Address comments

omnigibson/prims/geom_prim.py

@@ -51,6 +51,10 @@ def _post_load(self):
         super()._post_load()
 
         # Temporarily set the opacity threshold to be 0.1. This will be automated in later exports.
+        # We do this because in previous exports we included continuous alpha values for opacity
+        # but the ray tracing renderer can only handle binary opacity values. The default threshold
+        # leaves most objects entirely transparent, so we try to avoid that here.
+        # TODO: Remove this after the next dataset export
         if self.material:
             self.material.opacity_threshold = 0.1
 

omnigibson/prims/rigid_prim.py

@@ -825,6 +825,14 @@ def meta_link_type(self):
 
     @cached_property
     def meta_link_id(self):
+        """The meta link id of this link, if the link is a meta link.
+
+        The meta link ID is a semantic identifier for the meta link within the meta link type. It is
+        used when an object has multiple meta links of the same type. It can be just a numerical index,
+        or for some objects, it will be a string that can be matched to other meta links. For example,
+        a stove might have toggle buttons named "left" and "right", and heat sources named "left" and
+        "right". The meta link ID can be used to match the toggle button to the heat source.
+        """
         assert self.is_meta_link, f"{self.name} is not a meta link"
         if self.prim.HasAttribute("ig:metaLinkId"):
             return self.get_attribute("ig:metaLinkId")
@@ -835,6 +843,12 @@ def meta_link_id(self):
 
     @cached_property
     def meta_link_sub_id(self):
+        """The integer meta link sub id of this link, if the link is a meta link.
+
+        The meta link sub ID identifies this link as one of the parts of a meta link. For example, an
+        attachment meta link's ID will be the attachment pair name, and each attachment point that
+        works with that pair will show up as a separate link with a unique sub ID.
+        """
         assert self.is_meta_link, f"{self.name} is not a meta link"
         if self.prim.HasAttribute("ig:metaLinkSubId"):
             return int(self.get_attribute("ig:metaLinkSubId"))

omnigibson/utils/asset_conversion_utils.py

@@ -287,6 +287,10 @@ def _set_mtl_opacity(mtl_prim, texture):
     # This defaults to some other value, which takes opaque black channels in the
     # image to be fully transparent. This is not what we want.
     lazy.omni.usd.create_material_input(mtl_prim, "opacity_mode", 0, lazy.pxr.Sdf.ValueTypeNames.Int)
+
+    # We also need to set an opacity threshold. Our objects can include continuous alpha values for opacity
+    # but the ray tracing renderer can only handle binary opacity values. The default threshold
+    # leaves most objects entirely transparent, so we try to avoid that here.
     lazy.omni.usd.create_material_input(mtl_prim, "opacity_threshold", 0.1, lazy.pxr.Sdf.ValueTypeNames.Float)
 
     # Verify it was set