fix: don't use DPI aware functions on Qt 5 (Windows 7/8) (#5391)

CHANGELOG.md

@@ -3,7 +3,7 @@
 ## Unversioned
 
 - Major: Release plugins alpha. (#5288)
-- Major: Improve high-DPI support on Windows. (#4868)
+- Major: Improve high-DPI support on Windows. (#4868, #5391)
 - Minor: Add option to customise Moderation buttons with images. (#5369)
 - Minor: Colored usernames now update on the fly when changing the "Color @usernames" setting. (#5300)
 - Bugfix: If a network request errors with 200 OK, Qt's error code is now reported instead of the HTTP status. (#5378)

src/widgets/BaseWindow.cpp

@@ -121,12 +121,19 @@ RECT windowBordersFor(HWND hwnd, bool isMaximized)
     auto addBorders = isMaximized || isWindows11OrGreater();
     if (addBorders)
     {
+        // GetDpiForWindow and GetSystemMetricsForDpi are only supported on
+        // Windows 10 and later. Qt 6 requires Windows 10.
+#    if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
         auto dpi = GetDpiForWindow(hwnd);
+#    endif
+
         auto systemMetric = [&](auto index) {
+#    if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
             if (dpi != 0)
             {
                 return GetSystemMetricsForDpi(index, dpi);
             }
+#    endif
             return GetSystemMetrics(index);
         };