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This is some really interesting stuff by +Alexander Monakov. Works quite nicely when combined with bumblebee - simply "optirun bash" to keep your card active in the proper configuration, then run this in a separate terminal. Not quite ready for mass-consumption yet, but this has the potential of replacing the VirtualGL part of Bumblebee in the future!
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Don't want to sound dumb, but what will this enable me to do?
+David Whyte, from a user perspective, primus, if successful, will let you get better performance and/or less power consumption when using Bumblebee by replacing VirtualGL
And to further clarify in simple terms, Bumblebee uses VirtualGL to copy the image generated by the second (faster) GPU to your display. VirtualGL was intended for use over a network though, so it takes a great many steps to enable this (compression, sending the image over a network link, decompression, etc).

primus doesn't perform all these "extra" steps, instead taking a more direct route (copying the rendered image in memory to the other GPU, then displaying there). In theory this should get you better performance as well as better compatibility. Running applications will "see" the OpenGL implementation of your real hardware, nothing virtual is presented to them. Hope that clears things up a bit more :-)
Any idea when TBP will enable using it then since it should perform a lot nicer.
It's not working fully in most common cases yet... But once it is, an updated release using primus instead of VirtualGL shouldn't be far away. The bumblebee system was designed with the possibility in mind that we might use something other than VirtualGL in the future, so only minor changes are required here.
Thanks for the clarification. I was hoping it was going to help me display my XPS 14z's display on an external display without having to configure another X server etc.

I have no understanding of the inner workings of the display hardware but couldn't something similar be done to copy the images from the internal GPU for output to the second GPU to enable an external display to be used?

(FYI the 14z has display port and HDMI connected to the nVidia GPU)
+David Whyte Yes, you could do that by simply switching the bumblebee xorg.conf files around (have the external be your main display and the internal the secondary). You still need to have two X servers running in that case though, and it doesn't make much sense since the nvidia-powered display will be way faster than the internal one...

PRIME (not primus) does do what you want, basically allowing you to display whatever you want on any output using any GPU to accelerate it.
In the meanwhile, you may want to look into x11vnc - it allows you to VNC into a running X server, and you could use this to VNC into the X server running on the secondary GPU from your first X session, basically duplicating your display. Note that you will have some "lag", but I've tried this myself and it does work nicely for things like presenting etc.
Thanks. Some of these alternatives are new to me, so I will look into them. Cheers :-)
Hi, sorry for hassling you guys. I searched for more info and the x11vnc route seems the most suitable approach at the moment. Is there any good write ups on this method? Is it just a case of starting the nVidia X server and running vncviewer in it to mirror my laptop display?
Hmmm!  So I ran 'optirun nvidia-settings -c :8' from a terminal to start the nvidia card.  I then ran 'DISPLAY=:8.0 vncviewer localhost:0' from a second terminal and I do get my laptop display mirrored on my external display but it isn't really usable for the following reasons:
1) It doesn't stretch to fill the monitor (not a major issue).
2) I can't see the laptop displays mouse from the external display, I just get a 'dot' wwhen the mouse is in the external display's X-server.
3) I am getting duplication of certain key presses, like open and close parenthesis.

I realise this isn't a support forum.  Where can I go to get help with configuring this particular arrangement with bumblebee?  Cheers.
Can the master repo be updated? The projects gives a false impression that is stalled :(
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