Comment 32 for bug 830949

NB: While enabling the copy to texture plugin on the compiz side of things will allow compiz to work correctly on its own, unity and nux do not have code to handle splitting up textures and drawing them individually, ensuring that they do not exceed GL_MAX_TEXTURE_SIZE .

This means that you'll be able to run compiz on its own, but it is likely that drawing past any dimention which is larger than the maximum texture size that unity does will fail. This means that full-screen effects such as full-screen blur will not work correctly. There isn't code in unity in place at the moment to disable such effects in this case - please use CompizConfig Settings Manager to disable the Dash blur before testing monitor add / remove.

That being said, all of unity's widgets are done per-monitor, and unless the actual monitor dimentions are larger than GL_MAX_TEXTURE_SIZE itself, then it isn't likely that this limit will be hit.

You can query the maximum texture size by doing

glxinfo -l | grep GL_MAX_TEXTURE_SIZE

Which will return a single value for how large the screen space can be in any one direction. Any window that draws a desktop window shared over both monitors (I believe nautilus does this) will request a backing pixmap that large. Else - you can test this by resizing a window to be so large that it exceeds that size (check the dimentions with xwininfo)