Viewports: Fix to avoid SetNextWindowViewport being overrided by creation of a standalone viewport. (#2544, #1542)

imgui.cpp

@@ -10552,11 +10552,13 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
         }
     }
 
+    bool lock_viewport = false;
     if (g.NextWindowData.ViewportCond)
     {
         // Code explicitly request a viewport
         window->Viewport = (ImGuiViewportP*)FindViewportByID(g.NextWindowData.ViewportId);
         window->ViewportId = g.NextWindowData.ViewportId; // Store ID even if Viewport isn't resolved yet.
+        lock_viewport = true;
     }
     else if ((flags & ImGuiWindowFlags_ChildWindow) || (flags & ImGuiWindowFlags_ChildMenu))
     {
@@ -10590,6 +10592,8 @@ 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
+    if (!lock_viewport)
+    {
         if (flags & (ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup))
         {
             // We need to take account of the possibility that mouse may become invalid.
@@ -10620,10 +10624,13 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
                 window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_NoFocusOnAppearing);
             }
         }
+        else 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
     window->ViewportOwned = (window == window->Viewport->Window);