Viewports: store ImGuiViewport* ParentViewport pointer as well. Backends: SDL3, Win32: use this pointer to reduce lookups. (#8948)

backends/imgui_impl_sdl3.cpp

@@ -1008,14 +1008,13 @@ struct ImGui_ImplSDL3_ViewportData
     ~ImGui_ImplSDL3_ViewportData()  { IM_ASSERT(Window == nullptr && GLContext == nullptr); }
 };
 
-static SDL_Window* ImGui_ImplSDL3_GetSDLWindowFromViewportID(ImGuiID viewport_id)
+static SDL_Window* ImGui_ImplSDL3_GetSDLWindowFromViewport(ImGuiViewport* viewport)
 {
-    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);
-        }
+    if (viewport != nullptr)
+    {
+        SDL_WindowID window_id = (SDL_WindowID)(intptr_t)viewport->PlatformHandle;
+        return SDL_GetWindowFromID(window_id);
+    }
     return nullptr;
 }
 
@@ -1025,7 +1024,7 @@ static void ImGui_ImplSDL3_CreateWindow(ImGuiViewport* viewport)
     ImGui_ImplSDL3_ViewportData* vd = IM_NEW(ImGui_ImplSDL3_ViewportData)();
     viewport->PlatformUserData = vd;
 
-    vd->ParentWindow = ImGui_ImplSDL3_GetSDLWindowFromViewportID(viewport->ParentViewportId);
+    vd->ParentWindow = ImGui_ImplSDL3_GetSDLWindowFromViewport(viewport->ParentViewport);
 
     ImGuiViewport* main_viewport = ImGui::GetMainViewport();
     ImGui_ImplSDL3_ViewportData* main_viewport_data = (ImGui_ImplSDL3_ViewportData*)main_viewport->PlatformUserData;
@@ -1114,7 +1113,7 @@ static void ImGui_ImplSDL3_UpdateWindow(ImGuiViewport* viewport)
 #ifndef __APPLE__ // On Mac, SDL3 Parenting appears to prevent viewport from appearing in another monitor
     // 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);
+    SDL_Window* new_parent = ImGui_ImplSDL3_GetSDLWindowFromViewport(viewport->ParentViewport);
     if (new_parent != vd->ParentWindow)
     {
         vd->ParentWindow = new_parent;

backends/imgui_impl_win32.cpp

@@ -1123,11 +1123,10 @@ static void ImGui_ImplWin32_GetWin32StyleFromViewportFlags(ImGuiViewportFlags fl
         *out_ex_style |= WS_EX_TOPMOST;
 }
 
-static HWND ImGui_ImplWin32_GetHwndFromViewportID(ImGuiID viewport_id)
+static HWND ImGui_ImplWin32_GetHwndFromViewport(ImGuiViewport* viewport)
 {
-    if (viewport_id != 0)
-        if (ImGuiViewport* viewport = ImGui::FindViewportByID(viewport_id))
-            return (HWND)viewport->PlatformHandle;
+    if (viewport != nullptr)
+        return (HWND)viewport->PlatformHandle;
     return nullptr;
 }
 
@@ -1138,7 +1137,7 @@ static void ImGui_ImplWin32_CreateWindow(ImGuiViewport* viewport)
 
     // Select style and parent window
     ImGui_ImplWin32_GetWin32StyleFromViewportFlags(viewport->Flags, &vd->DwStyle, &vd->DwExStyle);
-    vd->HwndParent = ImGui_ImplWin32_GetHwndFromViewportID(viewport->ParentViewportId);
+    vd->HwndParent = ImGui_ImplWin32_GetHwndFromViewport(viewport->ParentViewport);
 
     // Create window
     RECT rect = { (LONG)viewport->Pos.x, (LONG)viewport->Pos.y, (LONG)(viewport->Pos.x + viewport->Size.x), (LONG)(viewport->Pos.y + viewport->Size.y) };
@@ -1201,7 +1200,7 @@ static void ImGui_ImplWin32_UpdateWindow(ImGuiViewport* viewport)
 
