Refactor: Move viewport code under other subsystem to simplify merging (2) (moving in multiple commits to make diff/patch behave nicely)

imgui.cpp

@@ -7791,246 +7791,6 @@ ImVec2 ImGui::FindBestWindowPosForPopup(ImGuiWindow* window)
 // [SECTION] VIEWPORTS, PLATFORM WINDOWS
 //-----------------------------------------------------------------------------
 
-static void ImGui::UpdateViewportsNewFrame()
-{
-    ImGuiContext& g = *GImGui;
-    IM_ASSERT(g.PlatformIO.Viewports.Size <= g.Viewports.Size);
-
-    // Update Minimized status (we need it first in order to decide if we'll apply Pos/Size of the main viewport)
-    for (int n = 0; n < g.Viewports.Size; n++)
-    {
-        ImGuiViewportP* viewport = g.Viewports[n];
-        const bool platform_funcs_available = (n == 0 || viewport->PlatformWindowCreated);
-        if ((g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable))
-            if (g.PlatformIO.Platform_GetWindowMinimized && platform_funcs_available)
-                viewport->PlatformWindowMinimized = g.PlatformIO.Platform_GetWindowMinimized(viewport);
-    }
-
-    // Create/update main viewport with current platform position and size
-    ImGuiViewportP* main_viewport = g.Viewports[0];
-    IM_ASSERT(main_viewport->ID == IMGUI_VIEWPORT_DEFAULT_ID);
-    IM_ASSERT(main_viewport->Window == NULL);
-    ImVec2 main_viewport_platform_pos = ImVec2(0.0f, 0.0f);
-    ImVec2 main_viewport_platform_size = g.IO.DisplaySize;
-    if (g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable)
-        main_viewport_platform_pos = main_viewport->PlatformWindowMinimized ? main_viewport->Pos : g.PlatformIO.Platform_GetWindowPos(main_viewport);
-    AddUpdateViewport(NULL, IMGUI_VIEWPORT_DEFAULT_ID, main_viewport_platform_pos, main_viewport_platform_size, ImGuiViewportFlags_CanHostOtherWindows);
-
-    g.CurrentViewport = NULL;
-    g.MouseViewport = NULL;
-    for (int n = 0; n < g.Viewports.Size; n++)
-    {
-        // Erase unused viewports
-        ImGuiViewportP* viewport = g.Viewports[n];
-        viewport->Idx = n;
-
-        if (n > 0 && viewport->LastFrameActive < g.FrameCount - 2)
-        {
-            // Clear references to this viewport in windows (window->ViewportId becomes the master data)
-            for (int window_n = 0; window_n < g.Windows.Size; window_n++)
-                if (g.Windows[window_n]->Viewport == viewport)
-                {
-                    g.Windows[window_n]->Viewport = NULL;
-                    g.Windows[window_n]->ViewportOwned = false;
-                }
-            if (viewport == g.MouseLastHoveredViewport) 
-                g.MouseLastHoveredViewport = NULL;
-            g.Viewports.erase(g.Viewports.Data + n);
-
-            // Destroy
-            //IMGUI_DEBUG_LOG("Delete Viewport %08X (%s)\n", viewport->ID, viewport->Window ? viewport->Window->Name : "n/a");
-            DestroyPlatformWindow(viewport); // In most circumstances the platform window will already be destroyed here.
-            IM_ASSERT(g.PlatformIO.Viewports.contains(viewport) == false);
-            IM_DELETE(viewport);
-            n--;
-            continue;
-        }
-
-        const bool platform_funcs_available = (n == 0 || viewport->PlatformWindowCreated);
-        if ((g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable))
-        {
-            // Update Position and Size (from Platform Window to ImGui) if requested. 
-            // We do it early in the frame instead of waiting for UpdatePlatformWindows() to avoid a frame of lag when moving/resizing using OS facilities.
