diff --git a/imgui.cpp b/imgui.cpp
index 807aadb..3455a15 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -759,7 +759,6 @@
 
 // Viewports
 const ImGuiID           IMGUI_VIEWPORT_DEFAULT_ID = 0x11111111; // Using an arbitrary constant instead of e.g. ImHash("ViewportDefault", 0); so it's easier to spot in the debugger. The exact value doesn't matter.
-static inline ImRect    GetViewportRect(ImGuiWindow* window) { return window->Viewport->GetRect(); }
 static inline ImVec2    ConvertViewportPosToPlatformPos(const ImVec2& imgui_pos, ImGuiViewport* viewport)    { return imgui_pos - viewport->Pos + viewport->PlatformPos; }
 static inline ImVec2    ConvertPlatformPosToViewportPos(const ImVec2& platform_pos, ImGuiViewport* viewport) { return platform_pos - viewport->PlatformPos + viewport->Pos; }
 static ImGuiViewportP*  AddUpdateViewport(ImGuiWindow* window, ImGuiID id, ImGuiViewportFlags flags, const ImVec2& platform_pos, const ImVec2& size);
@@ -2147,7 +2146,7 @@
             }
 
     // Filter by viewport
-    if (window->Viewport != g.MousePosViewport)
+    if (window->Viewport != g.MouseRefViewport)
         return false;
 
     return true;
@@ -2775,12 +2774,11 @@
 static ImVec2 NavCalcPreferredMousePos()
 {
     ImGuiContext& g = *GImGui;
-    ImGuiWindow* window = g.NavWindow;
-    if (!window)
+    if (!g.NavWindow)
         return g.IO.MousePos;
-    const ImRect& rect_rel = window->NavRectRel[g.NavLayer];
+    const ImRect& rect_rel = g.NavWindow->NavRectRel[g.NavLayer];
     ImVec2 pos = g.NavWindow->Pos + ImVec2(rect_rel.Min.x + ImMin(g.Style.FramePadding.x*4, rect_rel.GetWidth()), rect_rel.Max.y - ImMin(g.Style.FramePadding.y, rect_rel.GetHeight()));
-    ImRect visible_rect = ImGui::GetViewportRect(window);
+    ImRect visible_rect = g.NavWindow->Viewport->GetRect();
     return ImFloor(ImClamp(pos, visible_rect.Min, visible_rect.Max));   // ImFloor() is important because non-integer mouse position application in back-end might be lossy and result in undesirable non-zero delta.
 }
 
@@ -3307,20 +3305,20 @@
     if (!(g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable))
         return;
 
-    ImRect mouse_viewport_rect = g.MousePosViewport->GetRect();
-    ImVec2 window_pos_in_mouse_viewport = ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(window->Pos, window->Viewport), g.MousePosViewport);
+    ImRect mouse_viewport_rect = g.MouseRefViewport->GetRect();
+    ImVec2 window_pos_in_mouse_viewport = ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(window->Pos, window->Viewport), g.MouseRefViewport);
     ImRect window_rect_in_mouse_viewport = ImRect(window_pos_in_mouse_viewport, window_pos_in_mouse_viewport + window->Size);
-    if ((g.MousePosViewport->Flags & ImGuiViewportFlags_CanHostOtherWindows) && mouse_viewport_rect.Contains(window_rect_in_mouse_viewport))
+    if ((g.MouseRefViewport->Flags & ImGuiViewportFlags_CanHostOtherWindows) && mouse_viewport_rect.Contains(window_rect_in_mouse_viewport))
     {
         // Drop on an existing viewport
         ImGuiViewportP* old_viewport = window->Viewport;
-        SetWindowViewportTranslateToPreservePlatformPos(window, window->Viewport, g.MousePosViewport);
+        SetWindowViewportTranslateToPreservePlatformPos(window, window->Viewport, g.MouseRefViewport);
 
         // Move child/hosted windows as well (FIXME-OPT)
         if (window->ViewportOwned)
             for (int n = 0; n < g.Windows.Size; n++)
                 if (g.Windows[n]->Viewport == old_viewport)
-                    SetWindowViewportTranslateToPreservePlatformPos(g.Windows[n], old_viewport, g.MousePosViewport);
+                    SetWindowViewportTranslateToPreservePlatformPos(g.Windows[n], old_viewport, g.MouseRefViewport);
         window->ViewportOwned = false;
     }
     else
@@ -3421,9 +3419,9 @@
 
             // Destroy
             if (viewport == viewport_ref)               viewport_ref = NULL;
-            if (viewport == g.MousePosViewport)         g.MousePosViewport = NULL;
-            if (viewport == g.MousePosPrevViewport)     g.MousePosPrevViewport = NULL;
-            if (viewport == g.MouseHoveredPrevViewport) g.MouseHoveredPrevViewport = NULL;
+            if (viewport == g.MouseRefViewport)         g.MouseRefViewport = NULL;
+            if (viewport == g.MouseRefPrevViewport)     g.MouseRefPrevViewport = NULL;
+            if (viewport == g.MouseHoveredLastViewport) g.MouseHoveredLastViewport = NULL;
             IM_ASSERT(viewport->RendererUserData == NULL && viewport->PlatformUserData == NULL && viewport->PlatformHandle == NULL);
             IM_ASSERT(g.PlatformIO.Viewports.contains(viewport) == false);
             IM_DELETE(viewport);
@@ -3478,7 +3476,7 @@
 
     if (!(g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable))
     {
-        g.MousePosViewport = g.MousePosPrevViewport = main_viewport;
+        g.MouseRefViewport = g.MouseRefPrevViewport = main_viewport;
         return;
     }
 
@@ -3496,12 +3494,13 @@
     }
     else
     {
-        // If the back-end doesn't set MouseLastHoveredViewport or doesn't honor ImGuiViewportFlags_NoInputs, we do a search ourselves.
-        // This search won't take account of the possibility that non-imgui windows may be in-between our dragged window and our target window.
+        // 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(mouse_platform_pos);
     }
     if (viewport_hovered != NULL)
-        g.MouseHoveredPrevViewport = viewport_hovered;
+        g.MouseHoveredLastViewport = viewport_hovered;
 
