Move OBJ handling to a mjpDecoder.

PiperOrigin-RevId: 875194599 Change-Id: I2cccc683d69a217f1817e70d16bc1815e366d00c
2026-02-25 09:11:54 -08:00
parent abdea379af
commit b907ffedaa
12 changed files with 258 additions and 109 deletions
@@ -0,0 +1,125 @@
+// Copyright 2026 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.
+
+#include <cstring>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include <mujoco/mjplugin.h>
+#include <mujoco/mjspec.h>
+#include <mujoco/mujoco.h>
+#include <tiny_obj_loader.h>
+
+namespace {
+
+mjSpec* Decode(mjResource* resource, const mjVFS* vfs) {
+  const void* bytes = nullptr;
+  int buffer_sz = mju_readResource(resource, &bytes);
+  if (buffer_sz < 0) {
+    mju_warning("obj_decoder: could not read OBJ file '%s'", resource->name);
+    return nullptr;
+  }
+
+  tinyobj::ObjReader obj_reader;
+  const char* buffer = static_cast<const char*>(bytes);
+  obj_reader.ParseFromString(std::string(buffer, buffer_sz), std::string());
+
+  if (!obj_reader.Valid()) {
+    mju_warning("obj_decoder: could not parse OBJ file '%s'", resource->name);
+    return nullptr;
+  }
+
+  mjSpec* spec = mj_makeSpec();
+  mjsMesh* mesh = mjs_addMesh(spec, nullptr);
+
+  const auto& attrib = obj_reader.GetAttrib();
+
+  std::vector<float> usernormal = attrib.normals;
+  std::vector<float> usertexcoord = attrib.texcoords;
+  std::vector<int> userface;
+  std::vector<int> userfacenormal;
+  std::vector<int> userfacetexcoord;
+
+  if (!obj_reader.GetShapes().empty()) {
+    const auto& obj_mesh = obj_reader.GetShapes()[0].mesh;
+
+    std::vector<tinyobj::index_t> face_indices;
+    for (size_t face = 0, idx = 0; idx < obj_mesh.indices.size();) {
+      int nfacevert = obj_mesh.num_face_vertices[face];
+      if (nfacevert < 3 || nfacevert > 4) {
+        mju_warning(
+            "obj_decoder: only tri or quad meshes are supported (file '%s')",
+            resource->name);
+        mj_deleteSpec(spec);
+        return nullptr;
+      }
+
+      face_indices.push_back(obj_mesh.indices[idx]);
+      face_indices.push_back(obj_mesh.indices[idx + 1]);
+      face_indices.push_back(obj_mesh.indices[idx + 2]);
+
+      if (nfacevert == 4) {
+        face_indices.push_back(obj_mesh.indices[idx]);
+        face_indices.push_back(obj_mesh.indices[idx + 2]);
+        face_indices.push_back(obj_mesh.indices[idx + 3]);
+      }
+      idx += nfacevert;
+      ++face;
+    }
+
+    for (const auto& mesh_index : face_indices) {
+      userface.push_back(mesh_index.vertex_index);
+
+      if (!usernormal.empty()) {
+        userfacenormal.push_back(mesh_index.normal_index);
+      }
+
+      if (!usertexcoord.empty()) {
+        userfacetexcoord.push_back(mesh_index.texcoord_index);
+      }
+    }
+  }
+
+  for (size_t i = 0; i < usertexcoord.size() / 2; i++) {
+    usertexcoord[2 * i + 1] = 1 - usertexcoord[2 * i + 1];
+  }
+
+  mjs_setString(mesh->file, resource->name);
+  mjs_setFloat(mesh->uservert, attrib.vertices.data(), attrib.vertices.size());
+  mjs_setFloat(mesh->usernormal, usernormal.data(), usernormal.size());
+  mjs_setFloat(mesh->usertexcoord, usertexcoord.data(), usertexcoord.size());
+  mjs_setInt(mesh->userface, userface.data(), userface.size());
+  mjs_setInt(mesh->userfacenormal, userfacenormal.data(), userfacenormal.size());
+  mjs_setInt(mesh->userfacetexcoord, userfacetexcoord.data(), userfacetexcoord.size());
+
+  return spec;
+}
+
+int CanDecode(const mjResource* resource) {
+  std::string_view name(resource->name);
+  return name.ends_with(".obj") || name.ends_with(".OBJ");
+}
+
+}  // namespace
+
+mjPLUGIN_LIB_INIT {
+  mjpDecoder decoder;
+  mjp_defaultDecoder(&decoder);
+  decoder.content_type = "model/obj";
+  decoder.extension = ".obj";
+  decoder.decode = Decode;
+  decoder.can_decode = CanDecode;
+  mjp_registerDecoder(&decoder);
+}