     // Update Win32 parent if it changed _after_ creation
     // Unlike style settings derived from configuration flags, this is more likely to change for advanced apps that are manipulating ParentViewportID manually.
-    HWND new_parent = ImGui_ImplWin32_GetHwndFromViewportID(viewport->ParentViewportId);
+    HWND new_parent = ImGui_ImplWin32_GetHwndFromViewport(viewport->ParentViewport);
     if (new_parent != vd->HwndParent)
     {
         // Win32 windows can either have a "Parent" (for WS_CHILD window) or an "Owner" (which among other thing keeps window above its owner).

docs/CHANGELOG.txt

@@ -118,6 +118,7 @@ Docking+Viewports Branch:
   Note that for GLFW/SDL2/OSX backends, which do not support honoring ParentViewportID.
   setting io.ConfigViewportsNoDefaultParent=true will align imgui's expectation
   with what the backend does.
+- Viewports: storing `ImGuiViewport* ParentViewport` pointer along with ParentViewportID.
 - Viewports: DestroyContext() does not call DestroyPlatformWindows() anymore at
   it assumed to be unnecessary as backensd should have done it and we check that
   backends have been shutdown since 1.90.4. Changed into asserts. (#7175, #8945)

imgui.cpp

@@ -17023,11 +17023,22 @@ void ImGui::WindowSyncOwnedViewport(ImGuiWindow* window, ImGuiWindow* parent_win
     // Update parent viewport ID
     // (the !IsFallbackWindow test mimic the one done in WindowSelectViewport())
     if (window->WindowClass.ParentViewportId != (ImGuiID)-1)
+    {
+        ImGuiID old_parent_viewport_id = window->Viewport->ParentViewportId;
         window->Viewport->ParentViewportId = window->WindowClass.ParentViewportId;
+        if (window->Viewport->ParentViewportId != old_parent_viewport_id)
+            window->Viewport->ParentViewport = FindViewportByID(window->Viewport->ParentViewportId);
+    }
     else if ((window_flags & (ImGuiWindowFlags_Popup | ImGuiWindowFlags_Tooltip)) && parent_window_in_stack && (!parent_window_in_stack->IsFallbackWindow || parent_window_in_stack->WasActive))
+    {
+        window->Viewport->ParentViewport = parent_window_in_stack->Viewport;
         window->Viewport->ParentViewportId = parent_window_in_stack->Viewport->ID;
+    }
     else
+    {
+        window->Viewport->ParentViewport = g.IO.ConfigViewportsNoDefaultParent ? NULL : GetMainViewport();
         window->Viewport->ParentViewportId = g.IO.ConfigViewportsNoDefaultParent ? 0 : IMGUI_VIEWPORT_DEFAULT_ID;
+    }
 }
 
 // Called by user at the end of the main loop, after EndFrame()

imgui.h

@@ -29,7 +29,7 @@
 // Library Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals, e.g. '#if IMGUI_VERSION_NUM >= 12345')
 #define IMGUI_VERSION       "1.92.4 WIP"
-#define IMGUI_VERSION_NUM   19233
+#define IMGUI_VERSION_NUM   19234
 #define IMGUI_HAS_TABLE             // Added BeginTable() - from IMGUI_VERSION_NUM >= 18000
 #define IMGUI_HAS_TEXTURES          // Added ImGuiBackendFlags_RendererHasTextures - from IMGUI_VERSION_NUM >= 19198
 #define IMGUI_HAS_VIEWPORT          // In 'docking' WIP branch.
@@ -4044,6 +4044,7 @@ struct ImGuiViewport
     ImVec2              WorkSize;               // Work Area: Size of the viewport minus task bars, menu bars, status bars (<= Size)
     float               DpiScale;               // 1.0f = 96 DPI = No extra scale.
     ImGuiID             ParentViewportId;       // (Advanced) 0: no parent. Instruct the platform backend to setup a parent/child relationship between platform windows.
+    ImGuiViewport*      ParentViewport;         // (Advanced) == ImGui::FindViewportByID(ParentViewportId)
     ImDrawData*         DrawData;               // The ImDrawData corresponding to this viewport. Valid after Render() and until the next call to NewFrame().
 
     // Platform/Backend Dependent Data