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OpenGL DualMonitors ?

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Just wondering how you would add support for dualmonitor display with opengl. I don't have a second monitor, so I cant try it, just would like to find some resources to get started and then test it somewhere else. I have googled quite a bit, but couldn't find anything. could it be that you just size the window-width to the double size of the screen ? Or do you have to use multiple windows and move the second window to the center of both monitors ? Question goes for Win32, Linux, MacOsX.

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It is a very platform specific topic, I am afraid, although some high-end windowing toolkits provide support for it. Look around for windowing solutions which also target Virtual Reality applications, and you should have some luck.

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Create one OpenGL window/context/whatever for each monitor =P It's as simple as that, although it can lead to headaches if you have to adapt code that was originally made for a single monitor (normally it's just a matter of setting what context to render next, but you never know what stupid quirk the code may have...).

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You might run into a problem too...

In all the dual monitor setups I've seen, only one monitor had hardware accelerated graphics.

IE if you had a windowed game running, you'd get a lot higher FPS on one monitor vs the other.

Just somethin to be aware of!

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It also depends how the user has configured their dual monitors.

Most often it's set up as "dual view", where they are two independent displays. However, the user may have configured them to act as a single (Large) monitor with a weird resolution, in which case you just have to support this large-resolution and know where the split occurs.
I've worked on a system that used this mode in the past, and found that only one half of the large virtual-screen (i.e. one physical screen) would use quality-enhancements such as AA or Aniso-filtering...

To get around the "only one monitor is HW accelerated" problem mentioned above, you can render the slow screen's content to a texture using the accelerated context. The slow context then just has to blit this texture to the screen.

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All dual monitor setups I've seen so far (and including mine) had a) hardware acceleration for all screens and b) consisted of a single desktop area that was not rectangular (eg. 1600x1200 with the right border leading into a 1920x1080 screen). Does anyone really use it as mirrored or separate screens?

Supreme Commander supports this nicely, you have two fully functional game screens, usually I leave the left one zoomed out to act as an overhead map and use the right one to play. Or zoom the left one to my army and the right one to the place I want to arrange them at, so I don't need to scroll to select the different units.

It's a D3D game, though. In Direct3D, a dual-head graphics card with two monitors attached simply appears as two Direct3D devices with different supported resolutions. I guess it's similar in OpenGL, you'd just create two windows and two contexts.

The only problem is if you move a 3D rendering window between the two screens. The application needs to detect this and recreate another D3D device / OGL context for the other screen. And if the window is placed in the middle between two screens, you either have to do a slow memory copy (that's what XNA does) or keep two devices/contexts around.

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Original post by Cygon
All dual monitor setups I've seen so far (and including mine) had a) hardware acceleration for all screens and b) consisted of a single desktop area that was not rectangular (eg. 1600x1200 with the right border leading into a 1920x1080 screen). Does anyone really use it as mirrored or separate screens?
What you just described is two separate screens. The "single virtual screen" setting would show up as a single device, e.g. 3200x1200.
Also, in the case I mentioned, both screens were accelerated, but one still took shortcuts (ignoring quality hints/preferences).

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