     // If reference viewport just has been deleted, use a position relative to the main viewport
     if (viewport_ref == NULL)
@@ -3510,9 +3509,9 @@
         g.IO.MousePos = ConvertPlatformPosToViewportPos(mouse_platform_pos, viewport_ref);
     }
 
-    g.MousePosPrevViewport = g.MousePosViewport;
-    g.MousePosViewport = viewport_ref;
-    g.MousePosViewport->LastFrameAsRefViewport = g.FrameCount;
+    g.MouseRefPrevViewport = g.MouseRefViewport;
+    g.MouseRefViewport = viewport_ref;
+    g.MouseRefViewport->LastFrameAsRefViewport = g.FrameCount;
 
     // When dragging something, always refer to the last hovered viewport (so when we are between viewport, our dragged preview will tend to show in the last viewport)
     const bool is_mouse_dragging_with_an_expected_destination = g.DragDropActive || (g.MovingWindow != NULL);
@@ -3520,15 +3519,15 @@
     if (is_mouse_dragging_with_an_expected_destination || is_mouse_all_released)
     {
         if (is_mouse_dragging_with_an_expected_destination)
-            viewport_hovered = g.MouseHoveredPrevViewport;
-        if (viewport_hovered != NULL && viewport_hovered != g.MousePosViewport && !(viewport_hovered->Flags & ImGuiViewportFlags_NoInputs))
+            viewport_hovered = g.MouseHoveredLastViewport;
+        if (viewport_hovered != NULL && viewport_hovered != g.MouseRefViewport && !(viewport_hovered->Flags & ImGuiViewportFlags_NoInputs))
         {
-            g.IO.MousePos = ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(g.IO.MousePos, g.MousePosViewport), viewport_hovered);
-            g.MousePosViewport = viewport_hovered;
+            g.IO.MousePos = ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(g.IO.MousePos, g.MouseRefViewport), viewport_hovered);
+            g.MouseRefViewport = viewport_hovered;
         }
     }
 
-    IM_ASSERT(g.MousePosViewport != NULL);
+    IM_ASSERT(g.MouseRefViewport != NULL);
 }
 
 void ImGui::UpdatePlatformWindows()
@@ -3594,7 +3593,7 @@
 
         // Update title bar
         const char* title_begin = viewport->Window->Name;
-        char* title_end = (char*)ImGui::FindRenderedTextEnd(title_begin);
+        char* title_end = (char*)(intptr_t)ImGui::FindRenderedTextEnd(title_begin);
         const ImGuiID title_hash = ImHash(title_begin, (int)(title_end - title_begin));
         if (viewport->LastNameHash != title_hash)
         {
@@ -3659,7 +3658,7 @@
     ImGuiContext& g = *GImGui;
 
     // If mouse just appeared or disappeared (usually denoted by -FLT_MAX component, but in reality we test for -256000.0f) we cancel out movement in MouseDelta
-    if (ImGui::IsMousePosValid(&g.IO.MousePos) && ImGui::IsMousePosValid(&g.IO.MousePosPrev) && g.MousePosViewport == g.MousePosPrevViewport)
+    if (ImGui::IsMousePosValid(&g.IO.MousePos) && ImGui::IsMousePosValid(&g.IO.MousePosPrev) && g.MouseRefViewport == g.MouseRefPrevViewport)
         g.IO.MouseDelta = g.IO.MousePos - g.IO.MousePosPrev;
     else
         g.IO.MouseDelta = ImVec2(0.0f, 0.0f);
@@ -3689,7 +3688,7 @@
             g.IO.MouseClickedPos[i] = g.IO.MousePos;
             g.IO.MouseDragMaxDistanceAbs[i] = ImVec2(0.0f, 0.0f);
             g.IO.MouseDragMaxDistanceSqr[i] = 0.0f;
-            g.MouseClickedPosViewportId[i] = g.MousePosViewport->ID;
+            g.MouseClickedPosViewportId[i] = g.MouseRefViewport->ID;
         }
         else if (g.IO.MouseDown[i])
         {
@@ -3714,7 +3713,7 @@
     // - We also support the moved window toggling the NoInputs flag after moving has started in order to be able to detect windows below it, which is useful for e.g. docking mechanisms.
     g.HoveredWindow = (g.MovingWindow && !(g.MovingWindow->Flags & ImGuiWindowFlags_NoInputs)) ? g.MovingWindow : FindHoveredWindow();
     g.HoveredRootWindow = g.HoveredWindow ? g.HoveredWindow->RootWindow : NULL;
-    IM_ASSERT(g.HoveredWindow == NULL || g.HoveredWindow == g.MovingWindow || g.HoveredWindow->Viewport == g.MousePosViewport);
+    IM_ASSERT(g.HoveredWindow == NULL || g.HoveredWindow == g.MovingWindow || g.HoveredWindow->Viewport == g.MouseRefViewport);
 
     // Modal windows prevents cursor from hovering behind them.
     ImGuiWindow* modal_window = GetFrontMostPopupModal();
@@ -4127,7 +4126,7 @@
     g.FontStack.clear();
     g.OpenPopupStack.clear();
     g.CurrentPopupStack.clear();
-    g.CurrentViewport = g.MousePosViewport = g.MousePosPrevViewport = g.MouseHoveredPrevViewport = NULL;
+    g.CurrentViewport = g.MouseRefViewport = g.MouseRefPrevViewport = g.MouseHoveredLastViewport = NULL;
     for (int i = 0; i < g.Viewports.Size; i++)
         IM_DELETE(g.Viewports[i]);
     g.Viewports.clear();
@@ -4575,7 +4574,7 @@
         for (int viewport_n = 0; viewport_n < g.Viewports.Size; viewport_n++)
         {
             ImGuiViewportP* viewport = g.Viewports[viewport_n];
-            ImVec2 pos = (g.MousePosViewport == viewport) ? main_pos : ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(main_pos, g.MousePosViewport), viewport);
+            ImVec2 pos = (g.MouseRefViewport == viewport) ? main_pos : ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(main_pos, g.MouseRefViewport), viewport);
             if (viewport->GetRect().Overlaps(ImRect(pos, pos + ImVec2(2,2)*sc + size * sc)))
             {
                 ImDrawList* draw_list = GetOverlayDrawList(viewport);
@@ -4674,7 +4673,7 @@
         ImGuiID viewport_id = viewport->ID;
         if (viewport_id == g.IO.MousePosViewport)  // We are early in NewFrame and g.MousePosViewport hasn't been set, patch the source.
             g.IO.MousePos.x += delta_x;
-        if (viewport == g.MousePosPrevViewport)
+        if (viewport == g.MouseRefPrevViewport)
             g.IO.MousePosPrev.x += delta_x;
         for (int mouse_n = 0; mouse_n < IM_ARRAYSIZE(g.MouseClickedPosViewportId); mouse_n++)
             if (g.MouseClickedPosViewportId[mouse_n] == viewport_id)
@@ -5106,7 +5105,7 @@
         if (window->Flags & ImGuiWindowFlags_NoInputs)
             continue;
         IM_ASSERT(window->Viewport);
-        if (window->Viewport != g.MousePosViewport)
+        if (window->Viewport != g.MouseRefViewport)
             continue;
 
