directx11 - Do the predefined HLSL semantics carry any meaning?

I'd say there are 3 kinds of HLSL semantics:

• SV_* group - these are "system value" semantics which DO carry special meanings (e.g. assign special input/output data to/from shader stages)


• predefined semantics - e.g. NORMAL, POSITION and so on... They are mentioned in the docs but I failed to find any special meaning assigned to them


• semantics defined be the user - which can be anything (e.g. MY_AWESOME_TEXTURE_SEMANTIC) which apparently have no special meaning either

In addition, the docs say that more than one input/output value can have the same semantic assigned (e.g. 'NORMAL2 and NORMAL2). I guess that it doesn't include the SV_* group, though.

So besides the first group - do semantics carry any meaning at all? Do they even serve any purpose at all? :P

Answer

Do they even serve any purpose at all?

Yes for the user and developer of the shader, semantics conveys information about the intended use of a parameter. So you will know that POSITION is intended to be used as vertex position, NORMAL as vertex normal etc. Think of this as in-code documentation (not strictly the same though).

Do semantics carry any meaning at all?

They don't carry a meaning for the system, as they are not interpreted, but again for the user. You don't want to give vertex position a NORMAL semantic, it's really like deceiving the user/developer of the shader, it's confusing, it's like writing wrong documentation.