.
• If Not Present - only computes if the mesh doesn't already have normals. Saves CPU.
• Never - never recomputes. Useful to freeze the normals at the first frame of an animation (otherwise the normals "jitter" from frame to frame).

Smoothing Angle (in degrees, typically 20° - 60°)

Adjacent faces whose angle (in degrees) is lower than this value get smoothed edges.

• 0° - faceted normals (each face independent) → low-poly look.
• 30° - the standard value for a "realistic" mesh with sharp edges.
• 60° - very smooth mesh, few visible edges.
• 360° - maximum smoothing, every edge smoothed (even right angles become rounded).

Ignore Smooth Groups (default: off)

Off: respects the existing smooth groups on the mesh (groups of polygons smoothed together). On: ignores the smooth groups and applies smoothing evenly based on the angle. Turn it on if you find the original smooth groups are poorly made.

Flip Normals (default: off)

Reverses the direction of the tangent vectors. The effect is mostly visible on meshes that use tangents (normal maps). Useful if a normal map looks visually inverted.

Smoothing Angle is the most visual parameter of the node. It sets the threshold angle below which adjacent faces are smoothed.

Concrete example: a cube

• The 6 faces of the cube form 90° angles with each other.
• With Smoothing Angle = 30° → 30° < 90°, the faces are NOT smoothed → a cube with crisp edges (the expected behavior).
• With Smoothing Angle = 100° → 100° > 90°, the faces ARE smoothed together → a cube that looks round (a strange effect).

Example: a sphere

A sphere is made of triangles with small angles (≈ 10-20° depending on the subdivision). A Smoothing Angle of 30° therefore smooths all of these angles → a perfectly round sphere. Lowering it to 5° would break the smoothing and give a faceted sphere.

• Post-Displace fix - the most common case. After a Displace 3D, place a Replace Normals with Smoothing Angle ≈ 30°. The lighting takes shape again.
• Repairing an FBX with broken normals - Pre-Weld Position Vertices on + Smoothing Angle 30° solves most messed-up imports.
• Stylized low-poly look - Smoothing Angle = 0° → an intentional faceted render, a very trendy effect in motion design.
• Smooth procedural modeling - after a Custom Vertex 3D has deformed some geometry, Replace Normals with a high angle for an organic render.
• Fixing an inverted normal map - if a normal map texture gives inside-out relief, enable Flip Normals.
• Optimizing a frozen animation - on an animated mesh whose topology doesn't change (only transforms), set Recompute = Never after a stable first frame to save CPU.

• Pitfall #1 - forgetting to add a Replace Normals after a Displace/Bender/Custom Vertex. The lighting looks "flat" and you look for the problem everywhere except here.
• Smoothing Angle 30° by default - a general rule that works on 90% of meshes. Only adjust it if the result doesn't look right.
• Enable Pre-Weld Position Vertices if the normals look "cracked" - often an import that duplicated vertices.
• Don't stack Replace Normals nodes - one is enough, placed after the last geometry transformation. Several in a row = wasted CPU.
• Flip Normals and complete visual inversion - if the whole mesh looks "inside out" (back face visible, front invisible), an external export has often inverted the normals. Flip Normals fixes it.
• If you want to mix smooth and faceted areas on the same mesh, use smooth groups in the source software instead, and leave Ignore Smooth Groups unchecked.