-            if (!viewport->PlatformWindowMinimized && platform_funcs_available)
-            {
-                if (viewport->PlatformRequestMove)
-                    viewport->Pos = viewport->LastPlatformPos = g.PlatformIO.Platform_GetWindowPos(viewport);
-                if (viewport->PlatformRequestResize)
-                    viewport->Size = viewport->LastPlatformSize = g.PlatformIO.Platform_GetWindowSize(viewport);
-            }
-
-            // Update monitor (we'll use this info to clamp windows and save windows lost in a removed monitor)
-            viewport->PlatformMonitor = (short)FindPlatformMonitorForRect(viewport->GetRect());
-        }
-
-        // Reset alpha every frame. Users of transparency (docking) needs to request a lower alpha back.
-        viewport->Alpha = 1.0f;
-
-        // Translate imgui windows when a Host Viewport has been moved
-        // (This additionally keeps windows at the same place when ImGuiConfigFlags_ViewportsEnable is toggled!)
-        ImVec2 viewport_delta = viewport->Pos - viewport->LastPos;
-        if ((viewport->Flags & ImGuiViewportFlags_CanHostOtherWindows) && (viewport_delta.x != 0.0f || viewport_delta.y != 0.0f))
-            for (int window_n = 0; window_n < g.Windows.Size; window_n++)
-                if (g.Windows[window_n]->Viewport == viewport || (g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable) == 0)
-                    TranslateWindow(g.Windows[window_n], viewport_delta);
-
-        // Update DPI scale
-        float new_dpi_scale;
-        if (g.PlatformIO.Platform_GetWindowDpiScale && platform_funcs_available)
-            new_dpi_scale = g.PlatformIO.Platform_GetWindowDpiScale(viewport);
-        else if (viewport->PlatformMonitor != -1)
-            new_dpi_scale = g.PlatformIO.Monitors[viewport->PlatformMonitor].DpiScale;
-        else
-            new_dpi_scale = (viewport->DpiScale != 0.0f) ? viewport->DpiScale : 1.0f;
-        if (viewport->DpiScale != 0.0f && new_dpi_scale != viewport->DpiScale)
-        {
-            float scale_factor = new_dpi_scale / viewport->DpiScale;
-            if (g.IO.ConfigFlags & ImGuiConfigFlags_DpiEnableScaleViewports)
-                ScaleWindowsInViewport(viewport, scale_factor);
-            //if (viewport == GetMainViewport())
-            //    g.PlatformInterface.SetWindowSize(viewport, viewport->Size * scale_factor);
-
-            // Scale our window moving pivot so that the window will rescale roughly around the mouse position.
-            // FIXME-VIEWPORT: This currently creates a resizing feedback loop when a window is straddling a DPI transition border.
-            // (Minor: since our sizes do not perfectly linearly scale, deferring the click offset scale until we know the actual window scale ratio may get us slightly more precise mouse positioning.)
-            //if (g.MovingWindow != NULL && g.MovingWindow->Viewport == viewport)
-            //    g.ActiveIdClickOffset = ImFloor(g.ActiveIdClickOffset * scale_factor);
-        }
-        viewport->DpiScale = new_dpi_scale;
-    }
-
-    if (!(g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable))
-    {
-        g.MouseViewport = main_viewport;
-        return;
-    }
-
-    // Mouse handling: decide on the actual mouse viewport for this frame between the active/focused viewport and the hovered viewport.
-    // Note that 'viewport_hovered' should skip over any viewport that has the ImGuiViewportFlags_NoInputs flags set.
-    ImGuiViewportP* viewport_hovered = NULL;
-    if (g.IO.BackendFlags & ImGuiBackendFlags_HasMouseHoveredViewport)
-    {
-        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.
-            IM_ASSERT(0);
-            viewport_hovered = FindViewportHoveredFromPlatformWindowStack(g.IO.MousePos);
-        }
-    }
-    else
-    {
-        // If the back-end doesn't know how to honor ImGuiViewportFlags_NoInputs, we do a search ourselves. Note that this search:
-        // A) won't take account of the possibility that non-imgui windows may be in-between our dragged window and our target window. 
