bullet-featherstone: Fix finding free group for a body with fixed base (#700)

Signed-off-by: Ian Chen <ichen@openrobotics.org>

Author: iche033

bullet-featherstone/src/FreeGroupFeatures.cc

@@ -85,37 +85,39 @@ Identity FreeGroupFeatures::FindFreeGroupForModel(
 {
   const auto *model = this->ReferenceInterface<ModelInfo>(_modelID);
 
-  // Reject if the model has fixed base
-  if (model->body->hasFixedBase())
-    return this->GenerateInvalidId();
-
-  // Also reject if the model is a child of a fixed constraint
-  // (detachable joint)
   for (const auto & joint : this->joints)
   {
+    // Also reject if the model is a child of a fixed constraint
+    // (detachable joint)
     if (joint.second->fixedConstraint)
     {
       if (joint.second->fixedConstraint->getMultiBodyB() == model->body.get())
       {
         return this->GenerateInvalidId();
       }
     }
+    // Reject if the model has a world joint
+    if (std::size_t(joint.second->model) == std::size_t(_modelID))
+    {
+      const auto *identifier =
+          std::get_if<RootJoint>(&joint.second->identifier);
+      if (identifier)
+      {
+        return this->GenerateInvalidId();
+      }
+    }
   }
 
-
   return _modelID;
 }
 
 /////////////////////////////////////////////////
 Identity FreeGroupFeatures::FindFreeGroupForLink(
     const Identity &_linkID) const
 {
+  // Free groups in bullet-featherstone are currently represented by ModelInfo
   const auto *link = this->ReferenceInterface<LinkInfo>(_linkID);
-  const auto *model = this->ReferenceInterface<ModelInfo>(link->model);
-  if (model->body->hasFixedBase())
-    return this->GenerateInvalidId();
-
-  return link->model;
+  return this->FindFreeGroupForModel(link->model);
 }
 
 /////////////////////////////////////////////////

test/common_test/free_joint_features.cc

@@ -316,6 +316,121 @@ TEST_F(FreeGroupFeaturesTest, FreeGroupSetWorldPosePrincipalAxesOffset)
   }
 }
 
+TEST_F(FreeGroupFeaturesTest, FreeGroupSetWorldPoseStaticAndFixedModel)
+{
+  const std::string modelStaticStr = R"(
+    <sdf version="1.11">
+      <model name="sphere">
+        <static>true</static>
+        <pose>1 2 3.0 0 0 0</pose>
+        <link name="link">
+          <collision name="coll_sphere">
+            <geometry>
+              <sphere>
+                <radius>0.1</radius>
+              </sphere>
+            </geometry>
+          </collision>
+        </link>
+      </model>
+    </sdf>)";
+
+  const std::string modelWorldFixedStr = R"(
+    <sdf version="1.11">
+      <model name="sphere_world_fixed">
+        <static>false</static>
+        <pose>3 2 3.0 0 0 0</pose>
+        <link name="link">
+          <collision name="coll_sphere">
+            <geometry>
+              <sphere>
+                <radius>0.1</radius>
+              </sphere>
+            </geometry>
+          </collision>
+        </link>
+        <joint name="world_fixed" type="fixed">
+          <parent>world</parent>
+          <child>link</child>
+        </joint>
+      </model>
+    </sdf>)";
+
+  for (const std::string &name : pluginNames)
+  {
+    std::cout << "Testing plugin: " << name << std::endl;
+    gz::plugin::PluginPtr plugin = loader.Instantiate(name);
+
+    auto engine = gz::physics::RequestEngine3d<TestFeatureList>::From(plugin);
+    ASSERT_NE(nullptr, engine);
+
+    sdf::Root root;
+    sdf::Errors errors = root.Load(
+      common_test::worlds::kGroundSdf);
+    EXPECT_EQ(0u, errors.size()) << errors;
+
+    EXPECT_EQ(1u, root.WorldCount());
+    const sdf::World *sdfWorld = root.WorldByIndex(0);
+    ASSERT_NE(nullptr, sdfWorld);
+
+    auto world = engine->ConstructWorld(*sdfWorld);
+    ASSERT_NE(nullptr, world);
+
+    // create the static model
+    errors = root.LoadSdfString(modelStaticStr);
+    ASSERT_TRUE(errors.empty()) << errors;
+    ASSERT_NE(nullptr, root.Model());
+    world->ConstructModel(*root.Model());
+
+    auto modelStatic = world->GetModel("sphere");
+    ASSERT_NE(nullptr, modelStatic);
+    auto link = modelStatic->GetLink("link");
+    ASSERT_NE(nullptr, link);
+    auto frameDataLink = link->FrameDataRelativeToWorld();
+    EXPECT_EQ(gz::math::Pose3d(1, 2, 3, 0, 0, 0),
+              gz::math::eigen3::convert(frameDataLink.pose));
+
+    // get free group and set new pose
+    auto freeGroup = modelStatic->FindFreeGroup();
+    ASSERT_NE(nullptr, freeGroup);
+    gz::math::Pose3d newPose(4, 5, 6, 0, 0, 1.57);
+    freeGroup->SetWorldPose(
+        gz::math::eigen3::convert(newPose));
+    frameDataLink = link->FrameDataRelativeToWorld();
+    // static model should move to new pose
+    EXPECT_EQ(newPose,
+              gz::math::eigen3::convert(frameDataLink.pose));
+
+    // create the model with world joint
+    errors = root.LoadSdfString(modelWorldFixedStr);
+    ASSERT_TRUE(errors.empty()) << errors;
+    ASSERT_NE(nullptr, root.Model());
+    world->ConstructModel(*root.Model());
+
+    auto modelFixed = world->GetModel("sphere_world_fixed");
+    ASSERT_NE(nullptr, modelFixed);
+    link = modelFixed->GetLink("link");
+    ASSERT_NE(nullptr, link);
+    frameDataLink = link->FrameDataRelativeToWorld();
+    gz::math::Pose3d origPose(3, 2, 3, 0, 0, 0);
+    EXPECT_EQ(origPose,
+              gz::math::eigen3::convert(frameDataLink.pose));
+
+    // get free group and set new pose
+    freeGroup = modelFixed->FindFreeGroup();
+    ASSERT_NE(nullptr, freeGroup);
+    freeGroup->SetWorldPose(
+        gz::math::eigen3::convert(newPose));
+    frameDataLink = link->FrameDataRelativeToWorld();
+    // world fixed model should not be able to move to new pose
+    if (this->PhysicsEngineName(name) != "tpe")
+    {
+      EXPECT_EQ(origPose,
+                gz::math::eigen3::convert(frameDataLink.pose));
+    }
+  }
+}
+
 int main(int argc, char *argv[])
 {
   ::testing::InitGoogleTest(&argc, argv);