         // Using the clipped AABB, a child window will typically be clipped by its parent (not always)
@@ -5134,7 +5133,7 @@
     const ImRect rect_for_touch(rect_clipped.Min - g.Style.TouchExtraPadding, rect_clipped.Max + g.Style.TouchExtraPadding);
     if (!rect_for_touch.Contains(g.IO.MousePos))
         return false;
-    if (!g.MousePosViewport->GetRect().Overlaps(rect_clipped))
+    if (!g.MouseRefViewport->GetRect().Overlaps(rect_clipped))
         return false;
     return true;
 }
@@ -5290,7 +5289,7 @@
         lock_threshold = g.IO.MouseDragThreshold;
     if (g.IO.MouseDown[button])
         if (g.IO.MouseDragMaxDistanceSqr[button] >= lock_threshold * lock_threshold)
-            if (g.MousePosViewport->ID == g.MouseClickedPosViewportId[button])
+            if (g.MouseRefViewport->ID == g.MouseClickedPosViewportId[button])
                 return g.IO.MousePos - g.IO.MouseClickedPos[button];     // Assume we can only get active with left-mouse button (at the moment).
     return ImVec2(0.0f, 0.0f);
 }
@@ -5623,7 +5622,7 @@
     // Center modal windows by default
     // FIXME: Should test for (PosCond & window->SetWindowPosAllowFlags) with the upcoming window.
     if (g.NextWindowData.PosCond == 0)
-        SetNextWindowPos(GetViewportRect(window).GetCenter(), ImGuiCond_Appearing, ImVec2(0.5f, 0.5f));
+        SetNextWindowPos(window->Viewport->GetCenter(), ImGuiCond_Appearing, ImVec2(0.5f, 0.5f));
 
     bool is_open = Begin(name, p_open, flags | ImGuiWindowFlags_Popup | ImGuiWindowFlags_Modal | ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoSavedSettings);
     if (!is_open || (p_open && !*p_open)) // NB: is_open can be 'false' when the popup is completely clipped (e.g. zero size display)
@@ -5848,7 +5847,7 @@
 static ImRect FindScreenRectForWindow(ImGuiWindow* window)
 {
     ImVec2 padding = GImGui->Style.DisplaySafeAreaPadding;
-    ImRect r_screen(ImGui::GetViewportRect(window));
+    ImRect r_screen(window->Viewport->GetRect());
     r_screen.Expand(ImVec2((window->Size.x - r_screen.GetWidth() > padding.x * 2) ? -padding.x : 0.0f, (window->Size.y - r_screen.GetHeight() > padding.y * 2) ? -padding.y : 0.0f));
     return r_screen;
 }
@@ -5927,11 +5926,13 @@
             r_avoid = ImRect(parent_menu->Pos.x + horizontal_overlap, -FLT_MAX, parent_menu->Pos.x + parent_menu->Size.x - horizontal_overlap - parent_menu->ScrollbarSizes.x, FLT_MAX);
         return FindBestWindowPosForPopupEx(window->PosFloat, window->Size, &window->AutoPosLastDirection, r_screen, r_avoid);
     }
+
     if (window->Flags & ImGuiWindowFlags_Popup)
     {
         ImRect r_avoid(window->PosFloat.x - 1, window->PosFloat.y - 1, window->PosFloat.x + 1, window->PosFloat.y + 1);
         return FindBestWindowPosForPopupEx(window->PosFloat, window->Size, &window->AutoPosLastDirection, r_screen, r_avoid);
     }
+
     if (window->Flags & ImGuiWindowFlags_Tooltip)
     {
         // Position tooltip (always follows mouse)
@@ -6060,25 +6061,25 @@
 {
     ImGuiContext& g = *GImGui;
     ImGuiStyle& style = g.Style;
-    ImGuiWindowFlags flags = window->Flags;
-    ImVec2 size_auto_fit;
-    if ((flags & ImGuiWindowFlags_Tooltip) != 0)
+    if (window->Flags & ImGuiWindowFlags_Tooltip)
     {
-        // Tooltip always resize. We keep the spacing symmetric on both axises for aesthetic purpose.
-        size_auto_fit = size_contents;
+        // Tooltip always resize
+        return size_contents;
     }
     else
     {
-        // When the window cannot fit all contents (either because of constraints, either because screen is too small): we are growing the size on the other axis to compensate for expected scrollbar. FIXME: Might turn bigger than ViewportSize-WindowPadding.
-        ImVec2 viewport_size = window->ViewportOwned ? ImVec2(FLT_MAX, FLT_MAX) : window->Viewport->Size;
-        size_auto_fit = ImClamp(size_contents, style.WindowMinSize, ImMax(style.WindowMinSize, viewport_size - g.Style.DisplaySafeAreaPadding));
+        ImVec2 avail_size = window->ViewportOwned ? ImVec2(FLT_MAX, FLT_MAX) : window->Viewport->Size;
+        ImVec2 size_auto_fit = ImClamp(size_contents, style.WindowMinSize, ImMax(style.WindowMinSize, avail_size - g.Style.DisplaySafeAreaPadding));
+
+        // When the window cannot fit all contents (either because of constraints, either because screen is too small),
+        // we are growing the size on the other axis to compensate for expected scrollbar. FIXME: Might turn bigger than ViewportSize-WindowPadding.
         ImVec2 size_auto_fit_after_constraint = CalcSizeAfterConstraint(window, size_auto_fit);
-        if (size_auto_fit_after_constraint.x < size_contents.x && !(flags & ImGuiWindowFlags_NoScrollbar) && (flags & ImGuiWindowFlags_HorizontalScrollbar))
+        if (size_auto_fit_after_constraint.x < size_contents.x && !(window->Flags & ImGuiWindowFlags_NoScrollbar) && (window->Flags & ImGuiWindowFlags_HorizontalScrollbar))
             size_auto_fit.y += style.ScrollbarSize;
-        if (size_auto_fit_after_constraint.y < size_contents.y && !(flags & ImGuiWindowFlags_NoScrollbar))
+        if (size_auto_fit_after_constraint.y < size_contents.y && !(window->Flags & ImGuiWindowFlags_NoScrollbar))
             size_auto_fit.x += style.ScrollbarSize;
+        return size_auto_fit;
     }
-    return size_auto_fit;
 }
 
