Extending mix node to allow per channel mixing

[friedererdmann]

Hello,

we're trying to currently match a large number of shaders that have been created in a game engine to MaterialX counter parts. Our current shaders are making use of HLSL code.

While trying to translate the functionality of lerp from HLSL we tried matching it to MaterialX' mix node, which seems to serve the same purpose. However, mix only takes a float as blend argument, making per-channel interpolation impossible.

I'd like to ask if it would be possible to overload mix to also allow the mix input to match the data type of fg/bg to allow per channel blending?

The same change would most likely benefit also most other compositing nodes.

[jstone-lucasfilm]

This sounds like a good proposal to me, @friedererdmann. Feel free to write up a pull request for this change if you have the bandwidth, and we'll plan to update the specification for mix and other similar nodes in the 1.39 specification.

[friedererdmann]

I've started experimenting here https://github.com/friedererdmann/MaterialX/tree/extend_mix_datatypes but since this is my first contact with MaterialX' codebase, I'm very open to suggestions if I approach this correctly.

[jstone-lucasfilm]

Thanks for this original report, @friedererdmann, as well as for the fix in #1077!