Remove distance constraints.

- `distance` constraints were not very useful and increased the contact buffer within the constraint solver, violating a core design principle. Therefore they have been removed.
- The enum value `mjEQ_DISTANCE` is retained, but errors will be thrown in the parser and engine if these constraints are selected.

PiperOrigin-RevId: 467050101
Change-Id: Ie72a07e4fe338eea5107004a9fc0f5e47eb0c3b7

unity/Runtime/Components/Equality/MjDistance.cs

@@ -1,48 +0,0 @@
-// Copyright 2019 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.
-
-using System;
-using System.Linq;
-using System.Xml;
-using UnityEngine;
-
-namespace Mujoco {
-
-  public class MjDistance : MjBaseConstraint {
-    public MjGeom Geom1;
-    public MjGeom Geom2;
-    protected override string _constraintName => "distance";
-
-    protected override void FromMjcf(XmlElement mjcf) {
-      Geom1 = mjcf.GetObjectReferenceAttribute<MjGeom>("geom1");
-      Geom2 = mjcf.GetObjectReferenceAttribute<MjGeom>("geom2");
-    }
-
-    protected override void ToMjcf(XmlElement mjcf) {
-      if (Geom1 == null || Geom2 == null) {
-        throw new NullReferenceException($"Both geoms in distance {name} must be assigned.");
-      }
-
-      mjcf.SetAttribute("geom1", Geom1.MujocoName);
-      mjcf.SetAttribute("geom2", Geom2.MujocoName);
-    }
-
-    public void OnValidate() {
-      if (Geom1 != null && Geom1 == Geom2) {
-        Debug.LogError("Geom1 and Geom2 can't be the same - resetting Geom2.", this);
-        Geom2 = null;
-      }
-    }
-  }
-}

unity/Runtime/Components/Equality/MjDistance.cs.meta

@@ -1,13 +0,0 @@
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-timeCreated: 1552309644
-licenseType: Pro
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unity/Runtime/Importer/MjcfImporter.cs

@@ -296,9 +296,6 @@ public class MjcfImporter {
       case "tendon":
         equalityType = typeof(MjTendonConstraint);
         break;
-      case "distance":
-        equalityType = typeof(MjDistance);
-        break;
       default:
         Debug.Log($"The importer does not yet support equality <{node.Name}>.");
         break;

unity/Tests/Editor/Components/Equality/MjDistanceTests.cs

@@ -1,74 +0,0 @@
-// Copyright 2019 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.
-
-using System;
-using System.Collections;
-using System.Collections.Generic;
-using System.Xml;
-using NUnit.Framework;
-using UnityEngine;
-
-namespace Mujoco {
-  [TestFixture]
-  public class MjDistanceTests {
-    private MjGeom _geom1;
-    private MjGeom _geom2;
-    private MjDistance _distance;
-    private XmlDocument _doc;
-
-    [SetUp]
-    public void SetUp() {
-      _geom1 = new GameObject("geom1").AddComponent<MjGeom>();
-      _geom2 = new GameObject("geom2").AddComponent<MjGeom>();
-      _distance = new GameObject("distance").AddComponent<MjDistance>();
-      _doc = new XmlDocument();
-    }
-
-    [TearDown]
-    public void TearDown() {
-      UnityEngine.Object.DestroyImmediate(_distance.gameObject);
-      UnityEngine.Object.DestroyImmediate(_geom1.gameObject);
-      UnityEngine.Object.DestroyImmediate(_geom2.gameObject);
-    }
-
-    [Test]
-    public void ErrorThrownWhenGeom1Empty() {
-      // This is an illegal MJCF, but the purpose of this test is to verify that if
-      // the user didn't assign the geom in the editor, an error will be thrown when play is hit.
-      _doc.LoadXml("<geom/>");
-      _distance.ParseMjcf(_doc.GetElementsByTagName("geom")[0] as XmlElement);
-      Assert.That(() => { _distance.GenerateMjcf("name", _doc); }, Throws.Exception);
-    }
-
-    // In this constraint both elements are required.
-    [Test]
-    public void ErrorThrownWhenGeom2Empty() {
-      _doc.LoadXml("<geom geom1='geom1'/>");
-      _distance.ParseMjcf(_doc.GetElementsByTagName("geom")[0] as XmlElement);
-      Assert.That(() => { _distance.GenerateMjcf("name", _doc); }, Throws.Exception);
-    }
-
-    [Test]
-    public void ParseAndGenerate() {
-      _doc.LoadXml("<distance geom1='geom1' geom2='geom2'/>");
-      _distance.ParseMjcf(_doc.GetElementsByTagName("distance")[0] as XmlElement);
-      Assert.That(_distance.Geom1, Is.EqualTo(_geom1));
-      Assert.That(_distance.Geom2, Is.EqualTo(_geom2));
-      var mjcf = _distance.GenerateMjcf("name", _doc);
-      Assert.That(mjcf.OuterXml, Does.Contain("<distance"));
-      Assert.That(mjcf.OuterXml, Does.Contain("geom1=\""));
-      Assert.That(mjcf.OuterXml, Does.Contain("geom2=\""));
-    }
-  }
-}

unity/Tests/Editor/Components/Equality/MjDistanceTests.cs.meta

@@ -1,13 +0,0 @@
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