 static float GetScrollMaxX(ImGuiWindow* window)
@@ -6201,6 +6202,7 @@
     }
     else if (flags & ImGuiWindowFlags_ChildWindow)
     {
+        // Inherit viewport from parent window
         window->Viewport = window->ParentWindow->Viewport;
     }
     else if (window_follow_mouse_viewport && IsMousePosValid())
@@ -6211,7 +6213,7 @@
         if (!window_is_mouse_tooltip && (current_viewport == NULL || !current_viewport->GetRect().Contains(window->Rect())))
         {
             // Calculate mouse position in OS/platform coordinates, create a Viewport at this position.
-            ImVec2 platform_pos = ConvertViewportPosToPlatformPos(g.IO.MousePos - g.ActiveIdClickOffset, g.MousePosViewport);
+            ImVec2 platform_pos = ConvertViewportPosToPlatformPos(g.IO.MousePos - g.ActiveIdClickOffset, g.MouseRefViewport);
             ImGuiViewportFlags viewport_flags = ImGuiViewportFlags_NoDecoration | ImGuiViewportFlags_NoFocusOnAppearing | ImGuiViewportFlags_NoInputs;
             ImGuiViewportP* viewport = AddUpdateViewport(window, window->ID, viewport_flags, platform_pos, window->Size);
             window->Viewport = viewport;
@@ -6219,7 +6221,7 @@
         }
         else
         {
-            window->Viewport = g.MousePosViewport;
+            window->Viewport = g.MouseRefViewport;
         }
     }
     else if (g.NavWindow != NULL && g.NavWindow != window && (flags & ImGuiWindowFlags_Tooltip))
@@ -6231,7 +6233,7 @@
     if (window->Viewport == NULL)
         window->Viewport = main_viewport;
 
-    // When we own the viewport update its size
+    // When we own the viewport update its size/position
     if (window == window->Viewport->Window && !created_viewport)
     {
         window->Viewport->Flags |= ImGuiViewportFlags_NoDecoration;
@@ -6671,7 +6673,7 @@
 
         // Clamp position so window stays visible within its viewport
         // Ignore zero-sized display explicitly to avoid losing positions if a window manager reports zero-sized window when initializing or minimizing.
-        ImRect viewport_rect(GetViewportRect(window));
+        ImRect viewport_rect = window->Viewport->GetRect();
         if (!window_pos_set_by_api && !(flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_Tooltip)) && !window->ViewportOwned && window->AutoFitFramesX <= 0 && window->AutoFitFramesY <= 0)
             if (viewport_rect.GetWidth() > 0 && viewport_rect.GetHeight() > 0.0f)
             {
@@ -6727,7 +6729,7 @@
         if (window->ViewportOwned && (window->Size.x != window->Viewport->Size.x || window->Size.y != window->Viewport->Size.y))
         {
             window->Viewport->Size = window->SizeFull;
-            viewport_rect = GetViewportRect(window);
+            viewport_rect = window->Viewport->GetRect();
         }
 
         // DRAWING

diff --git a/imgui.cpp b/imgui.cpp
index 807aadb..3455a15 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -759,7 +759,6 @@
 
 // Viewports
 const ImGuiID           IMGUI_VIEWPORT_DEFAULT_ID = 0x11111111; // Using an arbitrary constant instead of e.g. ImHash("ViewportDefault", 0); so it's easier to spot in the debugger. The exact value doesn't matter.
-static inline ImRect    GetViewportRect(ImGuiWindow* window) { return window->Viewport->GetRect(); }
 static inline ImVec2    ConvertViewportPosToPlatformPos(const ImVec2& imgui_pos, ImGuiViewport* viewport)    { return imgui_pos - viewport->Pos + viewport->PlatformPos; }
 static inline ImVec2    ConvertPlatformPosToViewportPos(const ImVec2& platform_pos, ImGuiViewport* viewport) { return platform_pos - viewport->PlatformPos + viewport->Pos; }
 static ImGuiViewportP*  AddUpdateViewport(ImGuiWindow* window, ImGuiID id, ImGuiViewportFlags flags, const ImVec2& platform_pos, const ImVec2& size);
@@ -2147,7 +2146,7 @@
             }
 
     // Filter by viewport
-    if (window->Viewport != g.MousePosViewport)
+    if (window->Viewport != g.MouseRefViewport)
         return false;
 
     return true;
@@ -2775,12 +2774,11 @@
 static ImVec2 NavCalcPreferredMousePos()
 {
     ImGuiContext& g = *GImGui;
-    ImGuiWindow* window = g.NavWindow;
-    if (!window)
+    if (!g.NavWindow)
         return g.IO.MousePos;
-    const ImRect& rect_rel = window->NavRectRel[g.NavLayer];
+    const ImRect& rect_rel = g.NavWindow->NavRectRel[g.NavLayer];
     ImVec2 pos = g.NavWindow->Pos + ImVec2(rect_rel.Min.x + ImMin(g.Style.FramePadding.x*4, rect_rel.GetWidth()), rect_rel.Max.y - ImMin(g.Style.FramePadding.y, rect_rel.GetHeight()));
-    ImRect visible_rect = ImGui::GetViewportRect(window);
+    ImRect visible_rect = g.NavWindow->Viewport->GetRect();
     return ImFloor(ImClamp(pos, visible_rect.Min, visible_rect.Max));   // ImFloor() is important because non-integer mouse position application in back-end might be lossy and result in undesirable non-zero delta.
 }
 
