I can't see the Arnold properties of a Shape node

Maya must load the MtoA plug-in before any object is opened in the UI. This is a feature of the way that Maya works (once it has evaluated an AE template once it won't refresh it). The best thing to do is to ensure that MtoA is set to auto-load, then this issue cannot occur.

File name prefix doesn't work with AOVs

When rendering out AOVs, if you have a "File name prefix" in the file output part of the common tab, like "awesome_render", it won't render any of the AOV passes whether they are enabled or not. This is a Maya problem. Its method to compute the actual file names ignores some of its parameters when an explicit "File Name prefix" is set. Try using the <RenderPass> token in the file name. That's the closest Maya equivalent to AOVs, and it should be replaced by the AOV name.

I can't see render swatches in my custom shaders

You need to set their category for Maya to know it should swatch them with Arnold. It can be set in metadata, either in the source code:

AiMetaDataSetInt(mds, NULL, "maya.id", 0x00115H09);
AiMetaDataSetStr(mds, NULL, "maya.classification", "shader/surface");

Or in an .mtd file within your shaders library. This should be the same name and place of the .so/dll. For instance:

[node FB_skin] 
	desc 					STRING "Skin Shader." 
	maya.id 				INT 0x00115H09 
	maya.name 				STRING "aiFbSkin" 
	maya.classification 	STRING "shader/surface"

Custom Arnold lights don't appear in light Linking Window

Currently, Arnold custom lights like skydome and area will not appear in the light linking window. 

A workaround is to use the defaultLightSet to change light linking options for Arnold lights (make sure to refresh the IPR when making changes in the light linking window).

A video demonstrating this process can be found here.

Arnold Standins should appear in the light linking window (see image below).


NURBS tesselation

MtoA relies on Maya to tesselate the NURBS before sending it to Arnold as a polymesh. MtoA does not support simple 'Simple Tesselation Options', however, it does support the 'Primary Tesselation Attributes' under 'Advanced Tesselation' (see images below):


Shadow terminator effect

This is a self-shadowing error that can result from low tessellation or when objects do not have thickness. It usually occurs in concave areas or when the light is behind the polygon mesh. In these situations, it can introduce light leaking.

There are some workarounds:

  1. Increase the number of subdivided polygons (the artifacts will become smaller).
  2. Give the object some thickness so that it is not a single sheet of polygons.

'Hardware texturing' with the Ai Sky and Ai SkyDome light

Hardware texturing in Maya's viewport will only work when using a Maya file texture with either the Ai Sky or Ai Skydome light. Using an 'Ai Image', for example, will return black in the viewport.

Ai Sky UV mapping is reversed

A ramp texture that is set to the U direction will render incorrectly when connected to the Ai Sky. This can be corrected by scaling the Ai Sky -1 in Z and setting 'Facing' to 'back'.

Tx files and Viewport 2.0

Note that MtoA uses a texture resolution of 1024 when reading .tx files. If a larger resolution is required, you will need to enable "Maximum Texture Resolution Clamping" in the Viewport 2.0 settings and adjust the "Max Texture Resolution".