Eye Material

Eyes matter far out of proportion to their screen area — they are the first thing a viewer looks at, and their characteristic features (the iris displaced by corneal refraction, the sense of pupil depth, the dark ring at the edge) are exactly the things a general PBR material cannot express.

EyeMaterial shades the whole eyeball — sclera, limbus and iris — from one mesh and one material.

Asset requirements

This approach needs no mask texture: the regions are derived analytically from the UV distance to the iris centre. The cost is that the asset must follow a convention:

• A single eyeball mesh (sphere or front dome), carrying both normals and tangents. Without tangents there is no TBN and refraction degrades to a flat iris — the most common problem.
• UVs must place the pupil centre at irisCenter (default (0.5, 0.5)), with the iris occupying a disc of radius irisRadius (default 0.22) around it.
• The iris texture must have the pupil at its centre. A sclera texture is optional; without one the sclera is shaded from scleraColor.

If the iris is in the wrong place or the wrong size, check the UV layout and these two parameters before touching refraction.

Iris and cornea

Property	Default	Purpose
irisCenter	(0.5, 0.5)	Pupil centre in UV space
irisRadius	0.22	Iris disc radius (UV units)
irisDepth	0.06	Iris depth below the corneal surface, driving parallax strength
ior	1.376	Corneal index of refraction; 1.376 is the measured human value
pupilRadius	0.35	Pupil radius, relative to the iris
pupilDilation	0	Pupil scaling, for lighting changes or emotion
irisColor	—	Iris tint
irisBrightness	—	Iris brightness
corneaSpecularStrength	—	Corneal highlight strength
corneaRoughness	0.05	Corneal roughness — very low, the cornea is nearly a mirror

irisDepth and ior together set how strong the parallax is. Increase irisDepth for a deeper look, but too much gives the illusion away at grazing angles.

Limbus and sclera

Property	Default	Purpose
limbalRingWidth	0.15	Width of the dark ring at the corneal edge
limbalRingStrength	—	Ring strength
scleraColor	—	Sclera colour, used when there is no texture
scleraWrap	0.35	Wrap diffuse on the sclera, softening the terminator
scleraEdgeTint	—	Sclera edge tint, approximating vessels and shadowing

The limbal ring is one of the details that sells an eye as real. Real irises have a band of pigment at their outer edge, and without it eyes look flat and textured-on.

Socket occlusion (optional)

A bare eyeball lights up uniformly under ambient light, because it does not know it sits inside a socket. The engine offers two complementary occlusion layers, both off by default.

Analytic socket occlusion

material.socketOcclusion = true;
material.upperLidAngle = 50;   // degrees
material.lowerLidAngle = 65;

This models the lids as an asymmetric aperture: around an axis fixed in the eyeball's object space (rotatable via socketRotation), with separate upper and lower opening angles. Directions outside the aperture darken ambient diffuse, ambient specular and direct lights. No mask texture, extra pass or per-frame scripting is involved.

Using object space means the occlusion frame follows skinning and node motion automatically, and vertical gaze drags the occlusion along with the eye — approximating how real upper lids follow it. Horizontal gaze rotating about the up axis leaves the occlusion unchanged, which also matches reality.

socketOcclusionSoftness and socketOcclusionStrength tune the transition and the amount.

If nothing changes, check vertexNormal first

Socket occlusion is gated on vertexNormal. If you set socketOcclusion = true and see no difference, make sure vertexNormal is enabled.

Screen-space contact occlusion

material.contactAO = true;

The analytic aperture is a model of the lids; this layer reads the depth prepass and therefore follows the real lid mesh — blinks, asymmetry, lashes and all.

It dims the ambient terms and the diffuse response of direct lights (whose shadow maps cannot resolve the millimetre lid gap), but leaves direct specular untouched so the corneal highlight survives.

Related parameters: contactAORadius (default 0.006), contactAOMinDistance, contactAOMaxDistance, contactAOStrength and contactAOTemporalJitter.

Requires a depth prepass

This layer depends on a depth prepass. The Forward+ pipeline always runs one, so it is normally available; where none is bound the term silently resolves to no occlusion rather than erroring.

Both layers can be enabled together: the analytic one provides stable base occlusion, and contact occlusion adds the dynamic detail of the real lids.

See also

• Skin and Subsurface Scattering — the skin half of character rendering
• Hair Rendering — the hair half of character rendering
• Custom Materials — the general material system