@@ -3307,20 +3305,20 @@
     if (!(g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable))
         return;
 
-    ImRect mouse_viewport_rect = g.MousePosViewport->GetRect();
-    ImVec2 window_pos_in_mouse_viewport = ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(window->Pos, window->Viewport), g.MousePosViewport);
+    ImRect mouse_viewport_rect = g.MouseRefViewport->GetRect();
+    ImVec2 window_pos_in_mouse_viewport = ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(window->Pos, window->Viewport), g.MouseRefViewport);
     ImRect window_rect_in_mouse_viewport = ImRect(window_pos_in_mouse_viewport, window_pos_in_mouse_viewport + window->Size);
-    if ((g.MousePosViewport->Flags & ImGuiViewportFlags_CanHostOtherWindows) && mouse_viewport_rect.Contains(window_rect_in_mouse_viewport))
+    if ((g.MouseRefViewport->Flags & ImGuiViewportFlags_CanHostOtherWindows) && mouse_viewport_rect.Contains(window_rect_in_mouse_viewport))
     {
         // Drop on an existing viewport
         ImGuiViewportP* old_viewport = window->Viewport;
-        SetWindowViewportTranslateToPreservePlatformPos(window, window->Viewport, g.MousePosViewport);
+        SetWindowViewportTranslateToPreservePlatformPos(window, window->Viewport, g.MouseRefViewport);
 
         // Move child/hosted windows as well (FIXME-OPT)
         if (window->ViewportOwned)
             for (int n = 0; n < g.Windows.Size; n++)
                 if (g.Windows[n]->Viewport == old_viewport)
-                    SetWindowViewportTranslateToPreservePlatformPos(g.Windows[n], old_viewport, g.MousePosViewport);
+                    SetWindowViewportTranslateToPreservePlatformPos(g.Windows[n], old_viewport, g.MouseRefViewport);
         window->ViewportOwned = false;
     }
     else
@@ -3421,9 +3419,9 @@
 
             // Destroy
             if (viewport == viewport_ref)               viewport_ref = NULL;
-            if (viewport == g.MousePosViewport)         g.MousePosViewport = NULL;
-            if (viewport == g.MousePosPrevViewport)     g.MousePosPrevViewport = NULL;
-            if (viewport == g.MouseHoveredPrevViewport) g.MouseHoveredPrevViewport = NULL;
+            if (viewport == g.MouseRefViewport)         g.MouseRefViewport = NULL;
+            if (viewport == g.MouseRefPrevViewport)     g.MouseRefPrevViewport = NULL;
+            if (viewport == g.MouseHoveredLastViewport) g.MouseHoveredLastViewport = NULL;
             IM_ASSERT(viewport->RendererUserData == NULL && viewport->PlatformUserData == NULL && viewport->PlatformHandle == NULL);
             IM_ASSERT(g.PlatformIO.Viewports.contains(viewport) == false);
             IM_DELETE(viewport);
@@ -3478,7 +3476,7 @@
 
     if (!(g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable))
     {
-        g.MousePosViewport = g.MousePosPrevViewport = main_viewport;
+        g.MouseRefViewport = g.MouseRefPrevViewport = main_viewport;
         return;
     }
 
@@ -3496,12 +3494,13 @@
     }
     else
     {
-        // If the back-end doesn't set MouseLastHoveredViewport or doesn't honor ImGuiViewportFlags_NoInputs, we do a search ourselves.
-        // This search won't take account of the possibility that non-imgui windows may be in-between our dragged window and our target window.
+        // 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(mouse_platform_pos);
     }
     if (viewport_hovered != NULL)
-        g.MouseHoveredPrevViewport = viewport_hovered;
+        g.MouseHoveredLastViewport = viewport_hovered;
 
     // If reference viewport just has been deleted, use a position relative to the main viewport
     if (viewport_ref == NULL)
@@ -3510,9 +3509,9 @@
         g.IO.MousePos = ConvertPlatformPosToViewportPos(mouse_platform_pos, viewport_ref);
     }
 
-    g.MousePosPrevViewport = g.MousePosViewport;
-    g.MousePosViewport = viewport_ref;
-    g.MousePosViewport->LastFrameAsRefViewport = g.FrameCount;
+    g.MouseRefPrevViewport = g.MouseRefViewport;
+    g.MouseRefViewport = viewport_ref;
+    g.MouseRefViewport->LastFrameAsRefViewport = g.FrameCount;
 
     // When dragging something, always refer to the last hovered viewport (so when we are between viewport, our dragged preview will tend to show in the last viewport)
     const bool is_mouse_dragging_with_an_expected_destination = g.DragDropActive || (g.MovingWindow != NULL);
@@ -3520,15 +3519,15 @@
     if (is_mouse_dragging_with_an_expected_destination || is_mouse_all_released)
     {
         if (is_mouse_dragging_with_an_expected_destination)
-            viewport_hovered = g.MouseHoveredPrevViewport;
-        if (viewport_hovered != NULL && viewport_hovered != g.MousePosViewport && !(viewport_hovered->Flags & ImGuiViewportFlags_NoInputs))
+            viewport_hovered = g.MouseHoveredLastViewport;
+        if (viewport_hovered != NULL && viewport_hovered != g.MouseRefViewport && !(viewport_hovered->Flags & ImGuiViewportFlags_NoInputs))
         {
-            g.IO.MousePos = ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(g.IO.MousePos, g.MousePosViewport), viewport_hovered);
-            g.MousePosViewport = viewport_hovered;
+            g.IO.MousePos = ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(g.IO.MousePos, g.MouseRefViewport), viewport_hovered);
+            g.MouseRefViewport = viewport_hovered;
         }
     }
 
