Add 'Always on Top' and 'Reset Windows' features

 'Always on Top' window flag and a 'Reset Windows' action. Persisted window_always_on_top is applied to the main GLFW window and any detached GLFW-backed ImGui viewports via apply_glfw_topmost_state_to_platform_windows. Native file dialogs temporarily suspend the topmost hint using a FileDialog native-dialog-scope hook and RAII guard to avoid dialogs being obscured. Add Window menu entries for Always on Top and Reset Windows, and wire reset to clear ImGui .ini settings and rebuild the dockspace (reset_window_layouts). Overhaul Preferences UI (sectioned form layout, helpers, OCIO browse integration, segmented backend selector), convert About modal to a centered window, improve focus/request handling for auxiliary windows, and various UI/layout tweaks and plumbing to set/clear the native dialog hook in the app run loop.

Some UI refactoring

Signed-off-by: Vlad (Kuzmin) Erium <libalias@gmail.com>

Author: ssh4net

src/doc/imiv_dev.rst

@@ -461,7 +461,7 @@ The main windows are:
 * `iv Info`;
 * `iv Preferences`;
 * `Preview`;
-* the `About imiv` modal;
+* the `About imiv` window;
 * optional Dear ImGui diagnostics from the runtime-enabled `Developer` menu.
 
 Auxiliary windows in `src/imiv/imiv_aux_windows.cpp` use
@@ -503,6 +503,16 @@ Execution layer
 keeps file I/O, texture uploads, fullscreen changes, and navigation changes
 out of the immediate menu-building code.
 
+The same layer now also handles two window-management actions:
+
+* `Always on Top`
+  persists a simple boolean flag in `imiv.inf` and applies it to the main
+  GLFW window and any detached GLFW-backed ImGui viewport windows with
+  `GLFW_FLOATING`;
+* `Reset Windows`
+  clears live Dear ImGui ini settings, rebuilds the main dockspace, and
+  reapplies the standard auxiliary-window defaults for the current frame.
+
 Behavior layer
 --------------
 
@@ -527,6 +537,27 @@ When adding a feature, the normal path is:
 3. put the durable behavior in `imiv_actions.cpp` or shared helpers.
 
 
+Native dialog wrapper
+=====================
+
+`src/imiv/imiv_file_dialog.cpp` owns all native open/save/folder dialog calls.
+
+It also owns the temporary topmost suppression used by the `Always on Top`
+feature:
+
+* the app installs a lightweight begin/end callback once it has a live GLFW
+  window;
+* the file-dialog wrapper enters that scope before opening an NFD dialog and
+  leaves it afterward;
+* while the scope is active, the main GLFW window and any detached GLFW-backed
+  ImGui viewport windows have `GLFW_FLOATING` temporarily cleared;
+* after the dialog returns, the wrapper restores the persistent
+  `window_always_on_top` state.
+
+Keeping that logic in the dialog wrapper avoids threading platform window
+details through every individual open/save action.
+
+
 Image window and helper modules
 ===============================
 

src/doc/imiv_user.rst

@@ -311,6 +311,22 @@ multi-open and `Open Folder...`. That means dropped files immediately appear
 in `Image List` and participate in the same per-view open/close/remove
 workflow.
 
+The `Window` menu provides:
+
+* `Always on Top`
+  keeps the main :program:`imiv` window and detached auxiliary windows above
+  ordinary desktop windows;
+* `Reset Windows`
+  clears the saved Dear ImGui layout in the current session and restores the
+  default dock/tool-window placement so hidden or off-screen auxiliary windows
+  can be recovered.
+
+When native open/save/folder dialogs are used, :program:`imiv` temporarily
+disables the topmost window hint while the dialog is open and restores it
+after the dialog closes. This avoids the main window covering the native file
+dialog on platforms where an always-on-top GLFW window would otherwise stay in
+front.
+
 
 Color management
 ================
@@ -354,6 +370,7 @@ Saved state currently includes:
 * Dear ImGui docking/window layout;
 * viewer and preview defaults for the primary view;
 * backend preference (`renderer_backend`);
+* whether the main window is `Always on Top`;
 * OCIO settings;
 * recent images and sort mode.
 
