GLFW seems to have a problem with fullscreen modes if one screen is set on top of another (working in X11 with XRandr).
I normally set up my screens like this: 'xrandr --output DVI-I-1 --auto --pos 0x0 --primary --output DVI-D-0 --below DVI-I-1 --output HDMI-0 --auto --pos 100x100'
The reason I'm superimposing my screens is because I'm doing software development for the Oculus Rift. It's viewed by the system as a monitor, but you can't really see normal desktop stuff through it very well, so having the output for it overlaid on one of my other monitors is usually helpful.
Here's how it looks when I create a GLFW window using this code
window = glfwCreateWindow(w, h, "glfw", NULL, NULL);
I see this:
But when I try to do full screen with this code
GLFWmonitor * target = ...;
window = glfwCreateWindow(w, h, "glfw", target, NULL);
The Rift display is still showing the same window of the top screen, meaning I see something approximately like this:
When I don't do superimposition, but instead set the Rift outside the areas covered by the existing monitors, then I don't have a problem, and the Rift display looks correct. I'd rather not have to use xrandr to reset the screen layouts every time I want to test something for fullscreen.
Please see GitHub for further discussion.