-        // B) uses LastFrameAsRefViewport as a flawed replacement for the last time a window was focused (we could/should fix that by introducing Focus functions in PlatformIO)
-        viewport_hovered = FindViewportHoveredFromPlatformWindowStack(g.IO.MousePos);
-    }
-    if (viewport_hovered != NULL)
-        g.MouseLastHoveredViewport = viewport_hovered;
-    else if (g.MouseLastHoveredViewport == NULL)
-        g.MouseLastHoveredViewport = g.Viewports[0];
-
-    // Update mouse reference viewport
-    // (when moving a window we aim at its viewport, but this will be overwritten below if we go in drag and drop mode)
-    if (g.MovingWindow)
-        g.MouseViewport = g.MovingWindow->Viewport; 
-    else
-        g.MouseViewport = g.MouseLastHoveredViewport;
-
-    // When dragging something, always refer to the last hovered viewport. 
-    // - when releasing a moving window we will revert to aiming behind (at viewport_hovered)
-    // - when we are between viewports, our dragged preview will tend to show in the last viewport _even_ if we don't have tooltips in their viewports (when lacking monitor info)
-    // - consider the case of holding on a menu item to browse child menus: even thou a mouse button is held, there's no active id because menu items only react on mouse release.
-    const bool is_mouse_dragging_with_an_expected_destination = g.DragDropActive;
-    if (is_mouse_dragging_with_an_expected_destination && viewport_hovered == NULL)
-        viewport_hovered = g.MouseLastHoveredViewport;
-    if (is_mouse_dragging_with_an_expected_destination || g.ActiveId == 0 || !IsAnyMouseDown())
-        if (viewport_hovered != NULL && viewport_hovered != g.MouseViewport && !(viewport_hovered->Flags & ImGuiViewportFlags_NoInputs))
-            g.MouseViewport = viewport_hovered;
-
-    IM_ASSERT(g.MouseViewport != NULL);
-}
-
-// Update user-facing viewport list (g.Viewports -> g.PlatformIO.Viewports after filtering out some)
-static void ImGui::UpdateViewportsEndFrame()
-{
-    ImGuiContext& g = *GImGui;
-    g.PlatformIO.MainViewport = g.Viewports[0];
-    g.PlatformIO.Viewports.resize(0);
-    for (int i = 0; i < g.Viewports.Size; i++)
-    {
-        ImGuiViewportP* viewport = g.Viewports[i];
-        viewport->LastPos = viewport->Pos;
-        if (viewport->LastFrameActive < g.FrameCount || viewport->Size.x <= 0.0f || viewport->Size.y <= 0.0f)
-            if (i > 0) // Always include main viewport in the list
-                continue;
-        if (viewport->Window && !IsWindowActiveAndVisible(viewport->Window))
-            continue;
-        if (i > 0)
-            IM_ASSERT(viewport->Window != NULL);
-        g.PlatformIO.Viewports.push_back(viewport);
-    }
-    g.Viewports[0]->ClearRequestFlags(); // Clear main viewport flags because UpdatePlatformWindows() won't do it and may not even be called
-}
-
-// FIXME: We should ideally refactor the system to call this every frame (we currently don't)
-ImGuiViewportP* ImGui::AddUpdateViewport(ImGuiWindow* window, ImGuiID id, const ImVec2& pos, const ImVec2& size, ImGuiViewportFlags flags)
-{
-    ImGuiContext& g = *GImGui;
-    IM_ASSERT(id != 0);
-
-    if (window != NULL)
-    {
-        if (g.MovingWindow && g.MovingWindow->RootWindow == window)
-            flags |= ImGuiViewportFlags_NoInputs | ImGuiViewportFlags_NoFocusOnAppearing;
-        if ((window->Flags & ImGuiWindowFlags_NoMouseInputs) && (window->Flags & ImGuiWindowFlags_NoNavInputs))
-            flags |= ImGuiViewportFlags_NoInputs;
-        if (window->Flags & ImGuiWindowFlags_NoFocusOnAppearing)
-            flags |= ImGuiViewportFlags_NoFocusOnAppearing;
-    }
-
-    ImGuiViewportP* viewport = (ImGuiViewportP*)FindViewportByID(id);
-    if (viewport)
-    {
-        if (!viewport->PlatformRequestMove)
-            viewport->Pos = pos;
-        if (!viewport->PlatformRequestResize)
-            viewport->Size = size;
-    }
-    else
-    {
-        // New viewport
-        viewport = IM_NEW(ImGuiViewportP)();
-        viewport->ID = id;
-        viewport->Idx = g.Viewports.Size;
-        viewport->Pos = viewport->LastPos = pos;
-        viewport->Size = size;
-        viewport->PlatformMonitor = (short)FindPlatformMonitorForRect(viewport->GetRect());
-        g.Viewports.push_back(viewport);
-        //IMGUI_DEBUG_LOG("Add Viewport %08X (%s)\n", id, window->Name);
-
-        // We normally setup for all viewports in NewFrame() but here need to handle the mid-frame creation of a new viewport.