@@ -362,6 +379,7 @@ Example::
     [ImivApp][State]
     renderer_backend=vulkan
     fit_image_to_window=1
+    window_always_on_top=0
     use_ocio=1
     ocio_display=default
     ocio_view=default

src/imiv/imiv_app.cpp

@@ -58,6 +58,13 @@ namespace Imiv {
 
 namespace {
 
+    struct NativeDialogWindowScope {
+        GLFWwindow* window            = nullptr;
+        PlaceholderUiState* ui_state  = nullptr;
+        int suspend_depth             = 0;
+        bool restore_floating_on_exit = false;
+    };
+
     std::filesystem::path executable_directory_path()
     {
         const std::string program_path = Sysutil::this_program_path();
@@ -254,6 +261,59 @@ namespace {
                                     backend_cli_name(active_backend));
     }
 
+    void apply_glfw_topmost_state_to_platform_windows(GLFWwindow* main_window,
+                                                      bool always_on_top)
+    {
+        if (main_window != nullptr)
+            platform_glfw_set_window_floating(main_window, always_on_top);
+
+        ImGuiContext* ctx = ImGui::GetCurrentContext();
+        if (ctx == nullptr)
+            return;
+        if ((ImGui::GetIO().ConfigFlags & ImGuiConfigFlags_ViewportsEnable)
+            == 0) {
+            return;
+        }
+
+        ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
+        for (int i = 0; i < platform_io.Viewports.Size; ++i) {
+            ImGuiViewport* viewport = platform_io.Viewports[i];
+            if (viewport == nullptr || viewport->PlatformHandle == nullptr)
+                continue;
+            GLFWwindow* viewport_window = static_cast<GLFWwindow*>(
+                viewport->PlatformHandle);
+            platform_glfw_set_window_floating(viewport_window, always_on_top);
+        }
+    }
+
+    void native_dialog_scope_callback(bool begin_scope, void* user_data)
+    {
+        auto* scope = static_cast<NativeDialogWindowScope*>(user_data);
+        if (scope == nullptr || scope->window == nullptr
+            || scope->ui_state == nullptr)
+            return;
+
+        if (begin_scope) {
+            ++scope->suspend_depth;
+            if (scope->suspend_depth == 1
+                && scope->ui_state->window_always_on_top
+                && platform_glfw_is_window_floating(scope->window)) {
+                apply_glfw_topmost_state_to_platform_windows(scope->window,
+                                                             false);
+                scope->restore_floating_on_exit = true;
+            }
+            return;
+        }
+
+        if (scope->suspend_depth > 0)
+            --scope->suspend_depth;
+        if (scope->suspend_depth == 0 && scope->restore_floating_on_exit) {
+            apply_glfw_topmost_state_to_platform_windows(
+                scope->window, scope->ui_state->window_always_on_top);
+            scope->restore_floating_on_exit = false;
+        }
+    }
+
     std::vector<std::string> expand_startup_input_paths(const AppConfig& config,
                                                         bool verbose_logging,
                                                         ImageSortMode sort_mode,
@@ -670,6 +730,12 @@ run(const AppConfig& config)
     }
     set_area_sample_enabled(viewer, ui_state, ui_state.show_area_probe_window);
     apply_imgui_app_style(sanitize_app_style_preset(ui_state.style_preset));
+    apply_glfw_topmost_state_to_platform_windows(window,
+                                                 ui_state.window_always_on_top);
+
+    NativeDialogWindowScope native_dialog_scope = { window, &ui_state };
+    FileDialog::set_native_dialog_scope_hook(native_dialog_scope_callback,
+                                             &native_dialog_scope);
 
     if (!run_config.input_paths.empty()) {
         append_loaded_image_paths(library, run_config.input_paths);
@@ -725,6 +791,10 @@ run(const AppConfig& config)
             center_glfw_window(window);
             --startup_center_frames;
         }
+        if (native_dialog_scope.suspend_depth == 0) {
+            apply_glfw_topmost_state_to_platform_windows(
+                window, ui_state.window_always_on_top);
+        }
 
         int fb_width  = 0;
         int fb_height = 0;
@@ -772,6 +842,10 @@ run(const AppConfig& config)
         if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable) {
             renderer_prepare_platform_windows(renderer_state);
             ImGui::UpdatePlatformWindows();
+            if (native_dialog_scope.suspend_depth == 0) {
+                apply_glfw_topmost_state_to_platform_windows(
+                    window, ui_state.window_always_on_top);
+            }
             ImGui::RenderPlatformWindowsDefault();
             renderer_finish_platform_windows(renderer_state);
         }
@@ -825,6 +899,7 @@ run(const AppConfig& config)
 #if defined(IMGUI_ENABLE_TEST_ENGINE)
     test_engine_stop(test_engine_runtime);
 #endif
+    FileDialog::set_native_dialog_scope_hook(nullptr, nullptr);
     uninstall_drag_drop(window);
     if (active_backend == BackendKind::OpenGL) {
         renderer_cleanup_window(renderer_state);