From e050f36b5afc78cd9550a563e28a3e9573830606 Mon Sep 17 00:00:00 2001
From: Alessio Quaglino <quaglino@google.com>
Date: Thu, 9 Jun 2022 08:03:04 -0700
Subject: [PATCH] Write sensor `reftype` and `refname` (if present) to XML
 file.

PiperOrigin-RevId: 453926332
Change-Id: I61f4aa2dc6186149b22af71eb8bb0fb2ffd84209
---
 src/xml/xml_native_writer.cc | 6 ++++++
 test/testdata/model.xml      | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/xml/xml_native_writer.cc b/src/xml/xml_native_writer.cc
index 1b55e4dd..9d0926c2 100644
--- a/src/xml/xml_native_writer.cc
+++ b/src/xml/xml_native_writer.cc
@@ -1559,6 +1559,12 @@ void mjXWriter::Sensor(XMLElement* root) {
     WriteAttr(elem, "cutoff", 1, &psen->cutoff, &zero);
     WriteAttr(elem, "noise", 1, &psen->noise, &zero);
     WriteVector(elem, "user", psen->userdata);
+
+    // add reference if present
+    if (psen->reftype > 0) {
+      WriteAttrTxt(elem, "reftype", mju_type2Str(psen->reftype));
+      WriteAttrTxt(elem, "refname", psen->refname);
+    }
   }
 
   // remove section if empty
diff --git a/test/testdata/model.xml b/test/testdata/model.xml
index fbf9d079..52913b50 100644
--- a/test/testdata/model.xml
+++ b/test/testdata/model.xml
@@ -121,7 +121,7 @@
     <general joint="wheel_1" biastype="affine" dyntype="integrator" dynprm="1" biasprm="0 -1"/>
   </actuator>
   <sensor>
-    <framepos objtype="site" objname="wheel_0"/>
+    <framepos objtype="site" objname="wheel_0" reftype="site" refname="wheel_2"/>
     <rangefinder site="rf"/>
     <gyro site="wheel_2"/>
     <touch site="wheel_1"/>