-        // We need to extend the fullscreen clip rect so the OverlayDrawList clip is correct for that the first frame
-        g.DrawListSharedData.ClipRectFullscreen.z = ImMax(g.DrawListSharedData.ClipRectFullscreen.z, viewport->Pos.x + viewport->Size.x);
-        g.DrawListSharedData.ClipRectFullscreen.w = ImMax(g.DrawListSharedData.ClipRectFullscreen.w, viewport->Pos.y + viewport->Size.y);
-
-        // Store initial DpiScale before the OS platform window creation, based on expected monitor data.
-        // This is so we can select an appropriate font size on the first frame of our window lifetime
-        if (viewport->PlatformMonitor != -1)
-            viewport->DpiScale = g.PlatformIO.Monitors[viewport->PlatformMonitor].DpiScale;
-    }
-
-    viewport->Window = window;
-    viewport->Flags = flags;
-    viewport->LastFrameActive = g.FrameCount;
-    IM_ASSERT(window == NULL || viewport->ID == window->ID);
-
-    if (window != NULL)
-        window->ViewportOwned = true;
-
-    return viewport;
-}
-
 // FIXME-VIEWPORT: This is all super messy and ought to be clarified or rewritten.
 static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
 {
@@ -8045,7 +7805,6 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
         SetWindowViewport(window, main_viewport);
         return;
     }
-
     window->ViewportOwned = false;
 
     // Appearing popups reset their viewport so they can inherit again
@@ -8138,7 +7897,6 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
             window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_NoFocusOnAppearing);
         }
     }
-
     // Regular (non-child, non-popup) windows by default are also allowed to protrude
     // Child windows are kept contained within their parent.
     else if (window->ViewportAllowPlatformMonitorExtend < 0 && (flags & ImGuiWindowFlags_ChildWindow) == 0)
@@ -8146,12 +7904,11 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
 
     // Update flags
     window->ViewportOwned = (window == window->Viewport->Window);
+    window->ViewportId = window->Viewport->ID;
 
     // If the OS window has a title bar, hide our imgui title bar
     //if (window->ViewportOwned && !(window->Viewport->Flags & ImGuiViewportFlags_NoDecoration))
     //    window->Flags |= ImGuiWindowFlags_NoTitleBar;
-
-    window->ViewportId = window->Viewport->ID;
 }
 
 // Called by user at the end of the main loop, after EndFrame()
@@ -10616,6 +10373,246 @@ static ImGuiViewportP* FindViewportHoveredFromPlatformWindowStack(const ImVec2 m
     return best_candidate;
 }
 
+static void ImGui::UpdateViewportsNewFrame()
+{
+    ImGuiContext& g = *GImGui;
+    IM_ASSERT(g.PlatformIO.Viewports.Size <= g.Viewports.Size);
+
+    // Update Minimized status (we need it first in order to decide if we'll apply Pos/Size of the main viewport)
+    for (int n = 0; n < g.Viewports.Size; n++)
+    {
+        ImGuiViewportP* viewport = g.Viewports[n];
+        const bool platform_funcs_available = (n == 0 || viewport->PlatformWindowCreated);
+        if ((g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable))
+            if (g.PlatformIO.Platform_GetWindowMinimized && platform_funcs_available)
+                viewport->PlatformWindowMinimized = g.PlatformIO.Platform_GetWindowMinimized(viewport);
+    }
+
+    // Create/update main viewport with current platform position and size
+    ImGuiViewportP* main_viewport = g.Viewports[0];
+    IM_ASSERT(main_viewport->ID == IMGUI_VIEWPORT_DEFAULT_ID);
+    IM_ASSERT(main_viewport->Window == NULL);
+    ImVec2 main_viewport_platform_pos = ImVec2(0.0f, 0.0f);
+    ImVec2 main_viewport_platform_size = g.IO.DisplaySize;
+    if (g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable)
+        main_viewport_platform_pos = main_viewport->PlatformWindowMinimized ? main_viewport->Pos : g.PlatformIO.Platform_GetWindowPos(main_viewport);
+    AddUpdateViewport(NULL, IMGUI_VIEWPORT_DEFAULT_ID, main_viewport_platform_pos, main_viewport_platform_size, ImGuiViewportFlags_CanHostOtherWindows);
+
+    g.CurrentViewport = NULL;
+    g.MouseViewport = NULL;
+    for (int n = 0; n < g.Viewports.Size; n++)
