Move STL handling to a mjpDecoder.

PiperOrigin-RevId: 880820344
Change-Id: Ib3a714dd9698335433e518ed6af17d7b8407a8fb

.github/workflows/build_steps.sh

@@ -102,6 +102,7 @@ copy_plugins_posix() {
     cp lib/libactuator.* ${TMPDIR}/mujoco_install/mujoco_plugin &&
     cp lib/libelasticity.* ${TMPDIR}/mujoco_install/mujoco_plugin &&
     cp lib/libobj_decoder.* ${TMPDIR}/mujoco_install/mujoco_plugin &&
+    cp lib/libstl_decoder.* ${TMPDIR}/mujoco_install/mujoco_plugin &&
     cp lib/libsensor.* ${TMPDIR}/mujoco_install/mujoco_plugin &&
     cp lib/libsdf_plugin.* ${TMPDIR}/mujoco_install/mujoco_plugin
 }
@@ -113,6 +114,7 @@ copy_plugins_window() {
     cp bin/Release/actuator.dll ${TMPDIR}/mujoco_install/mujoco_plugin &&
     cp bin/Release/elasticity.dll ${TMPDIR}/mujoco_install/mujoco_plugin &&
     cp bin/Release/obj_decoder.dll ${TMPDIR}/mujoco_install/mujoco_plugin &&
+    cp bin/Release/stl_decoder.dll ${TMPDIR}/mujoco_install/mujoco_plugin &&
     cp bin/Release/sensor.dll ${TMPDIR}/mujoco_install/mujoco_plugin
 }
 

CMakeLists.txt

@@ -111,6 +111,7 @@ if(NOT EMSCRIPTEN)
   add_subdirectory(plugin/sdf)
 endif()
 add_subdirectory(plugin/obj_decoder)
+add_subdirectory(plugin/stl_decoder)
 add_subdirectory(src/engine)
 add_subdirectory(src/user)
 add_subdirectory(src/xml)

plugin/stl_decoder/CMakeLists.txt

@@ -0,0 +1,54 @@
+# 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
+#
+#   https://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.
+
+if(EMSCRIPTEN)
+  add_library(stl_decoder OBJECT stl_decoder.cc)
+else()
+  set(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)
+  set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_LIBDIR}")
+
+  add_library(stl_decoder SHARED stl_decoder.cc)
+endif()
+
+target_include_directories(stl_decoder PRIVATE
+  ${CMAKE_CURRENT_SOURCE_DIR}/../..
+  ${CMAKE_CURRENT_SOURCE_DIR}/../../include
+)
+
+if(EMSCRIPTEN)
+  target_link_libraries(stl_decoder PRIVATE)
+else()
+  target_link_libraries(stl_decoder PRIVATE
+    mujoco
+  )
+endif()
+
+target_compile_options(stl_decoder PRIVATE
+  ${AVX_COMPILE_OPTIONS}
+  ${MUJOCO_MACOS_COMPILE_OPTIONS}
+  ${EXTRA_COMPILE_OPTIONS}
+  ${MUJOCO_CXX_FLAGS}
+)
+
+if(NOT EMSCRIPTEN)
+  target_link_options(stl_decoder PRIVATE
+    ${MUJOCO_MACOS_LINK_OPTIONS}
+    ${EXTRA_LINK_OPTIONS}
+  )
+
+  install(
+    TARGETS stl_decoder
+    LIBRARY DESTINATION "${CMAKE_INSTALL_BINDIR}/mujoco_plugin"
+  )
+endif()

plugin/stl_decoder/stl_decoder.cc

@@ -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);
+}

src/user/user_mesh.cc

@@ -614,10 +614,6 @@ void mjCMesh::ProcessVertices(const std::vector<float>& vert, bool remove_repeat
 
 
 
-bool mjCMesh::IsSTL(std::string_view filename, std::string_view ct) {
-  std::string asset_type = GetAssetContentType(filename, ct);
-  return asset_type == "model/stl";
-}
 
 bool mjCMesh::IsMSH(std::string_view filename, std::string_view ct) {
   std::string asset_type = GetAssetContentType(filename, ct);
@@ -626,9 +622,6 @@ bool mjCMesh::IsMSH(std::string_view filename, std::string_view ct) {
 
 
 
-bool mjCMesh::IsSTL() const {
-  return content_type_ == "model/stl";
-}
 
 bool mjCMesh::IsMSH() const {
   return content_type_ == "model/vnd.mujoco.msh";
@@ -684,9 +677,7 @@ void mjCMesh::LoadFromResource(mjResource* resource, bool remove_repeated) {
   std::string asset_type = GetAssetContentType(resource->name, content_type_);
   content_type_ = asset_type;
 
