Viewport: Fixes moving child menu viewport (fix 379733a).

imgui.cpp

@@ -7728,14 +7728,17 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
         window->Viewport = main_viewport;
 
     // Mark window as allowed to protrude outside of its viewport and into the current monitor
-    // We need to take account of the possibility that mouse may become invalid.
     if (flags & (ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup))
     {
+        // We need to take account of the possibility that mouse may become invalid.
+        // Popups/Tooltip always set ViewportAllowPlatformMonitorExtend so GetWindowAllowedExtentRect() will return full monitor bounds.
         ImVec2 mouse_ref = (flags & ImGuiWindowFlags_Tooltip) ? g.IO.MousePos : g.CurrentPopupStack.back().OpenMousePos;
         bool use_mouse_ref = (g.NavDisableHighlight || !g.NavDisableMouseHover || !g.NavWindow);
         bool mouse_valid = IsMousePosValid(&mouse_ref);
         if ((window->Appearing || (flags & ImGuiWindowFlags_Tooltip)) && (!use_mouse_ref || mouse_valid))
             window->ViewportAllowPlatformMonitorExtend = FindPlatformMonitorForPos((use_mouse_ref && mouse_valid) ? mouse_ref : NavCalcPreferredRefPos());
+        else 
+            window->ViewportAllowPlatformMonitorExtend = window->Viewport->PlatformMonitor;
     }
     else if (window->Viewport && window != window->Viewport->Window && window->Viewport->Window && !(flags & ImGuiWindowFlags_ChildWindow))
     {
@@ -7755,8 +7758,9 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
             window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_NoFocusOnAppearing);
         }
     }
-
-    if (window->ViewportAllowPlatformMonitorExtend < 0 && (flags & ImGuiWindowFlags_ChildWindow) == 0)
+    // 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)
         window->ViewportAllowPlatformMonitorExtend = window->Viewport->PlatformMonitor;
 
     // Update flags