-    IM_ASSERT(g.MousePosViewport != NULL);
+    IM_ASSERT(g.MouseRefViewport != NULL);
 }
 
 void ImGui::UpdatePlatformWindows()
@@ -3594,7 +3593,7 @@
 
         // Update title bar
         const char* title_begin = viewport->Window->Name;
-        char* title_end = (char*)ImGui::FindRenderedTextEnd(title_begin);
+        char* title_end = (char*)(intptr_t)ImGui::FindRenderedTextEnd(title_begin);
         const ImGuiID title_hash = ImHash(title_begin, (int)(title_end - title_begin));
         if (viewport->LastNameHash != title_hash)
         {
@@ -3659,7 +3658,7 @@
     ImGuiContext& g = *GImGui;
 
     // If mouse just appeared or disappeared (usually denoted by -FLT_MAX component, but in reality we test for -256000.0f) we cancel out movement in MouseDelta
-    if (ImGui::IsMousePosValid(&g.IO.MousePos) && ImGui::IsMousePosValid(&g.IO.MousePosPrev) && g.MousePosViewport == g.MousePosPrevViewport)
+    if (ImGui::IsMousePosValid(&g.IO.MousePos) && ImGui::IsMousePosValid(&g.IO.MousePosPrev) && g.MouseRefViewport == g.MouseRefPrevViewport)
         g.IO.MouseDelta = g.IO.MousePos - g.IO.MousePosPrev;
     else
         g.IO.MouseDelta = ImVec2(0.0f, 0.0f);
@@ -3689,7 +3688,7 @@
             g.IO.MouseClickedPos[i] = g.IO.MousePos;
             g.IO.MouseDragMaxDistanceAbs[i] = ImVec2(0.0f, 0.0f);
             g.IO.MouseDragMaxDistanceSqr[i] = 0.0f;
-            g.MouseClickedPosViewportId[i] = g.MousePosViewport->ID;
+            g.MouseClickedPosViewportId[i] = g.MouseRefViewport->ID;
         }
         else if (g.IO.MouseDown[i])
         {
@@ -3714,7 +3713,7 @@
     // - We also support the moved window toggling the NoInputs flag after moving has started in order to be able to detect windows below it, which is useful for e.g. docking mechanisms.
     g.HoveredWindow = (g.MovingWindow && !(g.MovingWindow->Flags & ImGuiWindowFlags_NoInputs)) ? g.MovingWindow : FindHoveredWindow();
     g.HoveredRootWindow = g.HoveredWindow ? g.HoveredWindow->RootWindow : NULL;
-    IM_ASSERT(g.HoveredWindow == NULL || g.HoveredWindow == g.MovingWindow || g.HoveredWindow->Viewport == g.MousePosViewport);
+    IM_ASSERT(g.HoveredWindow == NULL || g.HoveredWindow == g.MovingWindow || g.HoveredWindow->Viewport == g.MouseRefViewport);
 
     // Modal windows prevents cursor from hovering behind them.
     ImGuiWindow* modal_window = GetFrontMostPopupModal();
@@ -4127,7 +4126,7 @@
     g.FontStack.clear();
     g.OpenPopupStack.clear();
     g.CurrentPopupStack.clear();
-    g.CurrentViewport = g.MousePosViewport = g.MousePosPrevViewport = g.MouseHoveredPrevViewport = NULL;
+    g.CurrentViewport = g.MouseRefViewport = g.MouseRefPrevViewport = g.MouseHoveredLastViewport = NULL;
     for (int i = 0; i < g.Viewports.Size; i++)
         IM_DELETE(g.Viewports[i]);
     g.Viewports.clear();
@@ -4575,7 +4574,7 @@
         for (int viewport_n = 0; viewport_n < g.Viewports.Size; viewport_n++)
         {
             ImGuiViewportP* viewport = g.Viewports[viewport_n];
-            ImVec2 pos = (g.MousePosViewport == viewport) ? main_pos : ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(main_pos, g.MousePosViewport), viewport);
+            ImVec2 pos = (g.MouseRefViewport == viewport) ? main_pos : ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(main_pos, g.MouseRefViewport), viewport);
             if (viewport->GetRect().Overlaps(ImRect(pos, pos + ImVec2(2,2)*sc + size * sc)))
             {
                 ImDrawList* draw_list = GetOverlayDrawList(viewport);
@@ -4674,7 +4673,7 @@
         ImGuiID viewport_id = viewport->ID;
         if (viewport_id == g.IO.MousePosViewport)  // We are early in NewFrame and g.MousePosViewport hasn't been set, patch the source.
             g.IO.MousePos.x += delta_x;
-        if (viewport == g.MousePosPrevViewport)
+        if (viewport == g.MouseRefPrevViewport)
             g.IO.MousePosPrev.x += delta_x;
         for (int mouse_n = 0; mouse_n < IM_ARRAYSIZE(g.MouseClickedPosViewportId); mouse_n++)
             if (g.MouseClickedPosViewportId[mouse_n] == viewport_id)
@@ -5106,7 +5105,7 @@
         if (window->Flags & ImGuiWindowFlags_NoInputs)
             continue;
         IM_ASSERT(window->Viewport);
-        if (window->Viewport != g.MousePosViewport)
+        if (window->Viewport != g.MouseRefViewport)
             continue;
 
