add combine9 and combine16 so we can create matrices

[lucap-sidefx]

I think Rafal brought this up on the slack channel, but I wanted to put in here so it doesn't get forgotten.

add comibine9 and combine16 so we can create custom matrices in our shaders.

[kwokcb]

constant (matrix33 and matrix44) already exist so curious if those cannot be used ? e.g. They don't provide the ability to have upstream connections since there is only 1 input. In this case perhaps a variant on constant with 9 or 16 inputs to produce a matrix33 or matrix44 could be another option and might be clearer than a using a combine ?

Just some thoughts.

[dbsmythe]

In the WIP v1.39 Specification, there is a new proposed node, that takes 3 vector3 or 4 vector4 row vectors, and creates a 3x3 or 4x4 matrix from them. Those inputs could be connected to existing standard or nodes if you wanted to start with floats rather than row vectors. Would this proposal address the request?

[jstone-lucasfilm]

Thanks for this original report, @lucap-sidefx, and I believe this is now addressed with the merge of #1553.