Viewports: Fixed being unable to refocus windows when ConfigViewportsNoTaskBarIcon + ConfigViewportsNoDecoration are enabled. (#2420, #1542) [@PathogenDavid] + comments.

imgui.cpp

@@ -5611,13 +5611,19 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
 
             // Update common viewport flags
             ImGuiViewportFlags viewport_flags = (window->Viewport->Flags) & ~(ImGuiViewportFlags_TopMost | ImGuiViewportFlags_NoTaskBarIcon | ImGuiViewportFlags_NoDecoration);
+            const bool is_short_lived_floating_window = (flags & (ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup)) != 0;
             if (flags & ImGuiWindowFlags_Tooltip)
                 viewport_flags |= ImGuiViewportFlags_TopMost;
-            if (g.IO.ConfigViewportsNoTaskBarIcon || (flags & (ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup)) != 0)
+            if (g.IO.ConfigViewportsNoTaskBarIcon || is_short_lived_floating_window)
                 viewport_flags |= ImGuiViewportFlags_NoTaskBarIcon;
-            if (g.IO.ConfigViewportsNoDecoration || (flags & (ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup)) != 0)
+            if (g.IO.ConfigViewportsNoDecoration || is_short_lived_floating_window)
                 viewport_flags |= ImGuiViewportFlags_NoDecoration;
-            if ((viewport_flags & ImGuiViewportFlags_NoDecoration) && (viewport_flags & ImGuiViewportFlags_NoTaskBarIcon))
+
+            // For popups and menus that may be protruding out of their parent viewport, we enable _NoFocusOnClick so that clicking on them
+            // won't steal the OS focus away from their parent window (which may be reflected in OS the title bar decoration).
+            // Setting _NoFocusOnClick would technically prevent us from bringing back to front in case they are being covered by an OS window from a different app, 
+            // but it shouldn't be much of a problem considering those are already popups that are closed when clicking elsewhere.
+            if (is_short_lived_floating_window)
                 viewport_flags |= ImGuiViewportFlags_NoFocusOnAppearing | ImGuiViewportFlags_NoFocusOnClick;
 
             // We can overwrite viewport flags using ImGuiWindowClass (advanced users)