Viewports: added ImGuiBackendFlags_HasParentViewportId backend flag. (#8948)

backends/imgui_impl_glfw.cpp

@@ -14,7 +14,7 @@
 // Missing features or Issues:
 //  [ ] Platform: Touch events are only correctly identified as Touch on Windows. This create issues with some interactions. GLFW doesn't provide a way to identify touch inputs from mouse inputs, we cannot call io.AddMouseSourceEvent() to identify the source. We provide a Windows-specific workaround.
 //  [ ] Platform: Missing ImGuiMouseCursor_Wait and ImGuiMouseCursor_Progress cursors.
-//  [ ] Platform: Multi-viewport: viewport->ParentViewportID is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
+//  [ ] Platform: Multi-viewport: Missing ImGuiBackendFlags_HasParentViewportId support. The viewport->ParentViewportID field is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
 
 // 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.

backends/imgui_impl_glfw.h

@@ -14,7 +14,7 @@
 // Missing features or Issues:
 //  [ ] Platform: Touch events are only correctly identified as Touch on Windows. This create issues with some interactions. GLFW doesn't provide a way to identify touch inputs from mouse inputs, we cannot call io.AddMouseSourceEvent() to identify the source. We provide a Windows-specific workaround.
 //  [ ] Platform: Missing ImGuiMouseCursor_Wait and ImGuiMouseCursor_Progress cursors.
-//  [ ] Platform: Multi-viewport: viewport->ParentViewportID is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
+//  [ ] Platform: Multi-viewport: Missing ImGuiBackendFlags_HasParentViewportId support. The viewport->ParentViewportID field is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
 
 // 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.

backends/imgui_impl_osx.h

@@ -13,7 +13,7 @@
 //  [x] Platform: Multi-viewport / platform windows.
 // Missing features or Issues:
 //  [ ] Platform: Multi-viewport: Window size not correctly reported when enabling io.ConfigViewportsNoDecoration
-//  [ ] Platform: Multi-viewport: viewport->ParentViewportID is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
+//  [ ] Platform: Multi-viewport: Missing ImGuiBackendFlags_HasParentViewportId support. The viewport->ParentViewportID field is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
 
 // 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.

backends/imgui_impl_osx.mm

@@ -13,7 +13,7 @@
 //  [x] Platform: Multi-viewport / platform windows.
 // Missing features or Issues:
 //  [ ] Platform: Multi-viewport: Window size not correctly reported when enabling io.ConfigViewportsNoDecoration
-//  [ ] Platform: Multi-viewport: viewport->ParentViewportID is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
+//  [ ] Platform: Multi-viewport: Missing ImGuiBackendFlags_HasParentViewportId support. The viewport->ParentViewportID field is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
 
 // 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.

backends/imgui_impl_sdl2.cpp

@@ -13,7 +13,7 @@
 //  [X] Platform: Multi-viewport support (multiple windows). Enable with 'io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable'.
 // Missing features or Issues:
 //  [ ] Platform: Multi-viewport: Minimized windows seems to break mouse wheel events (at least under Windows).
-//  [ ] Platform: Multi-viewport: viewport->ParentViewportID is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
+//  [ ] Platform: Multi-viewport: Missing ImGuiBackendFlags_HasParentViewportId support. The viewport->ParentViewportID field is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
 
 // 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.

backends/imgui_impl_sdl2.h

@@ -12,7 +12,7 @@
 //  [X] Platform: Multi-viewport support (multiple windows). Enable with 'io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable'.
 // Missing features or Issues:
 //  [ ] Platform: Multi-viewport: Minimized windows seems to break mouse wheel events (at least under Windows).
-//  [ ] Platform: Multi-viewport: viewport->ParentViewportID is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
+//  [ ] Platform: Multi-viewport: Missing ImGuiBackendFlags_HasParentViewportId support. The viewport->ParentViewportID field is ignored, and therefore io.ConfigViewportsNoDefaultParent has no effect either.
 
 // 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.

backends/imgui_impl_sdl3.cpp

@@ -534,7 +534,8 @@ static bool ImGui_ImplSDL3_Init(SDL_Window* window, SDL_Renderer* renderer, void
     io.BackendPlatformName = bd->BackendPlatformName;
     io.BackendFlags |= ImGuiBackendFlags_HasMouseCursors;           // We can honor GetMouseCursor() values (optional)
     io.BackendFlags |= ImGuiBackendFlags_HasSetMousePos;            // We can honor io.WantSetMousePos requests (optional, rarely used)
-    // (ImGuiBackendFlags_PlatformHasViewports may be set just below)
+    // (ImGuiBackendFlags_PlatformHasViewports and ImGuiBackendFlags_HasParentViewportId may be set just below)
+    // (ImGuiBackendFlags_HasMouseHoveredViewport is set dynamically in our _NewFrame function)
 
     bd->Window = window;
     bd->WindowID = SDL_GetWindowID(window);
@@ -560,7 +561,10 @@ static bool ImGui_ImplSDL3_Init(SDL_Window* window, SDL_Renderer* renderer, void
             bd->MouseCanUseGlobalState = bd->MouseCanUseCapture = true;
 #endif
     if (bd->MouseCanUseGlobalState)
+    {
         io.BackendFlags |= ImGuiBackendFlags_PlatformHasViewports;  // We can create multi-viewports on the Platform side (optional)
+        io.BackendFlags |= ImGuiBackendFlags_HasParentViewportId;   // We can honor viewport->ParentViewportId by applying the corresponding parent/child relationship at platform levle (optional)
+    }
 
     ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
     platform_io.Platform_SetClipboardTextFn = ImGui_ImplSDL3_SetClipboardText;
@@ -675,7 +679,7 @@ void ImGui_ImplSDL3_Shutdown()
 
     io.BackendPlatformName = nullptr;
     io.BackendPlatformUserData = nullptr;
-    io.BackendFlags &= ~(ImGuiBackendFlags_HasMouseCursors | ImGuiBackendFlags_HasSetMousePos | ImGuiBackendFlags_HasGamepad | ImGuiBackendFlags_PlatformHasViewports | ImGuiBackendFlags_HasMouseHoveredViewport);
+    io.BackendFlags &= ~(ImGuiBackendFlags_HasMouseCursors | ImGuiBackendFlags_HasSetMousePos | ImGuiBackendFlags_HasGamepad | ImGuiBackendFlags_PlatformHasViewports | ImGuiBackendFlags_HasMouseHoveredViewport | ImGuiBackendFlags_HasParentViewportId);
     platform_io.ClearPlatformHandlers();
     IM_DELETE(bd);
 }

backends/imgui_impl_win32.cpp

@@ -189,6 +189,7 @@ static bool ImGui_ImplWin32_InitEx(void* hwnd, bool platform_has_own_dc)
     io.BackendFlags |= ImGuiBackendFlags_HasSetMousePos;          // We can honor io.WantSetMousePos requests (optional, rarely used)
     io.BackendFlags |= ImGuiBackendFlags_PlatformHasViewports;    // We can create multi-viewports on the Platform side (optional)
     io.BackendFlags |= ImGuiBackendFlags_HasMouseHoveredViewport; // We can call io.AddMouseViewportEvent() with correct data (optional)
+    io.BackendFlags |= ImGuiBackendFlags_HasParentViewportId;     // We can honor viewport->ParentViewportId by applying the corresponding parent/child relationship at platform levle (optional)
 
     bd->hWnd = (HWND)hwnd;
     bd->TicksPerSecond = perf_frequency;
@@ -261,7 +262,7 @@ void    ImGui_ImplWin32_Shutdown()
 
     io.BackendPlatformName = nullptr;
     io.BackendPlatformUserData = nullptr;
-    io.BackendFlags &= ~(ImGuiBackendFlags_HasMouseCursors | ImGuiBackendFlags_HasSetMousePos | ImGuiBackendFlags_HasGamepad | ImGuiBackendFlags_PlatformHasViewports | ImGuiBackendFlags_HasMouseHoveredViewport);
+    io.BackendFlags &= ~(ImGuiBackendFlags_HasMouseCursors | ImGuiBackendFlags_HasSetMousePos | ImGuiBackendFlags_HasGamepad | ImGuiBackendFlags_PlatformHasViewports | ImGuiBackendFlags_HasMouseHoveredViewport | ImGuiBackendFlags_HasParentViewportId);
     platform_io.ClearPlatformHandlers();
     IM_DELETE(bd);
 }

docs/BACKENDS.md

@@ -182,6 +182,7 @@ The Platform backends in impl_impl_XXX.cpp files contain many implementations.
   - `ImGuiBackendFlags_HasSetMousePos`: supports io.WantSetMousePos requests to reposition the OS mouse position (only used if io.ConfigNavMoveSetMousePos is set).
   - `ImGuiBackendFlags_PlatformHasViewports` supports multiple viewports. (multi-viewports only)
   - `ImGuiBackendFlags_HasMouseHoveredViewport` supports calling io.AddMouseViewportEvent() with the viewport under the mouse. IF POSSIBLE, ignore viewports with the ImGuiViewportFlags_NoInputs flag. If this cannot be done, Dear ImGui needs to use a flawed heuristic to find the viewport under mouse position, as it doesn't know about foreign windows. (multi-viewports only)
+  - `ImGuiBackendFlags_HasParentViewportId` supports honoring viewport->ParentViewportId value, by applying the corresponding parent/child relation at the Platform level.
 