+    {
+        // Erase unused viewports
+        ImGuiViewportP* viewport = g.Viewports[n];
+        viewport->Idx = n;
+
+        if (n > 0 && viewport->LastFrameActive < g.FrameCount - 2)
+        {
+            // Clear references to this viewport in windows (window->ViewportId becomes the master data)
+            for (int window_n = 0; window_n < g.Windows.Size; window_n++)
+                if (g.Windows[window_n]->Viewport == viewport)
+                {
+                    g.Windows[window_n]->Viewport = NULL;
+                    g.Windows[window_n]->ViewportOwned = false;
+                }
+            if (viewport == g.MouseLastHoveredViewport) 
+                g.MouseLastHoveredViewport = NULL;
+            g.Viewports.erase(g.Viewports.Data + n);
+
+            // Destroy
+            //IMGUI_DEBUG_LOG("Delete Viewport %08X (%s)\n", viewport->ID, viewport->Window ? viewport->Window->Name : "n/a");
+            DestroyPlatformWindow(viewport); // In most circumstances the platform window will already be destroyed here.
+            IM_ASSERT(g.PlatformIO.Viewports.contains(viewport) == false);
+            IM_DELETE(viewport);
+            n--;
+            continue;
+        }
+
+        const bool platform_funcs_available = (n == 0 || viewport->PlatformWindowCreated);
+        if ((g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable))
+        {
+            // Update Position and Size (from Platform Window to ImGui) if requested. 
+            // We do it early in the frame instead of waiting for UpdatePlatformWindows() to avoid a frame of lag when moving/resizing using OS facilities.
+            if (!viewport->PlatformWindowMinimized && platform_funcs_available)
+            {
+                if (viewport->PlatformRequestMove)
+                    viewport->Pos = viewport->LastPlatformPos = g.PlatformIO.Platform_GetWindowPos(viewport);
+                if (viewport->PlatformRequestResize)
+                    viewport->Size = viewport->LastPlatformSize = g.PlatformIO.Platform_GetWindowSize(viewport);
+            }
+
+            // Update monitor (we'll use this info to clamp windows and save windows lost in a removed monitor)
+            viewport->PlatformMonitor = (short)FindPlatformMonitorForRect(viewport->GetRect());
+        }
+
+        // Reset alpha every frame. Users of transparency (docking) needs to request a lower alpha back.
+        viewport->Alpha = 1.0f;
+
+        // Translate imgui windows when a Host Viewport has been moved
+        // (This additionally keeps windows at the same place when ImGuiConfigFlags_ViewportsEnable is toggled!)
+        ImVec2 viewport_delta = viewport->Pos - viewport->LastPos;
+        if ((viewport->Flags & ImGuiViewportFlags_CanHostOtherWindows) && (viewport_delta.x != 0.0f || viewport_delta.y != 0.0f))
+            for (int window_n = 0; window_n < g.Windows.Size; window_n++)
+                if (g.Windows[window_n]->Viewport == viewport || (g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable) == 0)
+                    TranslateWindow(g.Windows[window_n], viewport_delta);
+
+        // Update DPI scale
+        float new_dpi_scale;
+        if (g.PlatformIO.Platform_GetWindowDpiScale && platform_funcs_available)
+            new_dpi_scale = g.PlatformIO.Platform_GetWindowDpiScale(viewport);
+        else if (viewport->PlatformMonitor != -1)
+            new_dpi_scale = g.PlatformIO.Monitors[viewport->PlatformMonitor].DpiScale;
+        else
+            new_dpi_scale = (viewport->DpiScale != 0.0f) ? viewport->DpiScale : 1.0f;
+        if (viewport->DpiScale != 0.0f && new_dpi_scale != viewport->DpiScale)
+        {
+            float scale_factor = new_dpi_scale / viewport->DpiScale;
+            if (g.IO.ConfigFlags & ImGuiConfigFlags_DpiEnableScaleViewports)
+                ScaleWindowsInViewport(viewport, scale_factor);
+            //if (viewport == GetMainViewport())
+            //    g.PlatformInterface.SetWindowSize(viewport, viewport->Size * scale_factor);
+
+            // Scale our window moving pivot so that the window will rescale roughly around the mouse position.
