Viewport: Added ImGuiWindowClass / SetNextWindowClass() (concept imported from Docking ImGuiDockFamily), which currently allows to overwrite viewport flags on a per-window basis. Exposed FindViewportByID(). Win32: Support for ParentViewportId. (#1542)

examples/imgui_impl_win32.cpp

@@ -454,8 +454,11 @@ static void ImGui_ImplWin32_CreateWindow(ImGuiViewport* viewport)
     viewport->PlatformUserData = data;
 
     // Select style and parent window
-    HWND parent_window = g_hWnd;
     ImGui_ImplWin32_GetWin32StyleFromViewportFlags(viewport->Flags, &data->DwStyle, &data->DwExStyle);
+    HWND parent_window = NULL;
+    if (viewport->ParentViewportId != 0)
+        if (ImGuiViewport* parent_viewport = ImGui::FindViewportByID(viewport->ParentViewportId))
+            parent_window = (HWND)parent_viewport->PlatformHandle;
 
     // 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) };

imgui.cpp

@@ -4982,6 +4982,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
     {
         window->SizeContentsExplicit = ImVec2(0.0f, 0.0f);
     }
+    window->WindowClass = g.NextWindowData.WindowClass;
     if (g.NextWindowData.CollapsedCond)
         SetWindowCollapsed(window, g.NextWindowData.CollapsedVal, g.NextWindowData.CollapsedCond);
     if (g.NextWindowData.FocusCond)
@@ -5180,6 +5181,11 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
             if ((g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsDecoration) == 0 || (flags & (ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup)) != 0)
                 viewport_flags |= ImGuiViewportFlags_NoDecoration;
 
+            // We can overwrite viewport flags using ImGuiWindowClass (advanced users)
+            window->Viewport->ParentViewportId = window->WindowClass.ParentViewportId ? window->WindowClass.ParentViewportId : IMGUI_VIEWPORT_DEFAULT_ID;
+            if (window->WindowClass.ViewportFlagsOverrideMask)
+                viewport_flags = (viewport_flags & ~window->WindowClass.ViewportFlagsOverrideMask) | (window->WindowClass.ViewportFlagsOverrideValue & window->WindowClass.ViewportFlagsOverrideMask);
+
             // We also tell the back-end that clearing the platform window won't be necessary, as our window is filling the viewport and we have disabled BgAlpha
             viewport_flags |= ImGuiViewportFlags_NoRendererClear;
             window->Viewport->Flags = viewport_flags;
@@ -6343,6 +6349,12 @@ void ImGui::SetNextWindowViewport(ImGuiID id)
     g.NextWindowData.ViewportId = id;
 }
 
+void ImGui::SetNextWindowClass(const ImGuiWindowClass* window_class)
+{
+    ImGuiContext& g = *GImGui;
+    g.NextWindowData.WindowClass = *window_class;
+}
+
 // In window space (not screen space!)
 ImVec2 ImGui::GetContentRegionMax()
 {
@@ -7253,7 +7265,7 @@ ImGuiViewport* ImGui::GetMainViewport()
     return g.Viewports[0];
 }
 
-ImGuiViewportP* ImGui::FindViewportByID(ImGuiID id)
+ImGuiViewport* ImGui::FindViewportByID(ImGuiID id)
 {
     ImGuiContext& g = *GImGui;
     for (int n = 0; n < g.Viewports.Size; n++)
@@ -7493,7 +7505,7 @@ static void ImGui::UpdateViewportsNewFrame()
     ImGuiViewportP* viewport_hovered = NULL;
     if (g.IO.BackendFlags & ImGuiBackendFlags_HasMouseHoveredViewport)
     {
-        viewport_hovered = g.IO.MouseHoveredViewport ? FindViewportByID(g.IO.MouseHoveredViewport) : NULL;
+        viewport_hovered = g.IO.MouseHoveredViewport ? (ImGuiViewportP*)FindViewportByID(g.IO.MouseHoveredViewport) : NULL;
         if (viewport_hovered && (viewport_hovered->Flags & ImGuiViewportFlags_NoInputs))
         {
             // Back-end failed at honoring its contract if it returned a viewport with the _NoInputs flag.
@@ -7646,7 +7658,7 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
         // Attempt to restore saved viewport id (= window that hasn't been activated yet), try to restore the viewport based on saved 'window->ViewportPos' restored from .ini file
         if (window->Viewport == NULL && window->ViewportId != 0)
         {
-            window->Viewport = FindViewportByID(window->ViewportId);
+            window->Viewport = (ImGuiViewportP*)FindViewportByID(window->ViewportId);
             if (window->Viewport == NULL && window->ViewportPos.x != FLT_MAX && window->ViewportPos.y != FLT_MAX)
                 window->Viewport = AddUpdateViewport(window, window->ID, window->ViewportPos, window->Size, ImGuiViewportFlags_None);
         }
@@ -7655,7 +7667,7 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
     if (g.NextWindowData.ViewportCond)
     {
         // Code explicitly request a viewport
-        window->Viewport = FindViewportByID(g.NextWindowData.ViewportId);
+        window->Viewport = (ImGuiViewportP*)FindViewportByID(g.NextWindowData.ViewportId);
         window->ViewportId = g.NextWindowData.ViewportId; // Store ID even if Viewport isn't resolved yet.
     }
     else if ((flags & ImGuiWindowFlags_ChildWindow) || (flags & ImGuiWindowFlags_ChildMenu))

