Retrieve default shader input from shader node

omnigibson/prims/material_prim.py

@@ -70,6 +70,7 @@ def __init__(
     ):
         # Other values that will be filled in at runtime
         self._shader = None
+        self._shader_node = None
 
         # Users of this material: should be a set of BaseObject and BaseSystem
         self._users = set()
@@ -148,6 +149,7 @@ def _post_load(self):
 
         # Generate shader reference
         self._shader = lazy.omni.usd.get_shader_from_material(self._prim)
+        self._shader_node = lazy.usd.mdl.RegistryUtils.GetShaderNodeForPrim(self._shader.GetPrim())
 
     def bind(self, target_prim_path):
         """
@@ -216,7 +218,11 @@ def get_input(self, inp):
         Returns:
             any: value of the requested @inp
         """
-        return self._shader.GetInput(inp).Get()
+        non_default_inp = self._shader.GetInput(inp).Get()
+        if non_default_inp is not None:
+            return non_default_inp
+
+        return self._shader_node.GetInput(inp).GetDefaultValue()
 
     def set_input(self, inp, val):
         """

omnigibson/systems/micro_particle_system.py

@@ -494,9 +494,6 @@ def initialize(self, scene):
         self.system_prim = self._create_particle_system()
         # Get material
         material = self._get_particle_material_template()
-        # Load the material if it's newly created and has never been loaded before
-        if not material.loaded:
-            material.load()
         material.add_user(self)
         self._material = material
         # Bind the material to the particle system (for isosurface) and the prototypes (for non-isosurface)