         // Using the clipped AABB, a child window will typically be clipped by its parent (not always)
@@ -5134,7 +5133,7 @@
     const ImRect rect_for_touch(rect_clipped.Min - g.Style.TouchExtraPadding, rect_clipped.Max + g.Style.TouchExtraPadding);
     if (!rect_for_touch.Contains(g.IO.MousePos))
         return false;
-    if (!g.MousePosViewport->GetRect().Overlaps(rect_clipped))
+    if (!g.MouseRefViewport->GetRect().Overlaps(rect_clipped))
         return false;
     return true;
 }
@@ -5290,7 +5289,7 @@
         lock_threshold = g.IO.MouseDragThreshold;
     if (g.IO.MouseDown[button])
         if (g.IO.MouseDragMaxDistanceSqr[button] >= lock_threshold * lock_threshold)
-            if (g.MousePosViewport->ID == g.MouseClickedPosViewportId[button])
+            if (g.MouseRefViewport->ID == g.MouseClickedPosViewportId[button])
                 return g.IO.MousePos - g.IO.MouseClickedPos[button];     // Assume we can only get active with left-mouse button (at the moment).
     return ImVec2(0.0f, 0.0f);
 }
@@ -5623,7 +5622,7 @@
     // Center modal windows by default
     // FIXME: Should test for (PosCond & window->SetWindowPosAllowFlags) with the upcoming window.
     if (g.NextWindowData.PosCond == 0)
-        SetNextWindowPos(GetViewportRect(window).GetCenter(), ImGuiCond_Appearing, ImVec2(0.5f, 0.5f));
+        SetNextWindowPos(window->Viewport->GetCenter(), ImGuiCond_Appearing, ImVec2(0.5f, 0.5f));
 
     bool is_open = Begin(name, p_open, flags | ImGuiWindowFlags_Popup | ImGuiWindowFlags_Modal | ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoSavedSettings);
     if (!is_open || (p_open && !*p_open)) // NB: is_open can be 'false' when the popup is completely clipped (e.g. zero size display)
@@ -5848,7 +5847,7 @@
 static ImRect FindScreenRectForWindow(ImGuiWindow* window)
 {
     ImVec2 padding = GImGui->Style.DisplaySafeAreaPadding;
-    ImRect r_screen(ImGui::GetViewportRect(window));
+    ImRect r_screen(window->Viewport->GetRect());
     r_screen.Expand(ImVec2((window->Size.x - r_screen.GetWidth() > padding.x * 2) ? -padding.x : 0.0f, (window->Size.y - r_screen.GetHeight() > padding.y * 2) ? -padding.y : 0.0f));
     return r_screen;
 }
@@ -5927,11 +5926,13 @@
             r_avoid = ImRect(parent_menu->Pos.x + horizontal_overlap, -FLT_MAX, parent_menu->Pos.x + parent_menu->Size.x - horizontal_overlap - parent_menu->ScrollbarSizes.x, FLT_MAX);
         return FindBestWindowPosForPopupEx(window->PosFloat, window->Size, &window->AutoPosLastDirection, r_screen, r_avoid);
     }
+
     if (window->Flags & ImGuiWindowFlags_Popup)
     {
         ImRect r_avoid(window->PosFloat.x - 1, window->PosFloat.y - 1, window->PosFloat.x + 1, window->PosFloat.y + 1);
         return FindBestWindowPosForPopupEx(window->PosFloat, window->Size, &window->AutoPosLastDirection, r_screen, r_avoid);
     }
+
     if (window->Flags & ImGuiWindowFlags_Tooltip)
     {
         // Position tooltip (always follows mouse)
@@ -6060,25 +6061,25 @@
 {
     ImGuiContext& g = *GImGui;
     ImGuiStyle& style = g.Style;
-    ImGuiWindowFlags flags = window->Flags;
-    ImVec2 size_auto_fit;
-    if ((flags & ImGuiWindowFlags_Tooltip) != 0)
+    if (window->Flags & ImGuiWindowFlags_Tooltip)
     {
-        // Tooltip always resize. We keep the spacing symmetric on both axises for aesthetic purpose.
-        size_auto_fit = size_contents;
+        // Tooltip always resize
+        return size_contents;
     }
     else
     {
-        // When the window cannot fit all contents (either because of constraints, either because screen is too small): we are growing the size on the other axis to compensate for expected scrollbar. FIXME: Might turn bigger than ViewportSize-WindowPadding.
-        ImVec2 viewport_size = window->ViewportOwned ? ImVec2(FLT_MAX, FLT_MAX) : window->Viewport->Size;
-        size_auto_fit = ImClamp(size_contents, style.WindowMinSize, ImMax(style.WindowMinSize, viewport_size - g.Style.DisplaySafeAreaPadding));
+        ImVec2 avail_size = window->ViewportOwned ? ImVec2(FLT_MAX, FLT_MAX) : window->Viewport->Size;
+        ImVec2 size_auto_fit = ImClamp(size_contents, style.WindowMinSize, ImMax(style.WindowMinSize, avail_size - g.Style.DisplaySafeAreaPadding));
+
+        // When the window cannot fit all contents (either because of constraints, either because screen is too small),
+        // we are growing the size on the other axis to compensate for expected scrollbar. FIXME: Might turn bigger than ViewportSize-WindowPadding.
         ImVec2 size_auto_fit_after_constraint = CalcSizeAfterConstraint(window, size_auto_fit);
-        if (size_auto_fit_after_constraint.x < size_contents.x && !(flags & ImGuiWindowFlags_NoScrollbar) && (flags & ImGuiWindowFlags_HorizontalScrollbar))
+        if (size_auto_fit_after_constraint.x < size_contents.x && !(window->Flags & ImGuiWindowFlags_NoScrollbar) && (window->Flags & ImGuiWindowFlags_HorizontalScrollbar))
             size_auto_fit.y += style.ScrollbarSize;
-        if (size_auto_fit_after_constraint.y < size_contents.y && !(flags & ImGuiWindowFlags_NoScrollbar))
+        if (size_auto_fit_after_constraint.y < size_contents.y && !(window->Flags & ImGuiWindowFlags_NoScrollbar))
             size_auto_fit.x += style.ScrollbarSize;
+        return size_auto_fit;
     }
-    return size_auto_fit;
 }
 
