Monitoring a displays state in python?
python, winapi
Solution
It seems that, when Windows wants to start the screen saver or turn the monitor off, it will send a `WM_SYSCOMMAND` to the topmost window with a `wParam` of `SC_SCREENSAVE` (to start the screen saver) or a `wParam` of `SC_MONITORPOWER` and a `lParam` of 1 or 2 (to turn the monitor off). This message will then be passed to `DefWindowProc`, which will actually do the action. So, if your window happens to be the topmost one, you can intercept these events and ignore them (or do anything else you want before passing them to `DefWindowProc`).
On Windows Vista, there seems to be a more intuitive, and more reliable, way to know the monitor power state. You call `RegisterPowerSettingNotification` to tell the system to send your window a `WM_POWERBROADCAST` message with a `wParam` of `PBT_POWERSETTINGCHANGE` and a `lParam` pointing to a `POWERBROADCAST_SETTING` structure.
I cannot test either of them since I currently do not have any computer with Windows nearby. I hope, however, they point you in the right direction.
References:
- The Old New Thing : Fumbling around in the dark and stumbling across the wrong solution
- Recursive hook ... - borland.public.delphi.nativeapi.win32 | Google Groups
- Registering for Power Events (Windows)
Problem
How can I tell when Windows is changing a monitors power state?