Material isn't getting applied about materialx

[numega]

The OpenGL error is due to GlslProgram::unbindGeometry() being called for each assignment of the material. You can reproduce this issue with the shaderball.obj file in resources/Geometry. As a workaround I added the following at the beginning of the function:

void GlslProgram::unbindGeometry()
{
    if (_vertexArray == GlslProgram::UNDEFINED_OPENGL_RESOURCE_ID)
        return;

    glBindVertexArray(_vertexArray);

[bernardkwok]

What you have should show up green without modification.

From an initial look, it appears to be an issue with having the <surfacematerial> in the nodegraph definition not picking up the default values properly for code generation.

For example this does pick up default values properly:

<?xml version="1.0"?>
<materialx version="1.38" colorspace="lin_rec709">
  <nodedef name="NG_mymaterial" node="mymaterial">
    <input name="colorA" type="color3" value="0, 0.5, 0" />
    <input name="colorB" type="color3" value="0, 0.5, 0" />
    <output name="out" type="surfaceshader" />
  </nodedef>
  <nodegraph name="blah" nodedef="NG_mymaterial" >
    <add name="add1" type="color3" nodedef="ND_add_color3">
      <input name="in1" type="color3" interfacename="colorA" />
      <input name="in2" type="color3" interfacename="colorB" />
    </add>
    <UsdPreviewSurface name="SR_default" type="surfaceshader">
        <input name="diffuseColor" type="color3" nodename="add1"/>
    </UsdPreviewSurface>
    <output name="out" type="surfaceshader" nodename="SR_default" />
  </nodegraph>
  <mymaterial name="Material1" type="surfaceshader" />
  <output name="test" nodename="Material1" type="surfaceshader" />
</materialx>

[niklasharrysson]

Just some more info from debugging this:

The problem is that when finding renderable elements in a document, for materials we dig into it and extract the surfaceshader connected inside/upstream. So in this case we extract the UsdPreviewSurface from inside the materials implementation graph and generate code for that. The problem is that we then lose all information about what is connected or set on the materials interface.

So we need to treat materials as renderable elements explicitly, without extracting their shaders. And as part of this we need to add support for code generation of material elements, including having materials implemented as graphs.

[jstone-lucasfilm]

Thanks for this original report, @numega, and thanks to @niklasharrysson for addressing it in #981!