The algorithm for painting characters derives from freetype, not Xft, which is X-server level font handling and makes no assumptions about the actual details of antialiasing of specific font types (in old X, fonts were displayed as on or off pixels, period - no shading possible). Qt interfaces directly to Xft, while GTK has a separate layer, Pango, for font handling. Because they both end up running through freetype via Xft, they both make nice looking fonts, but the use of it in Qt is thoroughgoing and properly low level, while typically GTK has a zillion complex interrelated APIs, like Windows, because it just seems to grow according to demand and not according to design, also like Windows.