Backends: SDL3: added support for viewport->ParentViewportId field to support parenting windows at OS level. (#7973)

backends/imgui_impl_sdl3.cpp

@@ -13,7 +13,6 @@
 //  [x] Platform: Multi-viewport support (multiple windows). Enable with 'io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable' -> the OS animation effect when window gets created/destroyed is problematic. SDL2 backend doesn't have issue.
 // Issues:
 //  [ ] Platform: Multi-viewport: Minimized windows seems to break mouse wheel events (at least under Windows).
-//  [ ] Platform: Multi-viewport: ParentViewportID not honored, and so io.ConfigViewportsNoDefaultParent has no effect (minor).
 
 // You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
 // Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
@@ -26,6 +25,7 @@
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
 //  2024-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
+//  2024-09-11: (Docking) Added support for viewport->ParentViewportId field to support parenting at OS level. (#7973)
 //  2024-09-03: Update for SDL3 api changes: SDL_GetGamepads() memory ownership revert. (#7918, #7898, #7807)
 //  2024-08-22: moved some OS/backend related function pointers from ImGuiIO to ImGuiPlatformIO:
 //               - io.GetClipboardTextFn    -> platform_io.Platform_GetClipboardTextFn
@@ -905,20 +905,34 @@ void ImGui_ImplSDL3_NewFrame()
 struct ImGui_ImplSDL3_ViewportData
 {
     SDL_Window*     Window;
+    SDL_Window*     ParentWindow;
     Uint32          WindowID;
     bool            WindowOwned;
     SDL_GLContext   GLContext;
 
-    ImGui_ImplSDL3_ViewportData() { Window = nullptr; WindowID = 0; WindowOwned = false; GLContext = nullptr; }
+    ImGui_ImplSDL3_ViewportData() { Window = ParentWindow = nullptr; WindowID = 0; WindowOwned = false; GLContext = nullptr; }
     ~ImGui_ImplSDL3_ViewportData() { IM_ASSERT(Window == nullptr && GLContext == nullptr); }
 };
 
+static SDL_Window* ImGui_ImplSDL3_GetSDLWindowFromViewportID(ImGuiID viewport_id)
+{
+    if (viewport_id != 0)
+        if (ImGuiViewport* viewport = ImGui::FindViewportByID(viewport_id))
+        {
+            SDL_WindowID window_id = (SDL_WindowID)(intptr_t)viewport->PlatformHandle;
+            return SDL_GetWindowFromID(window_id);
+        }
+    return nullptr;
+}
+
 static void ImGui_ImplSDL3_CreateWindow(ImGuiViewport* viewport)
 {
     ImGui_ImplSDL3_Data* bd = ImGui_ImplSDL3_GetBackendData();
     ImGui_ImplSDL3_ViewportData* vd = IM_NEW(ImGui_ImplSDL3_ViewportData)();
     viewport->PlatformUserData = vd;
 
+    vd->ParentWindow = ImGui_ImplSDL3_GetSDLWindowFromViewportID(viewport->ParentViewportId);
+
     ImGuiViewport* main_viewport = ImGui::GetMainViewport();
     ImGui_ImplSDL3_ViewportData* main_viewport_data = (ImGui_ImplSDL3_ViewportData*)main_viewport->PlatformUserData;
 
@@ -943,6 +957,7 @@ static void ImGui_ImplSDL3_CreateWindow(ImGuiViewport* viewport)
 #endif
     sdl_flags |= (viewport->Flags & ImGuiViewportFlags_TopMost) ? SDL_WINDOW_ALWAYS_ON_TOP : 0;
     vd->Window = SDL_CreateWindow("No Title Yet", (int)viewport->Size.x, (int)viewport->Size.y, sdl_flags);
+    SDL_SetWindowParent(vd->Window, vd->ParentWindow);
     SDL_SetWindowPosition(vd->Window, (int)viewport->Pos.x, (int)viewport->Pos.y);
     vd->WindowOwned = true;
     if (use_opengl)
@@ -992,6 +1007,20 @@ static void ImGui_ImplSDL3_ShowWindow(ImGuiViewport* viewport)
     SDL_ShowWindow(vd->Window);
 }
 
+static void ImGui_ImplSDL3_UpdateWindow(ImGuiViewport* viewport)
+{
+    ImGui_ImplSDL3_ViewportData* vd = (ImGui_ImplSDL3_ViewportData*)viewport->PlatformUserData;
+
+    // Update SDL3 parent if it changed _after_ creation.
+    // This is for advanced apps that are manipulating ParentViewportID manually.
+    SDL_Window* new_parent = ImGui_ImplSDL3_GetSDLWindowFromViewportID(viewport->ParentViewportId);
+    if (new_parent != vd->ParentWindow)
+    {
+        vd->ParentWindow = new_parent;
+        SDL_SetWindowParent(vd->Window, vd->ParentWindow);
+    }
+}
+
 static ImVec2 ImGui_ImplSDL3_GetWindowPos(ImGuiViewport* viewport)
 {
     ImGui_ImplSDL3_ViewportData* vd = (ImGui_ImplSDL3_ViewportData*)viewport->PlatformUserData;
@@ -1085,6 +1114,7 @@ static void ImGui_ImplSDL3_InitPlatformInterface(SDL_Window* window, void* sdl_g
     platform_io.Platform_CreateWindow = ImGui_ImplSDL3_CreateWindow;
     platform_io.Platform_DestroyWindow = ImGui_ImplSDL3_DestroyWindow;
     platform_io.Platform_ShowWindow = ImGui_ImplSDL3_ShowWindow;
+    platform_io.Platform_UpdateWindow = ImGui_ImplSDL3_UpdateWindow;
     platform_io.Platform_SetWindowPos = ImGui_ImplSDL3_SetWindowPos;
     platform_io.Platform_GetWindowPos = ImGui_ImplSDL3_GetWindowPos;
     platform_io.Platform_SetWindowSize = ImGui_ImplSDL3_SetWindowSize;

backends/imgui_impl_sdl3.h

@@ -13,7 +13,6 @@
 //  [x] Platform: Multi-viewport support (multiple windows). Enable with 'io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable' -> the OS animation effect when window gets created/destroyed is problematic. SDL2 backend doesn't have issue.
 // Issues:
 //  [ ] Platform: Multi-viewport: Minimized windows seems to break mouse wheel events (at least under Windows).
-//  [ ] Platform: Multi-viewport: ParentViewportID not honored, and so io.ConfigViewportsNoDefaultParent has no effect (minor).
 //  [x] Platform: Basic IME support. Position somehow broken in SDL3 + app needs to call 'SDL_SetHint(SDL_HINT_IME_SHOW_UI, "1");' before SDL_CreateWindow()!.
 
 // You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.

docs/CHANGELOG.txt

@@ -67,6 +67,11 @@ Other changes:
 - TextLinkOpenURL(): modified tooltip to display a verb "Open 'xxxx'". (#7885, #7660)
 - Backends: SDL2: use SDL_Vulkan_GetDrawableSize() when available. (#7967, #3190) [@scribam]
 
+Docking+Viewports Branch:
+
+- Backends: SDL3: added support for viewport->ParentViewportId field to support parenting
+  windows at OS level. (#7973) [@RT2code]
+
 -----------------------------------------------------------------------
  VERSION 1.91.1 (Released 2024-09-04)
 -----------------------------------------------------------------------