material-preview-surface-present#

Code	VM.PS.002
Validator	latest+
Compatibility	open-usd
Tags	✅

Summary#

A renderable GPrim’s material must connect a UsdPreviewSurface on outputs:surface.

Description#

A renderable GPrim resolves a material binding at the full purpose. That material MUST connect outputs:surface.

outputs:surface is the universal render context, the surface a consumer gets when it names no context. The universal context is the last entry in USD’s resolution order, so a material with nothing connected there does not fall through to its MaterialX or MDL surface. The consumer gets the renderer’s default material.

com.nvidia.usd.VM.PS.001 governs how a UsdPreviewSurface is authored, and reports nothing about an asset that has none, because it inspects a shader that is not there. A profile requiring the preview surface lists both codes.

A GPrim that resolves no material at all is reported by VM.MAT.001.

Two subjects, and why#

The requirement is written for two shapes of asset.

An asset with geometry. The subject is the geometry a final render draws: a GPrim whose computed purpose is default or render, and the material it resolves at the full purpose. Every such material MUST connect the terminal. Proxy and guide geometry, materials bound only through material:binding:preview, unused entries in /Looks, and friction-only physics materials are all outside the subject, so no exception has to be written for them.

An asset that is a material. A material library publishes Material prims and no geometry to bind them to. Against the first subject such an asset has nothing to judge, so the requirement would report nothing and the feature would state nothing a consumer could act on. Where the stage has no geometry a final render would draw, the subject becomes the Material prims, and at least one of them MUST connect the terminal.

The second branch asks for one rather than all, because an asset with no geometry gives no way to say which of its materials a consumer will use. On an asset with geometry the first branch is the stronger statement and the second does not run — so an unused material carrying the terminal can never stand in for a bound material that lacks it.

VG.MESH.001 uses the same stage-level shape to require that a stage contains at least one mesh.

Why is it required?#

UsdPreviewSurface is the surface every OpenUSD consumer can evaluate. An asset without one renders on the consumer’s default material wherever MDL and MaterialX are unavailable
A feature built only from requirements that inspect a surface when they find one passes an asset that has no such surface. FET_006_STANDARD then states nothing a consumer can act on, and a library searching validation results cannot use it to find the assets it can render

Examples#

Valid: a bound material connects the universal terminal#

def Material "Chrome"
{
    token outputs:surface.connect = </World/Looks/Chrome/Preview.outputs:surface>
    token outputs:mtlx:surface.connect = </World/Looks/Chrome/OpenPBR.outputs:out>

    def Shader "Preview"
    {
        uniform token info:id = "UsdPreviewSurface"
        color3f inputs:diffuseColor = (0.8, 0.8, 0.8)
        float inputs:metallic = 1
        float inputs:roughness = 0.2
        token outputs:surface
    }
}

Invalid: OpenPBR alone#

def Material "Chrome"
{
    token outputs:mtlx:surface.connect = </World/Looks/Chrome/OpenPBR.outputs:out>
}

A consumer without MaterialX gets its own default material for every GPrim this is bound to.

For more information#

How to comply#

Connect a UsdPreviewSurface shader to the Material prim’s outputs:surface. The name of the shader output it connects to is unconstrained.