The `mime:` USD schema#

The attributes and applied schemas MIME writes on a stage’s prims and reads from them, all in its own namespace. An applied schema is written as a token of a prim’s apiSchemas, with no plugin, so any USD reads and writes it; an attribute is a custom attribute in the mime: namespace. The stage writer writes them on scene/scene.usda from the declarations alone, and a build reads the design data the schema puts on a referenced asset’s prims. The page built from this source adds, for each name, the constant that names it in the code, and for each registered geometry kind the settings it writes. The keys MIME writes in a layer’s own metadata (customLayerData), mime:recording on a recording’s layer and mime:visuals on a visuals layer, are not prims’ names and are not listed here.

Two checks hold this list to the code. mime docs check holds it to the constants scene/_compose.py and scene/_read.py read a stage with: each is here. (scene/_derived.py and viz/_visuals.py read names from a stage too, and are not scanned, so a name only they read is not required here.) tests/saved/test_usd_reference.py holds it to the stages the fixtures write, in both directions: every name a fixture’s stage authors is here, and every name here is authored on some fixture’s stage or is listed in docs/ratchets/usd_read_only.txt as one MIME only reads. That test plans the fixtures, which needs their assets, so a run without them does not exercise the second check.

A thing’s prim#

mime:thing: the kind of the thing whose prim this is (structure, medium, body or apparatus), on every thing’s prim, whether written by MIME or a prim an asset brings in and a body is bound to.
mime:name: the thing’s name in the experiment’s document, beside mime:thing.
mime:fills: on a medium’s prim, the region it fills, written as the document writes it (tube.lumen).

A geometry kind’s prim#

MimeGeometryAPI: applied on a prim that is a geometry kind, MIME’s or a referenced asset’s; a prim that writes mime:geometry attributes without it is refused at build.
mime:geometry: the registered name of the geometry kind the prim is.
mime:geometry:version: the registered version of that kind.
mime:geometry:<setting>: one of the kind’s shape settings, in SI with its unit in the attribute’s customData (units), on a kind with no native USD form; a whole number the kind holds (a screw’s starts) is written as a count, of unit one. A kind with a native form writes that primitive’s own attributes, in the stage’s units, instead. A build reads a referenced asset’s kind from the same attributes.
mime:representation: on a kind’s drawn mesh (its proxy child), what the mesh is, in words, for a reader of the stage.
mime:region: on a region’s own primitive below its kind’s prim (the tube’s lumen), the region’s name.
mime:derived_from: on a derived prim (a kind’s drawn mesh, a region’s primitive), the kind, the version and the parameters it was derived from, the parameters by the hash of their canonical form. A reader with only the stage tells a stale prim by it.
mime:derived_hash: on a derived prim, the hash of what it holds as written (a mesh’s points, counts and indices; a primitive’s attributes and transform), by which a reader with only the stage tells an edited one.

An apparatus’s chain and parts#

mime:segment: on a chain segment’s prim, the segment as its plan describes it.
mime:frame: on a frame’s prim below its segment, the frame’s own name, which the stage binding maps to its prim.
mime:mount: on a part’s prim, where it is mounted, <segment>.<frame>, or the world.
mime:solid: on a part’s prim, the geometry kind of its solid.
MimeMagnetAPI: applied on a part prim that carries a magnet’s design data.
mime:magnet:direction: the unit vector, in the part’s own frame, along which the part is magnetised. Written by MIME on an apparatus’s magnet part, and read from a referenced asset’s part prim, which must apply MimeMagnetAPI.

What the stage draws#

mime:visual:file: on a mesh visual of a chain’s frame, the file its description names, never its bytes.
mime:visual:asset: the manifest that lists the mesh (beside the description, or in an installed package), where one does, for the asset cache’s overlay.
mime:visual:sha256: the hash of the mesh file’s bytes, beside the manifest’s name.
mime:visual:role: what the shape stands for on its frame: visual, collision, or frames.
mime:vector:name: on the prim of a field a law reads at a body, the field’s interface name.
mime:vector:value: the field’s value at the body, set by a recording or a live client, in mime:vector:units.
mime:vector:units: the unit of mime:vector:value.
mime:vector:metres_per_unit: how long the drawn arrow is per unit of the field.

The names in the code#

Each documented name with the constant that names it where the code has one; the others are built where they are written (mime:<name> from a prim’s attributes, mime:geometry:<setting> from a kind’s settings).

Name	Constant
`MimeGeometryAPI`	`mime.scene._derived.GEOMETRY_API`
`MimeMagnetAPI`	`mime.scene._compose.MAGNET_API`
`mime:derived_from`	`mime.scene._derived.DERIVED_FROM`
`mime:derived_hash`	`mime.scene._derived.DERIVED_HASH`
`mime:fills`	built where it is written
`mime:frame`	built where it is written
`mime:geometry`	`mime.scene._derived.GEOMETRY`
`mime:geometry:<setting>`	built where it is written
`mime:geometry:version`	`mime.scene._derived.GEOMETRY_VERSION`
`mime:magnet:direction`	`mime.scene._compose.MAGNET_DIRECTION`
`mime:mount`	built where it is written
`mime:name`	built where it is written
`mime:region`	built where it is written
`mime:representation`	built where it is written
`mime:segment`	built where it is written
`mime:solid`	built where it is written
`mime:thing`	built where it is written
`mime:vector:metres_per_unit`	`mime.scene._stage.VECTOR_SCALE`
`mime:vector:name`	built where it is written
`mime:vector:units`	`mime.scene._stage.VECTOR_UNITS`
`mime:vector:value`	`mime.scene._stage.VECTOR_VALUE`
`mime:visual:asset`	`mime.scene._stage.VISUAL_ASSET`
`mime:visual:file`	`mime.scene._stage.VISUAL_FILE`
`mime:visual:role`	`mime.scene._stage.VISUAL_ROLE`
`mime:visual:sha256`	`mime.scene._stage.VISUAL_SHA256`

Each geometry kind on a stage#

A kind with a native USD form is that primitive; any other writes its shape settings, in SI, as mime:geometry:<setting>.

Kind	Version	Written as
`box`	0.1.0	`mime:geometry:size` (m)
`capsule`	0.1.0	its native USD primitive, Capsule
`capsule`	0.2.0	its native USD primitive, Capsule
`cylinder`	0.1.0	its native USD primitive, Cylinder
`ellipsoid`	0.1.0	`mime:geometry:semi_axes` (m)
`labx.bead`	0.1.0	`mime:geometry:radius` (m)
`screw`	0.2.0	`mime:geometry:length` (m), `mime:geometry:modulation` (1), `mime:geometry:radius` (m), `mime:geometry:starts` (1), `mime:geometry:wavenumber` (1)
`screw`	0.3.0	`mime:geometry:length` (m), `mime:geometry:modulation` (1), `mime:geometry:radius` (m), `mime:geometry:starts` (1), `mime:geometry:wavenumber` (1)
`sphere`	0.1.0	its native USD primitive, Sphere
`sphere`	0.2.0	its native USD primitive, Sphere
`tube`	0.1.0	`mime:geometry:inner_radius` (m), `mime:geometry:length` (m), `mime:geometry:wall` (m)