 static float GetScrollMaxX(ImGuiWindow* window)
@@ -6201,6 +6202,7 @@
     }
     else if (flags & ImGuiWindowFlags_ChildWindow)
     {
+        // Inherit viewport from parent window
         window->Viewport = window->ParentWindow->Viewport;
     }
     else if (window_follow_mouse_viewport && IsMousePosValid())
@@ -6211,7 +6213,7 @@
         if (!window_is_mouse_tooltip && (current_viewport == NULL || !current_viewport->GetRect().Contains(window->Rect())))
         {
             // Calculate mouse position in OS/platform coordinates, create a Viewport at this position.
-            ImVec2 platform_pos = ConvertViewportPosToPlatformPos(g.IO.MousePos - g.ActiveIdClickOffset, g.MousePosViewport);
+            ImVec2 platform_pos = ConvertViewportPosToPlatformPos(g.IO.MousePos - g.ActiveIdClickOffset, g.MouseRefViewport);
             ImGuiViewportFlags viewport_flags = ImGuiViewportFlags_NoDecoration | ImGuiViewportFlags_NoFocusOnAppearing | ImGuiViewportFlags_NoInputs;
             ImGuiViewportP* viewport = AddUpdateViewport(window, window->ID, viewport_flags, platform_pos, window->Size);
             window->Viewport = viewport;
@@ -6219,7 +6221,7 @@
         }
         else
         {
-            window->Viewport = g.MousePosViewport;
+            window->Viewport = g.MouseRefViewport;
         }
     }
     else if (g.NavWindow != NULL && g.NavWindow != window && (flags & ImGuiWindowFlags_Tooltip))
@@ -6231,7 +6233,7 @@
     if (window->Viewport == NULL)
         window->Viewport = main_viewport;
 
-    // When we own the viewport update its size
+    // When we own the viewport update its size/position
     if (window == window->Viewport->Window && !created_viewport)
     {
         window->Viewport->Flags |= ImGuiViewportFlags_NoDecoration;
@@ -6671,7 +6673,7 @@
 
         // Clamp position so window stays visible within its viewport
         // Ignore zero-sized display explicitly to avoid losing positions if a window manager reports zero-sized window when initializing or minimizing.
-        ImRect viewport_rect(GetViewportRect(window));
+        ImRect viewport_rect = window->Viewport->GetRect();
         if (!window_pos_set_by_api && !(flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_Tooltip)) && !window->ViewportOwned && window->AutoFitFramesX <= 0 && window->AutoFitFramesY <= 0)
             if (viewport_rect.GetWidth() > 0 && viewport_rect.GetHeight() > 0.0f)
             {
@@ -6727,7 +6729,7 @@
         if (window->ViewportOwned && (window->Size.x != window->Viewport->Size.x || window->Size.y != window->Viewport->Size.y))
         {
             window->Viewport->Size = window->SizeFull;
-            viewport_rect = GetViewportRect(window);
+            viewport_rect = window->Viewport->GetRect();
         }
 
         // DRAWING
diff --git a/imgui_internal.h b/imgui_internal.h
index e714176..278648d 100644
--- a/imgui_internal.h
+++ b/imgui_internal.h
@@ -529,6 +529,7 @@
     ImGuiViewportP()         { Idx = 1; LastFrameActive = LastFrameAsRefViewport = LastFrameOverlayDrawList = -1; LastNameHash = 0; Alpha = LastAlpha = 1.0f; Window = NULL; OverlayDrawList = NULL; RendererLastSize = ImVec2(-1.0f,-1.0f); }
     ~ImGuiViewportP()        { if (OverlayDrawList) IM_DELETE(OverlayDrawList); }
     ImRect  GetRect() const  { return ImRect(Pos.x, Pos.y, Pos.x + Size.x, Pos.y + Size.y); }
+    ImVec2  GetCenter() const{ return ImVec2(Pos.x + Size.x * 0.5f, Pos.y + Size.y * 0.5f); }
     float   GetNextX() const { const float SPACING = 4.0f; return Pos.x + Size.x + SPACING; }
 };
 
@@ -638,11 +639,11 @@
     ImGuiCond               NextTreeNodeOpenCond;
 
     // Viewports
-    ImVector<ImGuiViewportP*> Viewports;
+    ImVector<ImGuiViewportP*> Viewports;                        // Active viewports (always 1+, and generally 1 unless multi-viewports are enabled). Each viewports hold their copy of ImDrawData. 
     ImGuiViewportP*         CurrentViewport;                    // We track changes of viewport (happening in Begin) so we can call Platform_OnChangedViewport()
-    ImGuiViewportP*         MousePosViewport;
-    ImGuiViewportP*         MousePosPrevViewport;
-    ImGuiViewportP*         MouseHoveredPrevViewport;
+    ImGuiViewportP*         MouseRefViewport;
+    ImGuiViewportP*         MouseRefPrevViewport;
+    ImGuiViewportP*         MouseHoveredLastViewport;           // Last viewport that was hovered by mouse (even if we are not hovering any viewport any more)
     ImGuiID                 MouseClickedPosViewportId[5];       // For rarely used fields we only compare to, store viewport ID only so we don't have to clean dangling pointers
 
     // Navigation data (for gamepad/keyboard)
@@ -728,13 +729,13 @@
     int                     LogAutoExpandMaxDepth;
 
     // Misc
-    float                   FramerateSecPerFrame[120];          // calculate estimate of framerate for user
+    float                   FramerateSecPerFrame[120];          // Calculate estimate of framerate for user over the last 2 seconds.
     int                     FramerateSecPerFrameIdx;
     float                   FramerateSecPerFrameAccum;
-    int                     WantCaptureMouseNextFrame;          // explicit capture via CaptureInputs() sets those flags
+    int                     WantCaptureMouseNextFrame;          // Explicit capture via CaptureKeyboardFromApp()/CaptureMouseFromApp() sets those flags
     int                     WantCaptureKeyboardNextFrame;
     int                     WantTextInputNextFrame;
-    char                    TempBuffer[1024*3+1];               // temporary text buffer
+    char                    TempBuffer[1024*3+1];               // Temporary text buffer
 
     ImGuiContext(ImFontAtlas* shared_font_atlas)
     {
@@ -770,8 +771,8 @@
         NextTreeNodeOpenCond = 0;
 
         CurrentViewport = NULL;
-        MousePosViewport = NULL;
-        MousePosPrevViewport = MouseHoveredPrevViewport = NULL;
+        MouseRefViewport = NULL;
+        MouseRefPrevViewport = MouseHoveredLastViewport = NULL;
         memset(MouseClickedPosViewportId, 0, sizeof(MouseClickedPosViewportId));
 
         NavWindow = NULL;