Move STL handling to a mjpDecoder.

PiperOrigin-RevId: 880820344 Change-Id: Ib3a714dd9698335433e518ed6af17d7b8407a8fb
2026-03-09 06:14:23 -07:00
parent 330c36c99b
commit ed0d7ba29f
7 changed files with 203 additions and 83 deletions
@@ -0,0 +1,143 @@
+// 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 <cmath>
+#include <cstring>
+#include <map>
+#include <string_view>
+#include <vector>
+
+#include <mujoco/mjplugin.h>
+#include <mujoco/mjspec.h>
+#include <mujoco/mujoco.h>
+
+namespace {
+
+template <typename T>
+void ReadFromBuffer(T* dst, const char* src) {
+  std::memcpy(dst, src, sizeof(T));
+}
+
+struct Vec3Key {
+  int x, y, z;
+  bool operator<(const Vec3Key& o) const {
+    if (x != o.x) return x < o.x;
+    if (y != o.y) return y < o.y;
+    return z < o.z;
+  }
+};
+
+Vec3Key FloatToKey(const float v[3]) {
+  int x, y, z;
+  std::memcpy(&x, &v[0], sizeof(int));
+  std::memcpy(&y, &v[1], sizeof(int));
+  std::memcpy(&z, &v[2], sizeof(int));
+  return {x, y, z};
+}
+
+mjSpec* Decode(mjResource* resource, const mjVFS* vfs) {
+  const void* bytes = nullptr;
+  int buffer_sz = mju_readResource(resource, &bytes);
+  if (buffer_sz < 0) {
+    mju_warning("stl_decoder: could not read STL file '%s'", resource->name);
+    return nullptr;
+  }
+  if (!buffer_sz) {
+    mju_warning("stl_decoder: STL file '%s' is empty", resource->name);
+    return nullptr;
+  }
+
+  const char* buffer = static_cast<const char*>(bytes);
+
+  if (buffer_sz < 84) {
+    mju_warning("stl_decoder: invalid header in STL file '%s'", resource->name);
+    return nullptr;
+  }
+
+  int nfaces = 0;
+  ReadFromBuffer(&nfaces, buffer + 80);
+  if (nfaces < 1 || nfaces > 200000) {
+    mju_warning(
+        "stl_decoder: number of faces should be between 1 and 200000 in STL "
+        "file '%s'; perhaps this is an ASCII file?",
+        resource->name);
+    return nullptr;
+  }
+
+  if (nfaces * 50 != buffer_sz - 84) {
+    mju_warning(
+        "stl_decoder: STL file '%s' has wrong size; perhaps this is an ASCII "
+        "file?",
+        resource->name);
+    return nullptr;
+  }
+
+  const char* stl = buffer + 84;
+
+  std::vector<float> uservert;
+  std::vector<int> userface(3 * nfaces, 0);
+  std::map<Vec3Key, int> vertmap;
+
+  for (int i = 0; i < nfaces; i++) {
+    for (int j = 0; j < 3; j++) {
+      float v[3];
+      ReadFromBuffer(&v, stl + 50 * i + 12 * (j + 1));
+
+      if (std::fabs(v[0]) > std::pow(2, 30) ||
+          std::fabs(v[1]) > std::pow(2, 30) ||
+          std::fabs(v[2]) > std::pow(2, 30)) {
+        mju_warning(
+            "stl_decoder: vertex in STL file '%s' "
+            "exceeds maximum bounds",
+            resource->name);
+        return nullptr;
+      }
+
+      Vec3Key key = FloatToKey(v);
+      auto [it, inserted] = vertmap.emplace(key, uservert.size() / 3);
+      if (inserted) {
+        uservert.push_back(v[0]);
+        uservert.push_back(v[1]);
+        uservert.push_back(v[2]);
+      }
+      userface[3 * i + j] = it->second;
+    }
+  }
+
+  mjSpec* spec = mj_makeSpec();
+  mjsMesh* mesh = mjs_addMesh(spec, nullptr);
+
+  mjs_setString(mesh->file, resource->name);
+  mjs_setFloat(mesh->uservert, uservert.data(), uservert.size());
+  mjs_setInt(mesh->userface, userface.data(), userface.size());
+
+  return spec;
+}
+
+int CanDecode(const mjResource* resource) {
+  std::string_view name(resource->name);
+  return name.ends_with(".stl") || name.ends_with(".STL");
+}
+
+}  // namespace
+
+mjPLUGIN_LIB_INIT {
+  mjpDecoder decoder;
+  mjp_defaultDecoder(&decoder);
+  decoder.content_type = "model/stl";
+  decoder.extension = ".stl";
+  decoder.decode = Decode;
+  decoder.can_decode = CanDecode;
+  mjp_registerDecoder(&decoder);
+}