Update logic for dealing with file dialogs.

This in preparation for an upcoming change that uses native file dialogs instead
of our very basic ImGui file dialog.

PiperOrigin-RevId: 861671041
Change-Id: I9b00c05efdda5e37ffe15048a2ccf66f6eca89d9

src/experimental/platform/CMakeLists.txt

@@ -37,6 +37,8 @@ target_compile_definitions(${MUJOCO_PLATFORM_TARGET_NAME}
 
 target_sources(${MUJOCO_PLATFORM_TARGET_NAME}
     PUBLIC
+        file_dialog.cc
+        file_dialog.h
         gui.cc
         gui.h
         helpers.cc

src/experimental/platform/file_dialog.cc

@@ -0,0 +1,67 @@
+// 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 "experimental/platform/file_dialog.h"
+
+#include <cstring>
+
+#include <span>
+#include <string>
+#include <string_view>
+
+#include <imgui.h>
+
+namespace mujoco::platform {
+
+static DialogResult ImGui_FileDialog(std::string_view path) {
+  static constexpr int kBufferSize = 1024;
+  char buf[kBufferSize];
+  std::strncpy(buf, path.data(), sizeof(buf));
+  buf[sizeof(buf) - 1] = '\0';
+
+  DialogResult::Status status = DialogResult::kPending;
+
+  ImGui::Text("Filename");
+  ImGui::SameLine();
+  ImGui::SetNextItemWidth(600);
+  if (ImGui::InputText("##Filename", buf, kBufferSize, ImGuiInputTextFlags_EnterReturnsTrue)) {
+    status = DialogResult::kAccepted;
+  }
+  if (ImGui::Button("OK", ImVec2(120, 0)) || ImGui::IsKeyChordPressed(ImGuiKey_Enter)) {
+    status = DialogResult::kAccepted;
+  }
+  ImGui::SetItemDefaultFocus();
+  ImGui::SameLine();
+  if (ImGui::Button("Cancel", ImVec2(120, 0)) || ImGui::IsKeyChordPressed(ImGuiKey_Escape)) {
+    status = DialogResult::kCancelled;
+  }
+
+  return DialogResult{.status = status, .path = std::string(buf)};
+}
+
+DialogResult OpenFileDialog(std::string_view path,
+                            std::span<std::string_view> filters) {
+  return ImGui_FileDialog(path);
+}
+
+DialogResult SaveFileDialog(std::string_view path,
+                            std::span<std::string_view> filters) {
+  return ImGui_FileDialog(path);
+}
+
+DialogResult SelectPathDialog(std::string_view path) {
+  return ImGui_FileDialog(path);
+}
+
+}  // namespace mujoco::platform

src/experimental/platform/file_dialog.h

@@ -0,0 +1,59 @@
+// 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.
+
+#ifndef MUJOCO_SRC_EXPERIMENTAL_PLATFORM_FILE_DIALOG_H_
+#define MUJOCO_SRC_EXPERIMENTAL_PLATFORM_FILE_DIALOG_H_
+
+#include <span>
+#include <string>
+#include <string_view>
+
+namespace mujoco::platform {
+
+// Result returned by various file dialog functions.
+struct DialogResult {
+  // The status of the dialog.
+  enum Status {
+    // The dialog is still open.
+    kPending,
+    // A file/folder was selected.
+    kAccepted,
+    // The dialog was dismissed.
+    kCancelled,
+    // An error occurred.
+    kError,
+  };
+
+  // The status of the dialog.
+  Status status = kPending;
+
+  // The path selected by the dialog if Status is kAccepted. If status is
+  // kError, the path may contain an error message. Empty otherwise.
+  std::string path;
+};
+
+// Opens a file dialog used for selecting a file to open.
+DialogResult OpenFileDialog(std::string_view path,
+                            std::span<std::string_view> filters = {});
+
+// Opens a file dialog used for selecting a file to save.
+DialogResult SaveFileDialog(std::string_view path,
+                            std::span<std::string_view> filters = {});
+
+// Opens a file dialog used for selecting a folder.
+DialogResult SelectPathDialog(std::string_view path);
+
+}  // namespace mujoco::platform
+
+#endif  // MUJOCO_SRC_EXPERIMENTAL_PLATFORM_FILE_DIALOG_H_

src/experimental/platform/imgui_widgets.cc

@@ -66,27 +66,6 @@ bool ImGui_Slider(const char* name, mjtNum* value, mjtNum min, mjtNum max) {
   return res;
 }
 