-  if (IsSTL()) {
+  if (IsMSH()) {
-    LoadSTL(resource);
-  } else if (IsMSH()) {
     LoadMSH(resource, remove_repeated);
   } else {
     LoadFromDecoder(resource, remove_repeated);
@@ -1115,77 +1106,6 @@ bool mjCMesh::LoadCachedMesh(mjCCache *cache, const mjResource* resource) {
 
 
 
-// load STL binary mesh
-void mjCMesh::LoadSTL(mjResource* resource) {
-  bool righthand = scale[0] * scale[1] * scale[2] > 0;
-
-  // get file data in buffer
-  char* buffer = 0;
-  int buffer_sz = mju_readResource(resource, (const void**)&buffer);
-
-  // still not found
-  if (buffer_sz < 0) {
-    throw mjCError(this, "could not read STL file '%s'", resource->name);
-  } else if (!buffer_sz) {
-    throw mjCError(this, "STL file '%s' is empty", resource->name);
-  }
-
-  // make sure there is enough data for header
-  if (buffer_sz < 84) {
-    throw mjCError(this, "invalid header in STL file '%s'", resource->name);
-  }
-
-  // get number of triangles, check bounds
-  int nfaces = 0;
-  ReadFromBuffer(&nfaces, buffer + 80);
-  if (nfaces < 1 || nfaces > 200000) {
-    throw mjCError(this,
-                   "number of faces should be between 1 and 200000 in STL file '%s';"
-                   " perhaps this is an ASCII file?", resource->name);
-  }
-
-  // check remaining buffer size
-  if (nfaces*50 != buffer_sz-84) {
-    throw mjCError(this,
-                   "STL file '%s' has wrong size; perhaps this is an ASCII file?",
-                   resource->name);
-  }
-
-  // assign stl data pointer
-  const char* stl = buffer + 84;
-
-  // allocate face and vertex data
-  face_.assign(3*nfaces, 0);
-  std::vector<float> vert;
-
-  // add vertices and faces, including repeated for now
-  for (int i=0; i < nfaces; i++) {
-    for (int j=0; j < 3; j++) {
-      // read vertex coordinates
-      float v[3];
-      ReadFromBuffer(&v, stl + 50*i + 12*(j + 1));
-
-      // check if vertex can be cast to an int safely
-      if (fabs(v[0]) > pow(2, 30) || fabs(v[1]) > pow(2, 30) || fabs(v[2]) > pow(2, 30)) {
-        throw mjCError(this, "vertex in STL file '%s' exceed maximum bounds", resource->name);
-      }
-
-      // add vertex address in face; change order if scale makes it lefthanded
-      if (righthand || j == 0) {
-        face_[3*i + j] = vert.size() / 3;
-      } else {
-        face_[3*i + 3 - j] = vert.size() / 3;
-      }
-
-      // add vertex data
-      vert.push_back(v[0]);
-      vert.push_back(v[1]);
-      vert.push_back(v[2]);
-    }
-  }
-  ProcessVertices(vert, true);
-}
-
 
 
 // load MSH binary mesh

wasm/CMakeLists.txt

@@ -60,6 +60,6 @@ set_target_properties(mujoco_wasm PROPERTIES
     OUTPUT_NAME "mujoco"
 )
 
-target_link_libraries(mujoco_wasm ccd lodepng mujoco tinyxml2 qhullstatic_r obj_decoder)
+target_link_libraries(mujoco_wasm ccd lodepng mujoco tinyxml2 qhullstatic_r obj_decoder stl_decoder)
 
 install(TARGETS mujoco_wasm DESTINATION ${DIVISIBLE_INSTALL_BIN_DIR})

wasm/tests/CMakeLists.txt

@@ -53,6 +53,6 @@ add_executable(mujoco_wasm_benchmark ${MUJOCO_WASM_FILES})
 
 set_target_properties(mujoco_wasm_benchmark PROPERTIES LINK_FLAGS "${EMCC_LINKER_FLAGS_STR}")
 
-target_link_libraries(mujoco_wasm_benchmark ccd lodepng mujoco tinyxml2 qhullstatic_r obj_decoder)
+target_link_libraries(mujoco_wasm_benchmark ccd lodepng mujoco tinyxml2 qhullstatic_r obj_decoder stl_decoder)
 
 install(TARGETS mujoco_wasm_benchmark DESTINATION ${DIVISIBLE_INSTALL_BIN_DIR})