Blinn

Blinn is one of Fusion's classic illumination materials. It does not create geometry or assemble a scene; it describes the surface response of existing geometry: base color, highlight, transparency, light transmission and participation in scene lighting and shadows.

The standard Material controls embedded in many 3D geometry nodes are conceptually similar to a simplified Blinn. The standalone Blinn node becomes especially useful when the surface needs external diffuse, specular color, specular intensity, specular exponent or bump maps.

Blinn has five inputs, not one generic MaterialInput: Diffuse Material, Specular Color Material, Specular Intensity Material, Specular Exponent Material and Bump Map Material.

The first four inputs accept either a 2D image or 3D material. They multiply the corresponding Inspector values rather than replacing them. A neutral white map generally preserves the base contribution, black suppresses it locally, and intermediate values scale it.

Diffuse Material uses RGB as the primary surface texture while the map alpha participates in material alpha. Placement of a 2D texture depends on the geometry UVs, so incorrect UV mapping is not something the Blinn shader can repair by itself.

Specular Color Material modulates highlight color independently from the diffuse surface. This lets the base color remain unchanged while highlight color is altered or suppressed in selected UV areas.

For a 2D Specular Intensity Material, Fusion uses alpha as the scalar map and discards RGB. A visually high-contrast RGB image with constant alpha therefore will not behave like an intensity map until its alpha channel is authored correctly.

Specular Exponent Material follows the same scalar logic: a 2D image contributes through alpha, multiplying the base Exponent and changing highlight falloff/size rather than overall strength.

Bump Map Material is the special fifth input. It accepts 3D material data. The normal workflow is 2D height/texture → Bump Map → Blinn.Bump Map Material, rather than feeding a normal 2D image directly into the bump socket.

Bump changes normals used for lighting but does not deform the actual silhouette. If the edge of the object must physically change, use geometry/displacement rather than escalating bump strength.

Fusion's Blinn model calculates the highlight from the surface normal and the half-angle vector between the light and viewer. In practical tuning, Specular Intensity controls strength while Exponent controls falloff and compactness, so they should be tested separately.

Diffuse Alpha and Opacity both affect transparency but are easier to reason about when tested independently. Alpha belongs to the material/diffuse alpha path, while Opacity scales the visible diffuse/specular contribution; moving both together obscures cause and effect.

Transmittance is not a synonym for Opacity. Opacity describes surface visibility, while Transmittance describes how light passes through the material and how transmissive shadows are formed. A visually dense surface can still transmit colored light under the right settings.

Attenuation controls the color/amount of transmitted light. A tinted value can produce stained-glass-like colored shadows; black is not a neutral transparent state but blocks the corresponding transmission.

Alpha Detail controls how diffuse-material alpha participates in transmissive shadow density. It is not a generic alpha quality or feather slider and should be judged on a surface that actually casts a shadow.

Color Detail brings diffuse/texture color into transmitted light and shadows. Saturation then controls the saturation of that color component, so establish Color Detail first and tune Saturation second.

Receives Lighting and Receives Shadows are independent flags. The first controls participation in 3D lighting; the second controls whether the surface receives shadows. Disabling one does not implicitly disable the other.

Two Sided Lighting should not be reduced to a simple back-face visibility switch. It adds a reverse-facing set of normals so planes and open geometry can respond to lighting from both sides.

Material ID is rendered into the MatID auxiliary channel only when the corresponding output is enabled in Renderer3D. Setting a number in Blinn does not create a visible 2D mask by itself and does not replace normal alpha.

Blinn outputs Material, not image and not scene3d. The correct boundary is texture maps → Blinn.Material → Geometry.MaterialInput → Merge3D scene → Renderer3D → 2D RGBA image.

With five closely packed inputs, do not guess tiny connectors. Dragging a source onto the material node with Alt/Option or right-drag exposes an input menu, which is safer for targeting the intended socket.

Diagnose Blinn on simple curved geometry with one light. Establish neutral diffuse and base specular first, then add one texture input at a time, followed by bump, transmittance, Two-Sided Lighting and finally technical IDs/passes.

The bundled Inspector capture confirms Diffuse RGBA/Opacity, Specular RGB/Intensity/Exponent, Transmittance Attenuation RGB/Alpha Detail/Color Detail/Saturation, Receives Lighting/Shadows, Two Sided Lighting and Material ID. The five Flow inputs are documented by Blackmagic's 3D Material reference and remain a target-build live-verification item for final workstation certification.