-bool ImGui_FileDialog(char* buf, int len) {
-  bool ok = false;
-  ImGui::Text("Filename");
-  ImGui::SameLine();
-  ImGui::SetNextItemWidth(600);
-  if (ImGui::InputText("##Filename", buf, len, ImGuiInputTextFlags_EnterReturnsTrue)) {
-    ok = true;
-    ImGui::CloseCurrentPopup();
-  };
-  if (ImGui::Button("OK", ImVec2(120, 0)) || ImGui_IsChordJustPressed(ImGuiKey_Enter)) {
-    ok = true;
-    ImGui::CloseCurrentPopup();
-  }
-  ImGui::SetItemDefaultFocus();
-  ImGui::SameLine();
-  if (ImGui::Button("Cancel", ImVec2(120, 0)) || ImGui_IsChordJustPressed(ImGuiKey_Escape)) {
-    ImGui::CloseCurrentPopup();
-  }
-  return ok;
-}
-
 void MaybeSaveToClipboard(const std::string& contents) {
   if (ImGui::GetIO().SetClipboardTextFn) {
     ImGui::GetIO().SetClipboardTextFn(nullptr, contents.c_str());

src/experimental/platform/imgui_widgets.h

@@ -131,9 +131,6 @@ struct ScopedStyle {
   int num_vars = 0;
 };
 
-// ImGui file dialog.
-bool ImGui_FileDialog(char* buf, int len);
-
 // ImGui Slider that supports both float and double types.
 bool ImGui_Slider(const char* name, mjtNum* value, mjtNum min, mjtNum max);
 

src/experimental/platform/window.cc

@@ -164,6 +164,13 @@ void Window::SetTitle(std::string_view title) {
   SDL_SetWindowTitle(sdl_window_, title.data());
 }
 
+void Window::DisableWindowResizing() {
+  SDL_SetWindowResizable(sdl_window_, SDL_FALSE);
+}
+void Window::EnableWindowResizing() {
+  SDL_SetWindowResizable(sdl_window_, SDL_TRUE);
+}
+
 std::string Window::GetDropFile() {
   std::string tmp;
   std::swap(tmp, drop_file_);

src/experimental/platform/window.h

@@ -82,6 +82,12 @@ class Window {
   // the value will be cleared until the next time a file is dropped.
   std::string GetDropFile();
 
+  // Enables window resizing.
+  void EnableWindowResizing();
+
+  // Disables window resizing.
+  void DisableWindowResizing();
+
   // Returns the handle to the underlying native window.
   void* GetNativeWindowHandle() { return native_window_; }
 

src/experimental/studio/app.cc

@@ -33,6 +33,7 @@
 #include <implot.h>
 #include <mujoco/mujoco.h>
 #include "experimental/platform/gui.h"
+#include "experimental/platform/file_dialog.h"
 #include "experimental/platform/helpers.h"
 #include "experimental/platform/imgui_widgets.h"
 #include "experimental/platform/interaction.h"
@@ -64,12 +65,6 @@ static void ToggleWindow(bool& window) {
   ImGui::GetIO().WantSaveIniSettings = true;
 }
 
-static void ShowFileDialog(bool& dialog) {
-  #ifndef __EMSCRIPTEN__
-    dialog = true;
-  #endif
-}
-
 static void SelectParentPerturb(const mjModel* model, mjvPerturb& perturb) {
   if (perturb.select > 0) {
     perturb.select = model->body_parentid[perturb.select];
@@ -314,12 +309,18 @@ void App::UpdateFilePaths(const std::string& resolved_path) {
     const std::filesystem::path path(resolved_path);
     const std::string base_path = path.parent_path().string() + "/";
     const std::string model_name = path.stem().string();
-    tmp_.last_load_file = base_path + model_name + ".xml";
+    tmp_.last_path[UiTempState::FileDialog_Load] =
-    tmp_.last_save_mjb_file = base_path + model_name + "_saved.mjb";
+        base_path + model_name + ".xml";
-    tmp_.last_save_xml_file = base_path + model_name + "_saved.xml";
+    tmp_.last_path[UiTempState::FileDialog_SaveMjb] =
-    tmp_.last_print_model_file = base_path + model_name + "_MJMODEL.TXT";
+        base_path + model_name + "_saved.mjb";
-    tmp_.last_print_data_file = base_path + model_name + "_MJDATA.TXT";
+    tmp_.last_path[UiTempState::FileDialog_SaveXml] =
-    tmp_.last_save_screenshot_file = base_path + "screenshot.webp";
+        base_path + model_name + "_saved.xml";
+    tmp_.last_path[UiTempState::FileDialog_PrintModel] =
+        base_path + model_name + "_MJMODEL.TXT";
+    tmp_.last_path[UiTempState::FileDialog_PrintData] =
+        base_path + model_name + "_MJDATA.TXT";
+    tmp_.last_path[UiTempState::FileDialog_SaveScreenshot] =
+        base_path + "screenshot.webp";
   }
 }
 
