Hi,

I'm trying to setup a triplemonitor setup on two graphic cards. As hardware I've an 9500 GT and a GeForce 210. I've connected two identical monitors to the 9500 GT which I use as my primary screens and another, with secondary usage, to the 210. I don't care very much about what's on the third monitor. If KDE doesn't run on it at all that's fine, as long as I can start a Konsole or xterm on it. I also don't need to drag windows to or from it, but I want to be able to drag windows between my two primary screens. I also want to have windows maximizing on one of my primary screens. It works flawlessy in Windows, so the hardware is fine. I run Debian testing, KDE 4.6.

I've tried a lot of things, but it doesn't work:

• Three separate X screens. Without Xinerama I can't drag windows between the primary two screens, and with Xinerama it's really slow (that's a known problem in the nvidia driver)
• One big X screen. This doesn't work as I've two graphic cards.
• One X screen with TwinView for the primary displays and a second one for the secondary display. This works fine, except that maximizing windows maximizes them over the two screens, not on one. Plasma also keeps projecting a workspace for the third screen on the top-left of the first screen. Enabling or disabling Xinerama doesn't help. With a fake xinerama solution (an LD_PRELOAD library with hardcoded Xinerama info) it doesn't work either.

Does anybody have an idea how I can get this working with KDE? I'm willing to try anything (I've quite some development experience so I can also try out patches to KDE etc).

4.7 has some fixes with regards to multiscreen support (and a few more are queued for 4.. Ultimately, however, a lot of problems stem from the fact that NVIDIA does not support the X Resize and Rotate (XRandR) extension (but they may eventually, according to recent news). IIRC even the (sub optimal) binary blob from ATI has some kind of support.

Hmm, I've tried 4.7 now but that doesn't work either. However, I've some more details on what works and what doesn't:

• A setup with three separate X screens and Xinerama is slow (a bug in the nvidia driver they won't fix)
• A setup with three separate X screens and without Xinerama works fine, but I can't drag windows across my screens
• A setup with two X screens (one for each graphic card, using twinview to join the two monitors on one graphic card) works fine, but KDE sees all monitors on one graphic card as a single monitor, which causes problems when maximizing.

Is there any way I can manually enter the display geometry instead of letting KDE autodetect them? I've had this working with OpenBox and a fakexinerama (a preloaded library that overrules the calls to Xinerama functions that return data about display geometry and replace them with static data) solution, but that doesn't work with KDE. Does KDE use any other way to gather data about screen geometry?

IIRC KDE uses XRandR first, then other fallbacks in Qt to query screen geometry.