Add checking for implicit outputs on multioutput nodes on load

[kwokcb]

Issue

A node may not have all of it's outputs explicitly specified. If an output connection is specified on a MaterialX node and
the output is not found on the upstream node then a connection will not be made. This affects load.

If you create a node and make a connection then this will not occur since the qx_node populates itself with all the required outputs from the node definition.

Change

To perform the same action on the mx_node as the qx_node, some additional logic has been added to add input any missing outputs. This is for now only for multioutput nodes as this appears to be the failing case. Note that this does not add any additional information not already added on save from the qx_node.

Test

This is an example glTF imported material. In this case gltf_colorimage does not have it's outputs specified so will fail connection before this change.

<?xml version="1.0"?>
<materialx version="1.39">
  <gltf_pbr name="SciFiHelmet" type="surfaceshader">
    <input name="base_color" type="color3" nodename="image_base_color" output="outcolor" />
    <input name="metallic" type="float" nodename="extract_orm3" />
    <input name="roughness" type="float" nodename="extract_orm2" />
    <input name="occlusion" type="float" nodename="image_occlusion" />
    <input name="normal" type="vector3" nodename="image_normal" />
    <input name="emissive" type="color3" value="0, 0, 0" colorspace="srgb_texture" />
  </gltf_pbr>
  <surfacematerial name="MAT_SciFiHelmet" type="material" xpos="17.391304" ypos="0.000000">
    <input name="surfaceshader" type="surfaceshader" nodename="SciFiHelmet" />
  </surfacematerial>
  <gltf_colorimage name="image_base_color" type="multioutput" xpos="10.144928" ypos="-2.948276">
    <input name="file" type="filename" value="SciFiHelmet_BaseColor.png" colorspace="srgb_texture" fileprefix="" />
  </gltf_colorimage>
  <gltf_image name="image_orm" type="vector3" xpos="6.521739" ypos="6.465517">
    <input name="file" type="filename" value="SciFiHelmet_MetallicRoughness.png" fileprefix="" />
  </gltf_image>
  <extract name="extract_orm" type="float" xpos="9.753623" ypos="5.387931">
    <input name="in" type="vector3" nodename="image_orm" />
    <input name="index" type="integer" value="0" />
  </extract>
  <extract name="extract_orm2" type="float" xpos="10.144928" ypos="0.327586">
    <input name="in" type="vector3" nodename="image_orm" />
    <input name="index" type="integer" value="1" />
  </extract>
  <extract name="extract_orm3" type="float" xpos="10.144928" ypos="-1.310345">
    <input name="in" type="vector3" nodename="image_orm" />
    <input name="index" type="integer" value="2" />
  </extract>
  <gltf_normalmap name="image_normal" type="vector3" xpos="10.144928" ypos="1.956897">
    <input name="file" type="filename" value="SciFiHelmet_Normal.png" fileprefix="" />
  </gltf_normalmap>
  <gltf_image name="image_occlusion" type="float" xpos="10.144928" ypos="3.293103">
    <input name="file" type="filename" value="SciFiHelmet_AmbientOcclusion.png" fileprefix="" />
  </gltf_image>
  <look name="look">
    <materialassign name="MAT_SciFiHelmet" material="MAT_SciFiHelmet" geom="/SciFiHelmet/SciFiHelmet" />
  </look>
</materialx>

This is a snapshot after the fix (with the appropriate base_color connection being made.

Note: The error showing up is not due to this issue but it seems the "auto nodegraph" creation is creating invalid nodegraph outputs. Turing this off removes this error.

[manuelkoester]

Awesome Bernard, thank you for your work.
I left some comments about mostly cosmetical things, please let me know if you would like to adjust them, otherwise I would merge and leave it be :)

[manuelkoester]

Could we potentially rename this to something like complete_outputs_for_multioutputs or something along those lines?