imgui.h

@@ -114,6 +114,7 @@ struct ImGuiStyle;                  // Runtime data for styling/colors
 struct ImGuiTextFilter;             // Helper to parse and apply text filters (e.g. "aaaaa[,bbbb][,ccccc]")
 struct ImGuiTextBuffer;             // Helper to hold and append into a text buffer (~string builder)
 struct ImGuiViewport;               // Viewport (generally ~1 per window to output to at the OS level. Need per-platform support to use multiple viewports)
+struct ImGuiWindowClass;            // Window class (rare/advanced uses: provide hints to the platform back-end via altered viewport flags and parent/child info)
 
 // Typedefs and Enums/Flags (declared as int for compatibility with old C++, to allow using as flags and to not pollute the top of this file)
 // Use your programming IDE "Go to definition" facility on the names of the center columns to find the actual flags/enum lists.
@@ -276,6 +277,7 @@ namespace ImGui
     IMGUI_API void          SetNextWindowFocus();                                                       // set next window to be focused / front-most. call before Begin()
     IMGUI_API void          SetNextWindowBgAlpha(float alpha);                                          // set next window background color alpha. helper to easily modify ImGuiCol_WindowBg/ChildBg/PopupBg. you may also use ImGuiWindowFlags_NoBackground.
     IMGUI_API void          SetNextWindowViewport(ImGuiID viewport_id);                                 // set next window viewport
+    IMGUI_API void          SetNextWindowClass(const ImGuiWindowClass* window_class);                   // set next window class (rare/advanced uses: provide hints to the platform back-end via altered viewport flags and parent/child info)
     IMGUI_API void          SetWindowPos(const ImVec2& pos, ImGuiCond cond = 0);                        // (not recommended) set current window position - call within Begin()/End(). prefer using SetNextWindowPos(), as this may incur tearing and side-effects.
     IMGUI_API void          SetWindowSize(const ImVec2& size, ImGuiCond cond = 0);                      // (not recommended) set current window size - call within Begin()/End(). set to ImVec2(0,0) to force an auto-fit. prefer using SetNextWindowSize(), as this may incur tearing and minor side-effects.
     IMGUI_API void          SetWindowCollapsed(bool collapsed, ImGuiCond cond = 0);                     // (not recommended) set current window collapsed state. prefer using SetNextWindowCollapsed().
@@ -688,6 +690,7 @@ namespace ImGui
     IMGUI_API void              UpdatePlatformWindows();                                        // call in main loop. will call CreateWindow/ResizeWindow/etc. platform functions for each secondary viewport, and DestroyWindow for each inactive viewport.
     IMGUI_API void              RenderPlatformWindowsDefault(void* platform_arg = NULL, void* renderer_arg = NULL); // call in main loop. will call RenderWindow/SwapBuffers platform functions for each secondary viewport. may be reimplemented by user for custom rendering needs.
     IMGUI_API void              DestroyPlatformWindows();                                       // call DestroyWindow platform functions for all viewports. call from back-end Shutdown() if you need to close platform windows before imgui shutdown. otherwise will be called by DestroyContext().
+    IMGUI_API ImGuiViewport*    FindViewportByID(ImGuiID id);                                   // this is a helper for back-ends.
     IMGUI_API ImGuiViewport*    FindViewportByPlatformHandle(void* platform_handle);            // this is a helper for back-ends. the type platform_handle is decided by the back-end (e.g. HWND, MyWindow*, GLFWwindow* etc.)
 
