When the claws-mail window has to redraw itself because I switch to the desktop it was on, it takes quite some time to do so. It is even slower than firefox. :(
works for me. if this is always reproducible for you then explain more, please
I had similar issue and tracked it down to 2 factors: (1) Upgrade to kernel >= 3.0 slowed down, it's as fast as usual with linux 2.6.39 (2) Gnome-settings-daemon doing the GTK theming. It was slow even with default theme 'advaita'. No OpenGL eye candy enabled here. Disabling gsd accelerated a lot too. But only the kernel downgrade achieved the 'usual' speed. This is amd64 with nvidia GeForce7300 and maybe finally the Xorg nvidia driver is to blame. But comparing many other machines with linux i know, it is my belief that GTK generally is slow as hell, in nearly any other GTK application. Firefox is doing quite some optimization, it seems, to continue to be fast.
kernel 3.0, nvidia GeForce 6150SE, kde here. everything fine.
Ups, forgot to add my comment in the bug tracker. I don't think it is the kernel you should blame the blame is on Gnome3. I have a similar setup kernel (3.0 and 3.1) and I see no slow GTK. The difference is that I use XFCE-4.8 and I have disabled start of Gnome and KDE services in "Sessions and Startup". It could be interesting to know whether the same experience applies to your computer? PS. no Nvidia here. On-board Intel graphics driver.
I had the same problem some months ago. When switching to the desktop where Claws was running, the background clears, Claws thinks for 1 to 2 seconds, then redraws. I'm using no compositor, just a simple Windowmanager (IceWM), no Gnome, no KDE. As it was _very_ annoying, I tried to figure out was causing the delay. First, during the delay, the CPU was at 100%. Then, it happened with all Gtk2 applications (and only with them). Gtk1, Qt, etc was OK. Before I could really figure out what was causing the delay (I was presuming that some cached data was discarded when the window was unmapped, maybe glyph outlines), there was an update of the graphics driver (radeon r600, maybe it was the switch from r600 to r600g on Debian Wheezie) and the problem vanished. So, check whether it happens with other Gtk2 apps, too and if that's the case, bring it to the Gtk team. Somehow they are using something, that's not always hw-accelerated and is very slow in the software-fallback. The modern graphics drivers are sometimes very strange - they can be extremely fast but may fail completely on trivial stuff (such as line widths != 0. I have a no-toolkit app using only XDrawLine and XCopyArea that redraws faster on a 15 years old PC with a 4MB PCI graphics card than on my modern dual-core r600 system!)