Is the X11 engine slower than raster just because of the drivers?

Here was i profiling KSquares and discovered that when painting an antialiased dashed line using the Qt X11 engine you hit a code path in which Qt tries to detect for each dash of the line which other dashes intersect with it, that's right a O(n^2) calculation that makes no sense, that since you are drawing a line the intersections it will find it's that a dash only intersects with itself. So seeing things like that i wonder if the Raster engine is faster because X11 drivers suck we have been told or it's that the X11 engine code is not as good as it could be. I've checked and the raster engine has no such "bad" loop