Particles with arbitrary geoms and joints.

Fixes #553

PiperOrigin-RevId: 486614769
Change-Id: I9a09bf73da97b6b9746800a72ac6c97cce2efa92

test/user/CMakeLists.txt

@@ -20,3 +20,6 @@ target_link_libraries(user_objects_test fixture gmock)
 
 mujoco_test(user_mesh_test)
 target_link_libraries(user_mesh_test fixture gmock absl::str_format)
+
+mujoco_test(user_composite_test)
+target_link_libraries(user_composite_test fixture gmock)

test/user/user_composite_test.cc

@@ -0,0 +1,80 @@
+// Copyright 2021 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Tests for user/user_model.cc.
+
+#include <cstddef>
+#include <string>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <absl/strings/str_format.h>
+#include <mujoco/mjmodel.h>
+#include <mujoco/mujoco.h>
+#include "test/fixture.h"
+
+namespace mujoco {
+namespace {
+
+using ::testing::IsNull;
+using ::testing::NotNull;
+using ::testing::HasSubstr;
+using UserCompositeTest = MujocoTest;
+
+// ------------- test automatic inference of nuser_xxx -------------------------
+
+TEST_F(UserCompositeTest, MultipleJointsNotAllowedUnlessParticle) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+  <worldbody>
+    <body>
+      <freejoint/>
+      <composite type="box" count="7 7 7" spacing="0.04">
+        <joint kind="main" solreffix="0.03 1" solimpfix="0 .1 .01"/>
+        <joint kind="main" solreffix="0.03 1" solimpfix="0 .1 .01"/>
+      </composite>
+    </body>
+  </worldbody>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* m = LoadModelFromString(xml, error.data(), error.size());
+  EXPECT_THAT(m, IsNull());
+  EXPECT_THAT(error.data(), HasSubstr("Only particles are allowed to have multiple joints"));
+}
+
+TEST_F(UserCompositeTest, StretchAndTwistAllowed) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+  <worldbody>
+    <body name="B10">
+      <freejoint/>
+      <composite type="rope" count="21 1 1" spacing="0.04">
+        <joint kind="main" damping="0.005"/>
+        <joint kind="stretch" damping="0.005"/>
+        <joint kind="twist" damping="0.005"/>
+        <geom type="capsule" size=".01 .015"/>
+      </composite>
+    </body>
+  </worldbody>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* m = LoadModelFromString(xml, error.data(), error.size());
+  EXPECT_THAT(m, NotNull());
+  mj_deleteModel(m);
+}
+
+}  // namespace
+}  // namespace mujoco