 **In your `ImGui_ImplXXX_NewFrame()` function:**
 - Set `io.DeltaTime` to the time elapsed (in seconds) since last frame.

docs/CHANGELOG.txt

@@ -105,6 +105,11 @@ Docking+Viewports Branch:
 - Nav: fixed a crash that could occur when opening a popup following the processing
   of a global shortcut while no windows were focused (the fix done in 1.92.3 was
   incomplete for docking branch).
+- Viewports: added ImGuiBackendFlags_HasParentViewportId backend flag for
+  backend to specify if it can honor the viewport->ParentViewportId value by
+  applying the corresponding parent/child relation at the Platform level. (#8948)
+  - SDL3, Win32 backends: supported.
+  - SDL2, GLFW, OSX backends: unsupported.
 - Viewports: fixed a bug where ImGuiWindowFlags_NoBringToFrontOnFocus would effectivey
   be ignored when windows first appear and viewports are enabled. (#7008) [@jshofmann]
 - Viewports: changed default value of io.ConfigViewportsNoDefaultParent to true. (#8948)

imgui.h

@@ -1785,10 +1785,11 @@ enum ImGuiBackendFlags_
     ImGuiBackendFlags_RendererHasVtxOffset  = 1 << 3,   // Backend Renderer supports ImDrawCmd::VtxOffset. This enables output of large meshes (64K+ vertices) while still using 16-bit indices.
     ImGuiBackendFlags_RendererHasTextures   = 1 << 4,   // Backend Renderer supports ImTextureData requests to create/update/destroy textures. This enables incremental texture updates and texture reloads. See https://github.com/ocornut/imgui/blob/master/docs/BACKENDS.md for instructions on how to upgrade your custom backend.
 
-    // [BETA] Viewports
-    ImGuiBackendFlags_PlatformHasViewports  = 1 << 10,  // Backend Platform supports multiple viewports.
-    ImGuiBackendFlags_HasMouseHoveredViewport=1 << 11,  // Backend Platform supports calling io.AddMouseViewportEvent() with the viewport under the mouse. IF POSSIBLE, ignore viewports with the ImGuiViewportFlags_NoInputs flag (Win32 backend, GLFW 3.30+ backend can do this, SDL backend cannot). If this cannot be done, Dear ImGui needs to use a flawed heuristic to find the viewport under.
-    ImGuiBackendFlags_RendererHasViewports  = 1 << 12,  // Backend Renderer supports multiple viewports.
+    // [BETA] Multi-Viewports
+    ImGuiBackendFlags_RendererHasViewports  = 1 << 10,  // Backend Renderer supports multiple viewports.
+    ImGuiBackendFlags_PlatformHasViewports  = 1 << 11,  // Backend Platform supports multiple viewports.
+    ImGuiBackendFlags_HasMouseHoveredViewport=1 << 12,  // Backend Platform supports calling io.AddMouseViewportEvent() with the viewport under the mouse. IF POSSIBLE, ignore viewports with the ImGuiViewportFlags_NoInputs flag (Win32 backend, GLFW 3.30+ backend can do this, SDL backend cannot). If this cannot be done, Dear ImGui needs to use a flawed heuristic to find the viewport under.
+    ImGuiBackendFlags_HasParentViewportId   = 1 << 13,  // Backend Platform supports honoring viewport->ParentViewportId value, by applying the corresponding parent/child relation at the Platform level.
 };
 
 // Enumeration for PushStyleColor() / PopStyleColor()

imgui_demo.cpp

@@ -640,6 +640,7 @@ void ImGui::ShowDemoWindow(bool* p_open)
             ImGui::CheckboxFlags("io.BackendFlags: HasSetMousePos",         &io.BackendFlags, ImGuiBackendFlags_HasSetMousePos);
             ImGui::CheckboxFlags("io.BackendFlags: PlatformHasViewports",   &io.BackendFlags, ImGuiBackendFlags_PlatformHasViewports);
             ImGui::CheckboxFlags("io.BackendFlags: HasMouseHoveredViewport",&io.BackendFlags, ImGuiBackendFlags_HasMouseHoveredViewport);
+            ImGui::CheckboxFlags("io.BackendFlags: HasParentViewportId",    &io.BackendFlags, ImGuiBackendFlags_HasParentViewportId);
             ImGui::CheckboxFlags("io.BackendFlags: RendererHasVtxOffset",   &io.BackendFlags, ImGuiBackendFlags_RendererHasVtxOffset);
             ImGui::CheckboxFlags("io.BackendFlags: RendererHasTextures",    &io.BackendFlags, ImGuiBackendFlags_RendererHasTextures);
             ImGui::CheckboxFlags("io.BackendFlags: RendererHasViewports",   &io.BackendFlags, ImGuiBackendFlags_RendererHasViewports);
@@ -8298,6 +8299,7 @@ void ImGui::ShowAboutWindow(bool* p_open)
         if (io.BackendFlags & ImGuiBackendFlags_HasSetMousePos)         ImGui::Text(" HasSetMousePos");
         if (io.BackendFlags & ImGuiBackendFlags_PlatformHasViewports)   ImGui::Text(" PlatformHasViewports");
         if (io.BackendFlags & ImGuiBackendFlags_HasMouseHoveredViewport)ImGui::Text(" HasMouseHoveredViewport");
+        if (io.BackendFlags & ImGuiBackendFlags_HasParentViewportId)    ImGui::Text(" HasParentViewportId");
         if (io.BackendFlags & ImGuiBackendFlags_RendererHasVtxOffset)   ImGui::Text(" RendererHasVtxOffset");
         if (io.BackendFlags & ImGuiBackendFlags_RendererHasTextures)    ImGui::Text(" RendererHasTextures");
         if (io.BackendFlags & ImGuiBackendFlags_RendererHasViewports)   ImGui::Text(" RendererHasViewports");