View Full Version : 1 RC on Window spanning 2 Monitors

07-08-2010, 01:46 PM
Is it possible to have one OpenGL Rendering context in a window that spans two monitors?
From the small test I was doing it looked like it does not really work. When I render a textured Quad on the whole window, I would expect that the texture is stretched over the whole area spanning both monitors.
What I saw instead looked as if in fact I had two rendering Contexts. The texture was rendered twice - having each Monitor filled with the complete texture.

I am now wondering whether i did something wrong / forgot something or if it conceptually does make sense at all to have one DC and RC spanning two monitors?

07-08-2010, 02:16 PM
What you describe is the default 2 monitors mode on Windows.
With an Nvidia card (I am not familiar with ATI), you can use a so-called "span" mode which lies to Windows, saying it is only one continuous monitor. This way, only one DC is used for a window covering both monitors.

07-08-2010, 02:43 PM
Thanks a lot. I am using an NVIDIA FX3800 card and Windows 7 64bit. In the windows screen resolution settings the monitors are set to "extend desktop to this display". In the NVIDIA control panel i can not see a setting for the "span" mode. Where can I find this setting?

07-08-2010, 04:37 PM
Something like "Set up multiple displays" (roughly back translated from my french version here).
There can be something called nView, TwinView, ...
And you should be able to set to clone mode too.

07-09-2010, 05:37 AM
Span mode is no longer supported since Vista(driver model restriction iirc).

So you can only have multiple monitors via extended desktop.
Still, a OpenGL window might span multiple monitors.

There will be small performance drop when the window spans multiple monitors on one card(i guess the graphics driver has to copy pixel data internally).

07-09-2010, 05:38 AM
Ah, thanks for the correction.

07-14-2010, 01:42 AM
I've run into the same problem.
Im using a GeForce fx 5700LE with Win XP Pro SP3, nVidia calls their multiple monitor spanning setup DualView. From what I have encountered, you cannot use fullscreen mode to span two monitors, but you can use windowed mode. In doing this, you cannot use the nVidia nView button for "Maximize to Desktop"(in my opengl apps this will always kill the window). If you manually stretch the window it usually works. Like Nighthawk mentioned, the result might not be what you expected or even wanted, and any movement or rotation will look jagged.

07-14-2010, 03:59 AM
DualView and Span are opposite, afaik.
Indeed Dualview does not support fullscreen across monitors, But Span does.