@@ -415,7 +416,7 @@ bool App::Update() {
 
   // Only update the simulation if a popup window is not open. Note that the
   // simulation itself will only update if it is not paused.
-  if (!tmp_.modal_open) {
+  if (tmp_.file_dialog == UiTempState::FileDialog_None) {
     UpdatePhysics();
   }
 
@@ -603,17 +604,17 @@ void App::HandleKeyboardEvents() {
 
   // Menu shortcuts.
   if (ImGui_IsChordJustPressed(ImGuiKey_O | ImGuiMod_Ctrl)) {
-    ShowFileDialog(tmp_.load_popup);
+    tmp_.file_dialog = UiTempState::FileDialog_Load;
   } else if (ImGui_IsChordJustPressed(ImGuiKey_S | ImGuiMode_CtrlShift)) {
-    ShowFileDialog(tmp_.save_mjb_popup);
+    tmp_.file_dialog = UiTempState::FileDialog_SaveMjb;
   } else if (ImGui_IsChordJustPressed(ImGuiKey_S | ImGuiMod_Ctrl)) {
-    ShowFileDialog(tmp_.save_xml_popup);
+    tmp_.file_dialog = UiTempState::FileDialog_SaveXml;
   } else if (ImGui_IsChordJustPressed(ImGuiKey_M | ImGuiMod_Ctrl)) {
-    ShowFileDialog(tmp_.print_model_popup);
+    tmp_.file_dialog = UiTempState::FileDialog_PrintModel;
   } else if (ImGui_IsChordJustPressed(ImGuiKey_D | ImGuiMod_Ctrl)) {
-    ShowFileDialog(tmp_.print_data_popup);
+    tmp_.file_dialog = UiTempState::FileDialog_PrintData;
   } else if (ImGui_IsChordJustPressed(ImGuiKey_P | ImGuiMod_Ctrl)) {
-    ShowFileDialog(tmp_.save_screenshot_popup);
+    tmp_.file_dialog = UiTempState::FileDialog_SaveScreenshot;
   } else if (ImGui_IsChordJustPressed(ImGuiKey_C | ImGuiMod_Ctrl)) {
     std::string keyframe = platform::KeyframeToString(model_, data_, false);
     platform::MaybeSaveToClipboard(keyframe);
@@ -1596,24 +1597,24 @@ void App::MainMenuGui() {
     if (ImGui::BeginMenu("File")) {
       #ifndef __EMSCRIPTEN__
       if (ImGui::MenuItem("Open Model File", "Ctrl+O")) {
-        ShowFileDialog(tmp_.load_popup);
+        tmp_.file_dialog = UiTempState::FileDialog_Load;
       }
       ImGui::Separator();
       if (ImGui::MenuItem("Save XML", "Ctrl+S")) {
-        ShowFileDialog(tmp_.save_xml_popup);
+        tmp_.file_dialog = UiTempState::FileDialog_SaveXml;
       }
       if (ImGui::MenuItem("Save MJB", "Ctrl+Shift+S")) {
-        ShowFileDialog(tmp_.save_mjb_popup);
+        tmp_.file_dialog = UiTempState::FileDialog_SaveMjb;
       }
       if (ImGui::MenuItem("Save Screenshot", "Ctrl+P")) {
-        ShowFileDialog(tmp_.save_screenshot_popup);
+        tmp_.file_dialog = UiTempState::FileDialog_SaveScreenshot;
       }
       ImGui::Separator();
       if (ImGui::MenuItem("Print Model", "Ctrl+M")) {
-        ShowFileDialog(tmp_.print_model_popup);
+        tmp_.file_dialog = UiTempState::FileDialog_PrintModel;
       }
       if (ImGui::MenuItem("Print Data", "Ctrl+D")) {
-        ShowFileDialog(tmp_.print_data_popup);
+        tmp_.file_dialog = UiTempState::FileDialog_PrintData;
       }
       ImGui::Separator();
       #endif  // !__EMSCRIPTEN__
@@ -1728,110 +1729,66 @@ void App::MainMenuGui() {
 }
 
 void App::FileDialogGui() {
+  if (tmp_.file_dialog == UiTempState::FileDialog_None) {
+    return;
+  }
+
   ImVec2 center = ImGui::GetMainViewport()->GetCenter();
   ImGui::SetNextWindowPos(center, ImGuiCond_Appearing, ImVec2(0.5f, 0.5f));
+  if (ImGui::BeginPopupModal("FileDialog", NULL,
+                             ImGuiWindowFlags_AlwaysAutoResize)) {
+    const platform::DialogResult res = platform::OpenFileDialog(tmp_.filename);
 
