MaterialXLoader: added invert implementation

[beersandrew]

• allow invert to be a number, vec 2|3|4, or color, subtracting the value from an optionally inputted amount field (which is defaulted to all parts 1 of the input type)

Related issue: #29432

Description

Implemented the invert node for the MaterialXLoader

This contribution is funded by Needle

[sunag]

The implementation of #29440 should be simple, in case you want to implement this PR?

const extract_x = ( in1 ) => in1.x;

The index parameter seems redundant here based on the function name...

[beersandrew]

The implementation of #29440 should be simple, in case you want to implement this PR?

const extract_x = ( in1 ) => in1.x;

The index parameter seems redundant here based on the function name...

I think it's needed, here the name is only an identifier with extract being the node name(https://github.com/beersandrew/MaterialX/blob/separateNodeExample/resources/Materials/Examples/StandardSurface/extract.mtlx#L8)

not sure if this works? but this is the route i'll try (should work for colorN & vectorN)

const extract = ( in1, index ) => in1[index];

[sunag]

I think it's better to use element in this case, with [ index ] the input values ​​should be just integer js numbers not nodes.

const extract = ( in1, index ) => in1.element( index );