Discovered when working on bug 3753. Modern QT applications are not using XCopyArea. Instead, they are using a backing store pixmap and redrawing everything every time. This means that we cannot use VNC CopyRect updates. From http://labs.qt.nokia.com/2008/10/22/so-long-and-thanks-for-the-blit/: “But hey, this means we have tons of XPutImage calls as part of the repainting, doesn’t it?” you are probably thinking. Luckily not… The raster graphics system is using the X Shared Memory extension to allocate the bits shared with an XPixmap so the end of a paint is a mere XCopyArea, which happens in-place on the X server, so it is quite cheap. Needless to say this is a solution that works best on local displays, but that does cover most of the Linux desktops out there, so it should be a gain in general." Although it's possible to change the graphics system, it is unclear if you can get the old behaviour.
