Add [SdfLib](https://github.com/UPC-ViRVIG/SdfLib) plugin to first-party SDFs.

The following dependencies are disabled with a cmake patch file.
- Enoki
- OpenMP
- Assimp
- FCPW

PiperOrigin-RevId: 565352386
Change-Id: Icff9de68408e0afa2032bb83b24491fc4e41d181

plugin/sdf/sdflib.h

@@ -0,0 +1,54 @@
+// Copyright 2022 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.
+
+#ifndef MUJOCO_PLUGIN_SDF_SDFLIB_H_
+#define MUJOCO_PLUGIN_SDF_SDFLIB_H_
+
+#include <optional>
+
+#include <SdfLib/utils/Mesh.h>
+#include <SdfLib/OctreeSdf.h>
+#include <mujoco/mjdata.h>
+#include <mujoco/mjmodel.h>
+#include <mujoco/mjtnum.h>
+#include <mujoco/mjvisualize.h>
+#include "sdf.h"
+
+namespace mujoco::plugin::sdf {
+class SdfLib {
+ public:
+  // Creates a new SdfLib instance or returns null on failure.
+  static std::optional<SdfLib> Create(const mjModel* m, mjData* d,
+                                      int instance);
+  SdfLib(SdfLib&&) = default;
+  ~SdfLib() = default;
+
+  void Reset();
+  void Visualize(const mjModel* m, mjData* d, const mjvOption* opt,
+                 mjvScene* scn, int instance);
+  void Compute(const mjModel* m, mjData* d, int instance);
+  mjtNum Distance(const mjtNum point[3]) const;
+  void Gradient(mjtNum grad[3], const mjtNum point[3]) const;
+
+  static void RegisterPlugin();
+
+ private:
+  SdfLib(sdflib::Mesh&& mesh);
+  SdfVisualizer visualizer_;
+  sdflib::OctreeSdf sdf_func_;
+};
+
+}  // namespace mujoco::plugin::sdf
+
+#endif  // MUJOCO_PLUGIN_SDF_SDFLIB_H_