+            // FIXME-VIEWPORT: This currently creates a resizing feedback loop when a window is straddling a DPI transition border.
+            // (Minor: since our sizes do not perfectly linearly scale, deferring the click offset scale until we know the actual window scale ratio may get us slightly more precise mouse positioning.)
+            //if (g.MovingWindow != NULL && g.MovingWindow->Viewport == viewport)
+            //    g.ActiveIdClickOffset = ImFloor(g.ActiveIdClickOffset * scale_factor);
+        }
+        viewport->DpiScale = new_dpi_scale;
+    }
+
+    if (!(g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable))
+    {
+        g.MouseViewport = main_viewport;
+        return;
+    }
+
+    // Mouse handling: decide on the actual mouse viewport for this frame between the active/focused viewport and the hovered viewport.
+    // Note that 'viewport_hovered' should skip over any viewport that has the ImGuiViewportFlags_NoInputs flags set.
+    ImGuiViewportP* viewport_hovered = NULL;
+    if (g.IO.BackendFlags & ImGuiBackendFlags_HasMouseHoveredViewport)
+    {
+        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.
+            IM_ASSERT(0);
+            viewport_hovered = FindViewportHoveredFromPlatformWindowStack(g.IO.MousePos);
+        }
+    }
+    else
+    {
+        // If the back-end doesn't know how to honor ImGuiViewportFlags_NoInputs, we do a search ourselves. Note that this search:
+        // A) won't take account of the possibility that non-imgui windows may be in-between our dragged window and our target window. 
+        // B) uses LastFrameAsRefViewport as a flawed replacement for the last time a window was focused (we could/should fix that by introducing Focus functions in PlatformIO)
+        viewport_hovered = FindViewportHoveredFromPlatformWindowStack(g.IO.MousePos);
+    }
+    if (viewport_hovered != NULL)
+        g.MouseLastHoveredViewport = viewport_hovered;
+    else if (g.MouseLastHoveredViewport == NULL)
+        g.MouseLastHoveredViewport = g.Viewports[0];
+
+    // Update mouse reference viewport
+    // (when moving a window we aim at its viewport, but this will be overwritten below if we go in drag and drop mode)
+    if (g.MovingWindow)
+        g.MouseViewport = g.MovingWindow->Viewport; 
+    else
+        g.MouseViewport = g.MouseLastHoveredViewport;
+
+    // When dragging something, always refer to the last hovered viewport. 
+    // - when releasing a moving window we will revert to aiming behind (at viewport_hovered)
+    // - when we are between viewports, our dragged preview will tend to show in the last viewport _even_ if we don't have tooltips in their viewports (when lacking monitor info)
+    // - consider the case of holding on a menu item to browse child menus: even thou a mouse button is held, there's no active id because menu items only react on mouse release.
