There is a very limiting problem with the Render Map function (in Slate as well as MAXScript) regarding OSL and Substance Maps (and Map Output Selector)--you cannot render out an alpha channel from the texture node.
I propose that there is a new option in Render Map (both Max UI as well as MAXScript) that allows users to set the alpha based on different sources in a map.
In the Render Map UI there should be an optional drop down that lists available outputs from a OSL Map/Substance map that is the source of a Map Output Selector to use as the source of the alpha channel. For example, if the OSL Map has these outputs: diffuseColor and diffuseAlpha, the renderMap dialog includes those maps in a drop down. The same functionality should be added to the MAXScript renderMap() function. This should default to the next idea (below).
Alternatively, the function could be controlled in a new parameter that is available in the OSL Map and Map Output Selector nodes that provide the same kind of functionality. For example, these texture nodes get a new parameter called Alpha Source that is used by default when rendering and outputting to other nodes in a shader tree.
Of the two methods described above (updating the rendermap() function to give user a choice VS updating the OSL Map and Map Output Selector textures themselves with the new setting) I personally prefer updating the OSL Map and Map Output Selector (and having the render map simply honor this new alpha source in the textures).
Either way, it is very important to add support for the alpha channel in those texture maps.
