notes on using blender custom properties to define ad hoc glTF node extras

[humbletim]

1. Stock Blender lets you attach arbitrary custom properties to objects:

2. Once defined, those properties show up (and can be adjusted) right within information panel:

3. During glTF export there is an "Include Custom Properties" option:

4. Custom properties are reflected as extras on the glTF node:

{
    "asset" : {
        "generator" : "Khronos glTF Blender I/O v1.5.17",
        "version" : "2.0"
    },
    "scene" : 0,
    "scenes" : [ {
            "name" : "Scene",
            "nodes" : [ 0, 1, 2 ]
        } ],
    "nodes" : [
        {
+            "extras" : {
+                "prop" : 1
+            }, 
            "mesh" : 0,
            "name" : "Cube"
        },
        {
            "name" : "Light", 
            "...": "..."
        }
  ]
}