The Transform expression converts a threechannel vector value from one reference coordinate system to another.
By default, all shader calculations in a material are done in tangent space. The vector constants, camera vector, light vector, etc are all transformed to tangent space before being used in a material. The Transform expression allows these vectors to be transformed from tangent space to worldspace, localspace, or viewspace coordinate systems. In addition, it allows worldspace and localspace vectors to be transformed to any of the other reference coordinate systems.
Item
 Description


 
Source
 Specifies the current coordinate system to transform the vector from. This can be one of: World, Local, or Tangent.

Destination
 Specifies the target coordinate system to transform the vector to. This can be one of: World, View, Local, or Tangent.

The Transform node accounts for mirrored UVs, thus allowing, for example, highlights that only affect the right edge of a character.
The Transform node is useful for generating world space normals for sampling a cubemap. A normal map can be transformed to world space. Below is an example of transforming normals to world space in order to sample a cubemap:
Transforming normals to view space can be used for creating edgeon effects. This can be achieved by using mesh normals to generate texture coordinates (commonly referred to as "Sphere Mapping"). With this method, normals facing directly at the camera will map to the center of the texture coordinates, and normals facing perpendicular to the camera will map at the edge of the texture coordinates. Here is an example of Sphere Mapping:
A constant3vector with a value of (0,0,1) is fed into the Transform with TRANSFORM_View set, which is then passed through a ComponentMask (Passing through only R and G). Since the Transform will output a range of values from 1 to 1, we must bias the values to put them into the 01 range. This is done by multiplying by 0.5, and then adding 0.5. Then simply plug that into the Coordinates of a texture. Any texture will work; I made one with three rings so that the effect is obvious.
To use this effect with a normal map, simply substitute the Constant3Vector with a normal map texture.
Here is an example of this spheremap material applied to a bloblike rock mesh:
VertexColor is mutually exclusive with the Transform node due to limited interpolators. If you use both a Transform node and VertexColor, then VertexColor will come out all white.
The transform node currently does not handle nonuniform scaling correctly.