How to define outAlpha connection in materialx

[joey.skeys]

nodes that are defined with output color3 could have an alpha output in maya, e.g MayaFile, how to define outAlpha connection in materialx?

[Stephen.Blair]

MtoA does not send a MayaFile node to Arnold.

MayaFile is converted to an image node, possibly with other shader nodes (such as color_correction).

file.outAlpha becomes a connection to the "a" channel of the image node output

Your materialx document should use only Arnold nodes.

[joey.skeys]

My bad, MayaFile is not a good example.

let's say, what if I connect the alpha output of AiImage to a float plug. It seems we can only have fixed type output of a specific node and the output of AiImage is color3, what to do if I use the alpha channel(in MaterialX).

[Stephen.Blair]

If you connect the alpha output of AiImage, then image.a is connected. For example:

standard_surface
{
 name aiStandardSurface1
 base aiImage1.a
 base_color aiImage1
}


image
{
 name aiImage1
 filename "noicon.pic"
 missing_texture_color 0 0 0 1
}

[joey.skeys]

Okay, I see. And then, is there any way to denote such kind connection in materialx? From what I know, output of AiImage could be color4, maybe I should put a rgba_to_float node in between?