Geometry

Two attributes on geometry prims: crust:rayMask chooses which rays see a prim, and crust:motion:translate moves it during the shutter.

crust:rayMask

int, default 7 (every ray type).

Which kinds of ray see this prim. The value is a sum of bits:

bit	value	ray type
0	1	camera rays: the prim appears in the image
1	2	shadow rays: the prim casts shadows
2	4	indirect rays: the prim appears in reflections and refractions, and bounces light

Common values:

value	effect
`7`	visible to everything (the default)
`6`	invisible to the camera, still casts shadows and bounces light: a light blocker or bounce card
`5`	casts no shadows
`1`	seen by the camera only: no shadows, not in reflections
`0`	invisible to every ray

Read on Mesh, Sphere and BasisCurves prims, including prims inside instance prototypes. On a light, it replaces the light's default visibility; see Lights.

# A card that blocks light but doesn't appear in the image.
def Mesh "Blocker"
{
    int crust:rayMask = 6
    # ...
}

Use only bits 0–2. Crust Render uses the higher bits for UsdLux shadow linking (collection:shadowLink), and logs a warning if it has to overwrite bits you authored.

crust:motion:translate

float3, default none (no motion).

A world-space translation that the prim moves through while the shutter is open, for transform motion blur. The prim starts at its authored position when the shutter opens and has moved by this vector when it closes.

Read on Mesh and Sphere prims.

# A sphere that moves one unit to the right during the shutter.
def Sphere "Mover"
{
    double radius = 0.6
    float3 crust:motion:translate = (1, 0, 0)
    double3 xformOp:translate = (-1.5, 0.6, 0)
    uniform token[] xformOpOrder = ["xformOp:translate"]
}

This is the only kind of motion blur. There is no deformation (per-vertex) blur, and animated xformOps are read at the render frame only: they don't blur. A mesh with a non-invertible transform (for example, a scale of zero on one axis) can't move. Its crust:motion:translate is ignored with a warning.

samples/motionblur.usda shows both crust:motion:translate and crust:rayMask = 6.

crust:displacementBound

float, local units, on a Mesh prim or on its Material. The largest distance the material's displacement can move a vertex. The mesh prim's value wins. Next comes RenderMan's primvars:displacementbound:sphere on the mesh prim (the Moana Island authors it), then the material's crust:displacementBound.

Only adaptive subdivision (--subdiv-edge-length) reads it. Geometry outside the camera's view is diced coarsely, and displacement can push geometry into view. So the view test grows each mesh's box by this bound. A constant displacement needs none, since its bound is exact. A textured displacement with no bound skips the view test altogether, so it is diced by distance alone, in view or not, and --stats counts it as "frustum test skipped".

A bound that is too small is not enforced: the full offset is still applied, and one warning names the mesh.

def Mesh "Cliff" (prepend apiSchemas = ["MaterialBindingAPI"])
{
    float crust:displacementBound = 0.5
}

Standard geometry attributes

Crust Render reads these standard UsdGeom attributes without any crust: attribute.

attribute	effect
`subdivisionScheme`	any value other than `none` makes a mesh a subdivision mesh. Unauthored means `catmullClark`. The refinement level comes from `crust:subdivisionLevel`. A `none` mesh whose material displaces it is refined as `bilinear`: its faces stay flat until displaced. Its hard edges then soften, since the displaced mesh shades with smooth normals. The exception is a mesh with any non-quad face whose displacement reads Ptex: refining it would leave its triangles' children with no Ptex face, so it stays its cage, with a warning.
`visibility`, `purpose`	a prim with `visibility = "invisible"` is skipped with its whole subtree. Prims with purpose `guide` or `proxy` are skipped.
`primvars:st`	UV coordinates for UV and UDIM textures
`PointInstancer` and native instancing	prototypes are stored once and placed per instance

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