-  if (tmp_.load_popup) {
+    if (res.status == platform::DialogResult::kAccepted) {
-    ImGui::OpenPopup("LoadModel");
+      tmp_.last_path[tmp_.file_dialog] = res.path;
-    tmp_.load_popup = false;
+      switch (tmp_.file_dialog) {
-    strncpy(tmp_.filename, tmp_.last_load_file.c_str(),
+        case UiTempState::FileDialog_Load:
-            tmp_.last_load_file.size());
+          RequestModelLoad(res.path);
-    tmp_.filename[tmp_.last_load_file.size()] = 0;
+          break;
-  }
+        case UiTempState::FileDialog_SaveXml:
-  if (tmp_.save_xml_popup) {
+          mj_saveLastXML(res.path.c_str(), model_, nullptr, 0);
-    ImGui::OpenPopup("SaveXML");
+          break;
-    tmp_.save_xml_popup = false;
+        case UiTempState::FileDialog_SaveMjb:
-    strncpy(tmp_.filename, tmp_.last_save_xml_file.c_str(),
+          mj_saveModel(model_, res.path.c_str(), nullptr, 0);
-            tmp_.last_save_xml_file.size());
+          break;
-    tmp_.filename[tmp_.last_save_xml_file.size()] = 0;
+        case UiTempState::FileDialog_SaveScreenshot: {
-  }
+          const int width = window_->GetWidth();
-  if (tmp_.save_mjb_popup) {
+          const int height = window_->GetHeight();
-    ImGui::OpenPopup("SaveMJB");
+          std::vector<std::byte> buffer(width * height * 3);
-    tmp_.save_mjb_popup = false;
+          renderer_->RenderToTexture(model_, data_, &camera_, width, height,
-    strncpy(tmp_.filename, tmp_.last_save_mjb_file.c_str(),
+                                     buffer.data());
-            tmp_.last_save_mjb_file.size());
+          platform::SaveToWebp(width, height, buffer.data(), res.path);
-    tmp_.filename[tmp_.last_save_mjb_file.size()] = 0;
+          break;
-  }
+        }
-  if (tmp_.save_screenshot_popup) {
+        case UiTempState::FileDialog_PrintModel:
-    ImGui::OpenPopup("SaveWebp");
+          mj_printModel(model_, res.path.c_str());
-    tmp_.save_screenshot_popup = false;
+          break;
-    strncpy(tmp_.filename, tmp_.last_save_screenshot_file.c_str(),
+        case UiTempState::FileDialog_PrintData:
-            tmp_.last_save_screenshot_file.size());
+          mj_printData(model_, data_, res.path.c_str());
-    tmp_.filename[tmp_.last_save_screenshot_file.size()] = 0;
+          break;
-  }
+        default:
-  if (tmp_.print_model_popup) {
+          break;
-    ImGui::OpenPopup("PrintModel");
+      }
-    tmp_.print_model_popup = false;
+    }
-    strncpy(tmp_.filename, tmp_.last_print_model_file.c_str(),
+
-            tmp_.last_print_model_file.size());
+    if (res.status != platform::DialogResult::kError) {
-    tmp_.filename[tmp_.last_print_model_file.size()] = 0;
+      strncpy(tmp_.filename, res.path.c_str(), res.path.size());
-  }
+      tmp_.filename[res.path.size()] = 0;
-  if (tmp_.print_data_popup) {
+    }
-    ImGui::OpenPopup("PrintData");
+    if (res.status != platform::DialogResult::kPending) {
-    tmp_.print_data_popup = false;
+      tmp_.file_dialog = UiTempState::FileDialog_None;
-    strncpy(tmp_.filename, tmp_.last_print_data_file.c_str(),
+      ImGui::CloseCurrentPopup();
-            tmp_.last_print_data_file.size());
+      window_->EnableWindowResizing();
-    tmp_.filename[tmp_.last_print_data_file.size()] = 0;
+    }
+    ImGui::EndPopup();
   }
 
