Add compound triggers to KHR_physics_rigid_bodies

extensions/2.0/Khronos/KHR_physics_rigid_bodies/README.md

@@ -133,9 +133,17 @@ Note, that this can generate asymmetric states - `A` might determine that it _do
 
 ### Triggers
 
-A useful construct in a physics engine is a collision volume which does not generate impulses when overlapping with other volumes - implementations may use this behavior to generate events, which can implement application-specific logic; such objects are typically called "triggers", "phantoms", "sensors", or "overlap volumes" in physics simulation engines.
+A useful construct in a physics engine is a collision volume which does not generate impulses when overlapping with other volumes. Triggers allow specifying such volumes either as a single shape or combination of shapes.
 
-A node may have a `trigger` property set; this is similar to the `collider` in that it references a collision volume defined by the `KHR_collision_shapes` extension but lacks a physics material. It does, however, provide a collision filter with the same semantics as the `collider`.
+Implementations may use these objects as sensors which generate events and can be used to trigger application-specific logic. These objects are typically called "triggers", "sensors", "phantoms", or "overlap volumes" in physics simulation engines.
+
+A node may have a `trigger` property set, which is similar to the `collider` property. Both have a `shape` property that references a geometric shape defined by the `KHR_collision_shapes` extension, and both provide a collision filter with the same semantics. However, the `trigger` property lacks a physics material. Alternatively, a `trigger` may have a `nodes` property, which is an array of descendant glTF nodes with a trigger property, which make up a compound trigger on this glTF node.
+
+| |Type|Description|
+| - | - | -|
+|**shape**|`integer`| The index of a top level `Shape`, which provides the geometry of the trigger.|
+|**nodes**|`[integer]`|For compound triggers, the set of descendant glTF nodes with a trigger property that make up this compound trigger.|
+|**collisionFilter**|`integer`|Indexes into the top level `collisionFilters` and describes a filter which determines if this collider should perform collision detection against another collider.|
 
 Describing the precise mechanism by which overlap events are generated and what occurs as a result is beyond the scope of this specification; simulation software will typically output overlap begin/end events as an output from the simulation step, which is hooked into application-specific business logic.
 

extensions/2.0/Khronos/KHR_physics_rigid_bodies/schema/node.KHR_physics_rigid_bodies.trigger.schema.json

@@ -3,20 +3,41 @@
     "title": "KHR_physics_rigid_bodies Node Trigger Property",
     "type": "object",
     "description": "Parameters describing a volume used for collison detection, but does not cause a collision response.",
-    "allOf": [ { "$ref": "glTFProperty.schema.json" } ],
+    "allOf": [{ "$ref": "glTFProperty.schema.json" }],
     "properties": {
         "shape": {
-            "allOf": [ { "$ref": "glTFid.schema.json" } ],
+            "allOf": [{ "$ref": "glTFid.schema.json" }],
             "description": "The index of the shape in the top level shapes array."
         },
+        "nodes": {
+            "type": "array",
+            "description": "For compound triggers, the set of descendant glTF nodes with a trigger property that make up this compound trigger.",
+            "items": {
+                "$ref": "glTFid.schema.json"
+            },
+            "uniqueItems": true,
+            "minItems": 1
+        },
         "collisionFilter": {
-            "allOf": [ { "$ref": "glTFid.schema.json" } ],
+            "allOf": [{ "$ref": "glTFid.schema.json" }],
             "description": "The index of the filter information in the top level collisionFilters array."
         },
         "extensions": { },
         "extras": { }
     },
-    "required": [
-        "shape"
+    "anyOf": [
+        {
+            "allOf": [
+                { "required": ["shape"] },
+                { "not": { "required": ["nodes"] } }
+            ]
+        },
+        {
+            "allOf": [
+                { "required": ["nodes"] },
+                { "not": { "required": ["shape"] } },
+                { "not": { "required": ["collisionFilter"] } }
+            ]
+        }
     ]
 }