Fix multi output nodes

[RichardFrangenberg]

fixes multioutput nodes like "separate".
fixes #34

[manuelkoester]

I am still getting MaterialX validation warnings on this, but it does seem to work 🤔

<?xml version="1.0"?>
<materialx version="1.38">
  <nodegraph name="NG_main">
    <separate3 name="Separate3" type="multioutput" xpos="-10.946125018131086" ypos="-0.35007962180986196">
      <input name="in" type="color3" value="0, 0, 0" nodename="Constant" />
      <output name="outr" type="float" />
      <output name="outg" type="float" />
      <output name="outb" type="float" />
    </separate3>
    <constant name="Constant" type="color3" xpos="-13.843008149741326" ypos="-0.31585167668387043">
      <input name="value" type="color3" value="1, 0, 0.015686" />
      <output name="out" type="color3" />
    </constant>
    <combine3 name="Combine3" type="color3" xpos="-6.069929920631035" ypos="-0.3098670317401928">
      <input name="in1" type="float" value="0" output="outr" nodename="Separate3" />
      <input name="in2" type="float" value="0" output="outg" nodename="Separate3" />
      <input name="in3" type="float" value="0" output="outb" nodename="Separate3" />
      <output name="out" type="color3" />
    </combine3>
    <output name="output_Combine3_out" type="color3" nodename="Combine3" />
  </nodegraph>
  <surfacematerial name="USD_Default" type="material" xpos="2.2925" ypos="0.0">
    <input name="surfaceshader" type="surfaceshader" nodename="Standard_surface" />
    <output name="out" type="material" />
  </surfacematerial>
  <standard_surface name="Standard_surface" type="surfaceshader" xpos="-1.6725" ypos="0.0">
    <input name="base" type="float" value="1" />
    <input name="base_color" type="color3" value="1, 1, 1" nodegraph="NG_main" output="output_Combine3_out" />
    <input name="diffuse_roughness" type="float" value="0" />
    <input name="metalness" type="float" value="0.8" />
    <input name="specular" type="float" value="1" />
    <input name="specular_color" type="color3" value="1, 1, 1" />
    <input name="specular_roughness" type="float" value="0.1" />
    <input name="specular_IOR" type="float" value="1.5" />
    <input name="specular_anisotropy" type="float" value="0" />
    <input name="specular_rotation" type="float" value="0" />
    <input name="transmission" type="float" value="0" />
    <input name="transmission_color" type="color3" value="1, 1, 1" />
    <input name="transmission_depth" type="float" value="0" />
    <input name="transmission_scatter" type="color3" value="0, 0, 0" />
    <input name="transmission_scatter_anisotropy" type="float" value="0" />
    <input name="transmission_dispersion" type="float" value="0" />
    <input name="transmission_extra_roughness" type="float" value="0" />
    <input name="subsurface" type="float" value="0" />
    <input name="subsurface_color" type="color3" value="1, 1, 1" />
    <input name="subsurface_radius" type="color3" value="1, 1, 1" />
    <input name="subsurface_scale" type="float" value="1" />
    <input name="subsurface_anisotropy" type="float" value="0" />
    <input name="sheen" type="float" value="0" />
    <input name="sheen_color" type="color3" value="1, 1, 1" />
    <input name="sheen_roughness" type="float" value="0.3" />
    <input name="coat" type="float" value="1" />
    <input name="coat_color" type="color3" value="0.6, 0.45, 1" />
    <input name="coat_roughness" type="float" value="0.1" />
    <input name="coat_anisotropy" type="float" value="0" />
    <input name="coat_rotation" type="float" value="0" />
    <input name="coat_IOR" type="float" value="2.5" />
    <input name="coat_affect_color" type="float" value="0" />
    <input name="coat_affect_roughness" type="float" value="0" />
    <input name="thin_film_thickness" type="float" value="0" />
    <input name="thin_film_IOR" type="float" value="1.5" />
    <input name="emission" type="float" value="0" />
    <input name="emission_color" type="color3" value="1, 1, 1" />
    <input name="opacity" type="color3" value="1, 1, 1" />
    <input name="thin_walled" type="boolean" value="false" />
    <output name="out" type="surfaceshader" />
  </standard_surface>
</materialx>

Is this a problem on our side or MaterialX?

[manuelkoester]

Is this a problem on our side or MaterialX?

Seems to be a MaterialX thing. Let's ping Bernard if he could raise this internally. Will merge