+    const bool is_mouse_dragging_with_an_expected_destination = g.DragDropActive;
+    if (is_mouse_dragging_with_an_expected_destination && viewport_hovered == NULL)
+        viewport_hovered = g.MouseLastHoveredViewport;
+    if (is_mouse_dragging_with_an_expected_destination || g.ActiveId == 0 || !IsAnyMouseDown())
+        if (viewport_hovered != NULL && viewport_hovered != g.MouseViewport && !(viewport_hovered->Flags & ImGuiViewportFlags_NoInputs))
+            g.MouseViewport = viewport_hovered;
+
+    IM_ASSERT(g.MouseViewport != NULL);
+}
+
+// Update user-facing viewport list (g.Viewports -> g.PlatformIO.Viewports after filtering out some)
+static void ImGui::UpdateViewportsEndFrame()
+{
+    ImGuiContext& g = *GImGui;
+    g.PlatformIO.MainViewport = g.Viewports[0];
+    g.PlatformIO.Viewports.resize(0);
+    for (int i = 0; i < g.Viewports.Size; i++)
+    {
+        ImGuiViewportP* viewport = g.Viewports[i];
+        viewport->LastPos = viewport->Pos;
+        if (viewport->LastFrameActive < g.FrameCount || viewport->Size.x <= 0.0f || viewport->Size.y <= 0.0f)
+            if (i > 0) // Always include main viewport in the list
+                continue;
+        if (viewport->Window && !IsWindowActiveAndVisible(viewport->Window))
+            continue;
+        if (i > 0)
+            IM_ASSERT(viewport->Window != NULL);
+        g.PlatformIO.Viewports.push_back(viewport);
+    }
+    g.Viewports[0]->ClearRequestFlags(); // Clear main viewport flags because UpdatePlatformWindows() won't do it and may not even be called
+}
+
+// FIXME: We should ideally refactor the system to call this every frame (we currently don't)
+ImGuiViewportP* ImGui::AddUpdateViewport(ImGuiWindow* window, ImGuiID id, const ImVec2& pos, const ImVec2& size, ImGuiViewportFlags flags)
+{
+    ImGuiContext& g = *GImGui;
+    IM_ASSERT(id != 0);
+
+    if (window != NULL)
+    {
+        if (g.MovingWindow && g.MovingWindow->RootWindow == window)
+            flags |= ImGuiViewportFlags_NoInputs | ImGuiViewportFlags_NoFocusOnAppearing;
+        if ((window->Flags & ImGuiWindowFlags_NoMouseInputs) && (window->Flags & ImGuiWindowFlags_NoNavInputs))
+            flags |= ImGuiViewportFlags_NoInputs;
+        if (window->Flags & ImGuiWindowFlags_NoFocusOnAppearing)
+            flags |= ImGuiViewportFlags_NoFocusOnAppearing;
+    }
+
+    ImGuiViewportP* viewport = (ImGuiViewportP*)FindViewportByID(id);
+    if (viewport)
+    {
+        if (!viewport->PlatformRequestMove)
+            viewport->Pos = pos;
+        if (!viewport->PlatformRequestResize)
+            viewport->Size = size;
+    }
+    else
+    {
+        // New viewport
+        viewport = IM_NEW(ImGuiViewportP)();
+        viewport->ID = id;
+        viewport->Idx = g.Viewports.Size;
+        viewport->Pos = viewport->LastPos = pos;
+        viewport->Size = size;
+        viewport->PlatformMonitor = (short)FindPlatformMonitorForRect(viewport->GetRect());
+        g.Viewports.push_back(viewport);
+        //IMGUI_DEBUG_LOG("Add Viewport %08X (%s)\n", id, window->Name);
+
+        // We normally setup for all viewports in NewFrame() but here need to handle the mid-frame creation of a new viewport.
+        // We need to extend the fullscreen clip rect so the OverlayDrawList clip is correct for that the first frame
+        g.DrawListSharedData.ClipRectFullscreen.z = ImMax(g.DrawListSharedData.ClipRectFullscreen.z, viewport->Pos.x + viewport->Size.x);
+        g.DrawListSharedData.ClipRectFullscreen.w = ImMax(g.DrawListSharedData.ClipRectFullscreen.w, viewport->Pos.y + viewport->Size.y);
+
+        // Store initial DpiScale before the OS platform window creation, based on expected monitor data.
+        // This is so we can select an appropriate font size on the first frame of our window lifetime
+        if (viewport->PlatformMonitor != -1)
+            viewport->DpiScale = g.PlatformIO.Monitors[viewport->PlatformMonitor].DpiScale;
+    }
+
+    viewport->Window = window;
+    viewport->Flags = flags;
+    viewport->LastFrameActive = g.FrameCount;
+    IM_ASSERT(window == NULL || viewport->ID == window->ID);
+
+    if (window != NULL)
+        window->ViewportOwned = true;
+
+    return viewport;
+}
+
 
 //-----------------------------------------------------------------------------
 // [SECTION] DOCKING