 } // namespace ImGui
@@ -1430,6 +1433,18 @@ struct ImGuiPayload
     bool IsDelivery() const                 { return Delivery; }
 };
 
+// [BETA] Rarely used / very advanced uses only. Use with SetNextWindowClass() function.
+// Provide hints to the platform back-end via altered viewport flags (enable/disable OS decoration, OS task bar icons, etc.) and OS level parent/child relationships.
+struct ImGuiWindowClass
+{
+    ImGuiID             ClassId;                    // User data. 0 = Default class (unclassed)
+    ImGuiID             ParentViewportId;           // Hint for the platform back-end. If non-zero, the platform back-end can create a parent<>child relationship between the platform windows. Not conforming back-ends are free to e.g. parent every viewport to the main viewport or not.
+    ImGuiViewportFlags  ViewportFlagsOverrideMask;  // Viewport flags to override when a window of this class owns a viewport. This allows you to enforce OS decoration or task bar icon, override the defaults on a per-window basis.
+    ImGuiViewportFlags  ViewportFlagsOverrideValue; // Viewport flags values to override when a window of this class owns a viewport.
+
+    ImGuiWindowClass()  { ClassId = 0; ParentViewportId = 0; ViewportFlagsOverrideMask = ViewportFlagsOverrideValue = 0x00; }
+};
+
 //-----------------------------------------------------------------------------
 // Obsolete functions (Will be removed! Read 'API BREAKING CHANGES' section in imgui.cpp for details)
 //-----------------------------------------------------------------------------
@@ -2235,6 +2250,7 @@ struct ImGuiViewport
     ImVec2              Size;                   // Size of viewport in pixel
     float               DpiScale;               // 1.0f = 96 DPI = No extra scale
     ImDrawData*         DrawData;               // The ImDrawData corresponding to this viewport. Valid after Render() and until the next call to NewFrame().
+    ImGuiID             ParentViewportId;       // (Advanced) 0: no parent. Instruct the platform back-end to setup a parent/child relationship between platform windows.
 
     void*               RendererUserData;       // void* to hold custom data structure for the renderer (e.g. swap chain, frame-buffers etc.)
     void*               PlatformUserData;       // void* to hold custom data structure for the OS / platform (e.g. windowing info, render context)
@@ -2243,7 +2259,7 @@ struct ImGuiViewport
     bool                PlatformRequestMove;    // Platform window requested move (e.g. window was moved by the OS / host window manager, authoritative position will be OS window position)
     bool                PlatformRequestResize;  // Platform window requested resize (e.g. window was resized by the OS / host window manager, authoritative size will be OS window size)
 
-    ImGuiViewport()     { ID = 0; Flags = 0; DpiScale = 0.0f; DrawData = NULL; RendererUserData = PlatformUserData = PlatformHandle = NULL; PlatformRequestClose = PlatformRequestMove = PlatformRequestResize = false; }
+    ImGuiViewport()     { ID = 0; Flags = 0; DpiScale = 0.0f; DrawData = NULL; ParentViewportId = 0; RendererUserData = PlatformUserData = PlatformHandle = NULL; PlatformRequestClose = PlatformRequestMove = PlatformRequestResize = false; }
     ~ImGuiViewport()    { IM_ASSERT(PlatformUserData == NULL && RendererUserData == NULL); }
 };
 

imgui_internal.h

@@ -714,6 +714,7 @@ struct ImGuiNextWindowData
     void*                   SizeCallbackUserData;
     float                   BgAlphaVal;
     ImGuiID                 ViewportId;
+    ImGuiWindowClass        WindowClass;
     ImVec2                  MenuBarOffsetMinVal;                // This is not exposed publicly, so we don't clear it.
 
     ImGuiNextWindowData()
@@ -733,6 +734,7 @@ struct ImGuiNextWindowData
     void    Clear()
     {
         PosCond = SizeCond = ContentSizeCond = CollapsedCond = SizeConstraintCond = FocusCond = BgAlphaCond = ViewportCond = 0;
+        WindowClass = ImGuiWindowClass();
     }
 };
 
@@ -1121,6 +1123,7 @@ struct IMGUI_API ImGuiWindow
     char*                   Name;
     ImGuiID                 ID;                                 // == ImHash(Name)
     ImGuiWindowFlags        Flags, FlagsPreviousFrame;          // See enum ImGuiWindowFlags_
+    ImGuiWindowClass        WindowClass;                        // Advanced users only. Set with SetNextWindowClass()
     ImGuiViewportP*         Viewport;                           // Always set in Begin(), only inactive windows may have a NULL value here
     ImGuiID                 ViewportId;                         // We backup the viewport id (since the viewport may disappear or never be created if the window is inactive)
     ImVec2                  ViewportPos;                        // We backup the viewport position (since the viewport may disappear or never be created if the window is inactive)
@@ -1331,7 +1334,6 @@ namespace ImGui
     IMGUI_API void          UpdateMouseMovingWindow();
 
     // Viewports
-    IMGUI_API ImGuiViewportP*       FindViewportByID(ImGuiID id);
     IMGUI_API void                  ScaleWindowsInViewport(ImGuiViewportP* viewport, float scale);
     IMGUI_API void                  DestroyPlatformWindow(ImGuiViewportP* viewport);
     IMGUI_API void                  ShowViewportThumbnails();