depth-scaled-tangent-normals Specification

Purpose

TBD - created by archiving change scale-tangent-normals-with-depth. Update Purpose after archive.

Requirements

Requirement: Normal strength follows geometry depth scale

When a Geometry Nodes group both exposes Depth Scale and is rendered with a normal map, it SHALL store 1 - Depth Scale as the o_normal_reduction float attribute on its final geometry. O Image Layer SHALL calculate Tangent and Object Normal Map Strength as its Normal Scale input multiplied by 1 - o_normal_reduction.

Scenario: Reduced relief depth reduces Tangent normal strength

WHEN an O Image Relief Plane uses a Tangent normal map and Depth Scale is set to 0.5
THEN the Tangent Normal Map Strength is one half of the value produced at Depth Scale 1 with the same Normal Scale input

Scenario: Zero relief depth disables Tangent normal detail

WHEN an O Image Relief Plane uses a Tangent normal map and Depth Scale is set to 0
THEN the Tangent Normal Map Strength is zero

Scenario: Depth extrapolation is preserved

WHEN an eligible Tangent-normal geometry group uses Depth Scale greater than 1
THEN o_normal_reduction is negative by the corresponding amount and the Tangent Normal Map Strength retains the extrapolated value without clamping

Requirement: Reduction attribute retains its material fallback

O Image Layer SHALL use a factor of 1 for its Tangent Normal Map Strength when o_normal_reduction is absent. The existing o_normal_reduction material contract SHALL remain unchanged.

Scenario: Ordinary image material has no normal-scale attribute

WHEN an object using O Image Layer has no o_normal_reduction attribute
THEN its Tangent Normal Map Strength equals the Normal Scale input

Scenario: Object Space normal strength follows the reduction

WHEN O Image Layer is configured for an Object Space normal map and its geometry has any o_normal_reduction value
THEN the Object Space Normal Map Strength equals the Normal Scale input multiplied by 1 - o_normal_reduction

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