ptransform VEX function

Transforms a vector from one space to another.

Contexts: image3d, chop, cop, pop, sop, surface, displace, fog, light, shadow, photon, cvex

vector ptransform(vector , matrix )
vector ptransform(string tospace, vector v)

Transforms from “space:current” (see below).
vector ptransform(string fromspace, string tospace, vector v)

The transform functions let you transform a vector from one space to another.

ptransform interprets the vector as a position.
vtransform interprets the vector as a direction vector, and so doesn’t apply the translations from the matrix.
ntransform interprets the vector as a normal vector, and so multiplies by the inverse transpose of the matrix (ignoring the translations).

The possible values for the space arguments are:

An object path	Use the object space of an object specifed by a path string. Tip In some cases, such as point instancing, mantra may automatically mangle object paths. You can generate an `.ifd` file and look inside to try to find what mantra is calling the object you want.
`"space:object"`	Object space of the current object.
`"space:world"`	Houdini world space.
`"space:camera"`	mantra camera space.
`"space:texture"`	Space assigned to the current shader.
`"space:ndc"`	Normal Device Coordinate space.
`"space:current"`	The current space the vector is in.
`"space:world"`	Houdini world space.

The version with only a tospace argument assumes fromspace is “space:current”. For example:

Pworld = ptransform("space:world", P);

…is equivalent to:

Pworld = ptransform("space:current", "space:world", P);

Examples

Transform a vector from its current space to object space:

ospace = ptransform("space:object", P)

Transform a vector from object space to mantra’s natural coordinate space (“camera” space):

ospace = ptransform("space:object", "space:current", P)