MM Scene Graph - Test input-only attribute connections.

Nodes can share attributes, essentially meaning that connections between
attributes can be supported, as long as the values are shared and no
computations are required 'between' the attributes.

mmscenegraph/rust/src/scene/graph.rs

@@ -645,4 +645,54 @@ mod tests {
 
         assert_eq!(sg.num_transform_nodes(), 3);
     }
+
+    // Creates two transform nodes that both share the same translateY
+    // value - AKA, it's a connection from one attribute to the other
+    // so both share the same value.
+    #[test]
+    fn test_create_input_only_attr_connection() {
+        let mut sg = SceneGraph::new();
+        let mut attrdb = AttrDataBlock::new();
+        assert_eq!(sg.num_transform_nodes(), 0);
+
+        let rotate_order = RotateOrder::XYZ;
+        let tfm_a = create_static_transform(
+            &mut sg,
+            &mut attrdb,
+            (0.0, 42.0, 0.0),
+            (0.0, 0.0, 0.0),
+            (1.0, 1.0, 1.0),
+            rotate_order,
+        );
+
+        let (tx, _ty, tz) = (42.0, 0.0, 0.0);
+        let attr_tx = attrdb.create_attr_static(tx);
+        // Connection from tfm_a.ty to tfm_b.ty.
+        let attr_ty = tfm_a.get_attr_ty();
+        let attr_tz = attrdb.create_attr_static(tz);
+        let translate_attrs = (attr_tx, attr_ty, attr_tz);
+
+        let (rx, ry, rz) = (0.0, 0.0, 0.0);
+        let attr_rx = attrdb.create_attr_static(rx);
+        let attr_ry = attrdb.create_attr_static(ry);
+        let attr_rz = attrdb.create_attr_static(rz);
+        let rotate_attrs = (attr_rx, attr_ry, attr_rz);
+
+        let (sx, sy, sz) = (1.0, 1.0, 1.0);
+        let attr_sx = attrdb.create_attr_static(sx);
+        let attr_sy = attrdb.create_attr_static(sy);
+        let attr_sz = attrdb.create_attr_static(sz);
+        let scale_attrs = (attr_sx, attr_sy, attr_sz);
+
+        let tfm_b = sg.create_transform_node(
+            translate_attrs,
+            rotate_attrs,
+            scale_attrs,
+            rotate_order,
+        );
+
+        sg.set_node_parent(tfm_a.get_id(), NodeId::Root);
+        sg.set_node_parent(tfm_b.get_id(), NodeId::Root);
+        assert_eq!(sg.num_transform_nodes(), 2);
+    }
 }