I occasionally write utilities for my computer that make my life a bit easier. This morning I was looking for a way to detect whether the monitor was turned off on my Linux laptop. The best advice I came across was using xset -q and parsing the following section:
DPMS (Energy Star):
Standby: 0 Suspend: 0 Off: 0
DPMS is Enabled
Monitor is On
Wait, what? After diving into some C code, it turns out that this can be very simply done with a bit of dotnet core code:
namespace Laptop {
class Display {
[DllImport("libX11")]
private static extern IntPtr XOpenDisplay(string displayName);
[DllImport("libX11")]
private static extern void XCloseDisplay(IntPtr display);
[DllImport("libXext.so.6")]
private static extern bool DPMSQueryExtension(IntPtr display, out string dummy1, out string dummy2);
[DllImport("libXext.so.6")]
private static extern bool DPMSCapable(IntPtr display);
[DllImport("libXext.so.6")]
private static extern void DPMSInfo(IntPtr display, out State state, out bool onOff);
public State IsOn(string displayAddress = ":0")
{
// get a handle to the display, but don't forget to close it!
var display = XOpenDisplay(displayAddress);
if (display == IntPtr.Zero)
{
return State.Fail; // return
}
var reading = State.Fail;
// attempt to read the state from the display
if (DPMSQueryExtension(display, out var dummy1, out var dummy2))
if (DPMSCapable(display))
{
DPMSInfo(display, out var state, out var onOff);
if (onOff) reading = state;
}
// close our handle to the display
XCloseDisplay(display);
return reading;
}
public enum State
{
Fail = -1,
On = 0,
Standby = 1,
Suspend = 2,
Off = 3,
}
}
}
And bam, we can get the display state with Display.IsOn().