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_; }