-  tmp_.modal_open =
+  if (!ImGui::IsPopupOpen("FileDialog")) {
-      ImGui::IsPopupOpen("LoadModel") || ImGui::IsPopupOpen("SaveXML") ||
+    const std::string& src = tmp_.last_path[tmp_.file_dialog];
-      ImGui::IsPopupOpen("SaveMJB") || ImGui::IsPopupOpen("SaveWebp") ||
+    strncpy(tmp_.filename, src.c_str(), src.size());
-      ImGui::IsPopupOpen("PrintModel") || ImGui::IsPopupOpen("PrintData");
+    tmp_.filename[src.size()] = 0;
-
+    ImGui::OpenPopup("FileDialog");
-  if (ImGui::BeginPopupModal("LoadModel", NULL,
+    window_->DisableWindowResizing();
-                             ImGuiWindowFlags_AlwaysAutoResize)) {
-    if (platform::ImGui_FileDialog(tmp_.filename, sizeof(tmp_.filename))) {
-      RequestModelLoad(tmp_.filename);
-      tmp_.last_load_file = tmp_.filename;
-    }
-    ImGui::EndPopup();
-  }
-  if (ImGui::BeginPopupModal("SaveXML", NULL,
-                             ImGuiWindowFlags_AlwaysAutoResize)) {
-    if (platform::ImGui_FileDialog(tmp_.filename, sizeof(tmp_.filename))) {
-      char err[1000] = "";
-      mj_saveLastXML(tmp_.filename, model_, err, 1000);
-      tmp_.last_save_xml_file = tmp_.filename;
-    }
-    ImGui::EndPopup();
-  }
-  if (ImGui::BeginPopupModal("SaveMJB", NULL,
-                             ImGuiWindowFlags_AlwaysAutoResize)) {
-    if (platform::ImGui_FileDialog(tmp_.filename, sizeof(tmp_.filename))) {
-      mj_saveModel(model_, tmp_.filename, nullptr, 0);
-      tmp_.last_save_mjb_file = tmp_.filename;
-    }
-    ImGui::EndPopup();
-  }
-  if (ImGui::BeginPopupModal("SaveWebp", NULL,
-                             ImGuiWindowFlags_AlwaysAutoResize)) {
-    if (platform::ImGui_FileDialog(tmp_.filename, sizeof(tmp_.filename))) {
-      const int width = window_->GetWidth();
-      const int height = window_->GetHeight();
-      std::vector<std::byte> buffer(width * height * 3);
-      renderer_->RenderToTexture(model_, data_, &camera_, width, height,
-                                 buffer.data());
-      platform::SaveToWebp(width, height, buffer.data(), tmp_.filename);
-      tmp_.last_save_screenshot_file = tmp_.filename;
-    }
-    ImGui::EndPopup();
-  }
-  if (ImGui::BeginPopupModal("PrintModel", NULL,
-                             ImGuiWindowFlags_AlwaysAutoResize)) {
-    if (platform::ImGui_FileDialog(tmp_.filename, sizeof(tmp_.filename))) {
-      mj_printModel(model_, tmp_.filename);
-      tmp_.last_print_model_file = tmp_.filename;
-    }
-    ImGui::EndPopup();
-  }
-  if (ImGui::BeginPopupModal("PrintData", NULL,
-                             ImGuiWindowFlags_AlwaysAutoResize)) {
-    if (platform::ImGui_FileDialog(tmp_.filename, sizeof(tmp_.filename))) {
-      mj_printData(model_, data_, tmp_.filename);
-      tmp_.last_print_data_file = tmp_.filename;
-    }
-    ImGui::EndPopup();
   }
 }
 

src/experimental/studio/app.h

@@ -104,8 +104,6 @@ class App {
     bool style_editor = false;
     bool imgui_demo = false;
     bool implot_demo = false;
-    bool modal_open = false;
-    bool load_popup = false;
 
     // Controls.
     bool perturb_active = false;
@@ -129,18 +127,19 @@ class App {
     std::vector<platform::PipState> pips;
 
     // File dialogs.
+    enum FileDialog {
+      FileDialog_None,
+      FileDialog_Load,
+      FileDialog_SaveXml,
+      FileDialog_SaveMjb,
+      FileDialog_PrintModel,
+      FileDialog_PrintData,
+      FileDialog_SaveScreenshot,
+      NumFileDialogs,
+    };
+    FileDialog file_dialog = FileDialog_None;
+    std::string last_path[NumFileDialogs];
     char filename[1000] = "";
-    std::string last_load_file;
-    bool save_xml_popup = false;
-    std::string last_save_xml_file;
-    bool save_mjb_popup = false;
-    std::string last_save_mjb_file;
-    bool save_screenshot_popup = false;
-    std::string last_save_screenshot_file;
-    bool print_model_popup = false;
-    std::string last_print_model_file;
-    bool print_data_popup = false;
-    std::string last_print_data_file;
   };
 
   // Requests that the model be loaded from the given file at the next update.