[Python] Linking nodes

There’s been a few questions recently about nodes that look like this in an ASS file:

 name plusMinusAverage2
 operation "sum"
 input3D 2 1 POINT
0 0 0 0 0 0
 input3D[0] file1
 input3D[1] bulge1

That’s the ASS representation of this (in Maya):
On line 6, you have the default values (two POINTs) for input3D. If there was nothing plugged into the input3D, you’d get the points (0,0,0) and (0,0,0).

Here’s an example that shows how to set up the node links for a MayaPlusMinusAverage3D node.

from arnold import *

ass_file = "mayaplusminusaverage.ass"


# Load the mtoa shaders, which include MayaPlusMinusAverage3D

AiASSLoad(ass_file, AI_NODE_ALL)

# Create a MayaPlusMinusAverage3D node
n = AiNode( "MayaPlusMinusAverage3D" )

# Set the name parameter
AiNodeSetStr( n, "name", "plusMinusAverage2" )

# Set the operation parameter
AiNodeSetStr( n, "operation", "sum" )

# input3D is of type POINT[] (an array of POINTs)

# Allocate an array; by default the array is initialized to 0s
a = AiArrayAllocate( 2, 1, AI_TYPE_POINT )
AiNodeSetArray(n, "input3D", a )

# Link input3D to the file and bulge nodes, which are assumed to already exist
f = AiNodeLookUpByName( "file1" )
b = AiNodeLookUpByName( "bulge1" )
AiNodeLink(f, "input3D[0]", n);
AiNodeLink(b, "input3D[1]", n);

AiASSWrite(ass_file, AI_NODE_ALL, False)

Here’s another example. This time, one input3D is set to (0.3, 0.2, 0.4), and the other input3D is linked to a Bulge node.

 name plusMinusAverage3
 operation "sum"
 input3D 2 1 POINT
0.3 0.2 0.4 0 0 0
 input3D[0] file1

And here’s the Python snippet that creates the node and sets up the link:

n = AiNode( "MayaPlusMinusAverage3D" )

b = AiNodeLookUpByName( "bulge1" )

AiNodeSetStr( n, "name", "plusMinusAverage3" )
AiNodeSetStr( n, "operation", "sum" )

a = AiArrayAllocate( 2, 1, AI_TYPE_POINT )
AiArraySetPnt(a, 0, AtPoint( 0.3, 0.2, 0.4 ) )

AiNodeSetArray(n, "input3D", a )

AiNodeLink(b, "input3D[1]", n);

A couple of notes:

  • You can get the type of parameters like input3D with kick:
    kick -l ..\shaders -info MayaPlusMinusAverage3
    node:         MayaPlusMinusAverage3D
    type:         shader
    output:       RGB
    parameters:   3
    filename:     ..\shaders/mtoa_shaders.dll
    Type          Name                              Default
    ------------  --------------------------------  --------------------------------
    ENUM          operation                         sum
    POINT[]       input3D                           (empty)
    STRING        name
  • For the full list of parameter types such as AI_TYPE_POINT, see the “AtParamEntry API” in the Arnold API Reference (or python/arnold/ai_params.py in the Arnold install).

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