For example, can I transfer Arnold shaders from 3ds Max to Maya? Or from Houdini to Maya?
The answer is no. The Arnold plugins don’t include code for reading shader nodes from an ASS file and creating shader trees inside the host application (eg Maya, Houdini, or Cinema 4D).
You can use ASS files to take shapes and shaders from one app and render them in another app, but those shapes and shaders are never created inside the other app.
An MtoA Standin (aka an Arnold Procedural in HtoA and C4DtoA) references an ASS file, and passes that on to Arnold at render time.
The ASS file contains Arnold nodes (shapes and shaders). Those Arnold nodes are not created inside the 3D application.
Instead, the standin node is translated to an Arnold procedural node, and at render time, that procedural node is expanded, and all the Arnold shapes and shaders are created inside the Arnold scene.
There’s an Arnold error that recommends setting the load_at_init parameter, but people don’t always know where to find that in their favorite Arnold plugin.
ERROR| [proc] c4d|Arnold_Procedural: bounds supplied to procedural node are not large enough to contain the actual underlying geometry.
Replace given bounds: (-1, -1, -1) X (1, 1, 1), with: (-9.4028616, -9.43616867, -9.21633244) X (9.3304739, 9.43616867, 9.21633244).
Setting the procedural's load_at_init parameter to true would also fix this.
The load_at_init parameter controls whether the procedural (standin) is loaded during scene intialization (before rendering starts), or during rendering (when a ray hits the procedural bounding box).
By default, load_at_init is false, which means that procedural loading is deferred until render time.
And so, in MtoA, C4DtoA, and SItoA, the load_at_init parameter is exposed as Defer Standin Load, which is enabled by default. In HtoA, you have a Load At Init parameter on for the Arnold Procedural node.