Is Screensaver running? Is monitor off?

[TiredOldMan]

I have a program (just a personal project) that watches for a few things and gives me an audio alert in certain cases. 

When I leave the computer, I have it set to run a screensaver after 15 minutes, and then to turn off the monitor after that.  (Not sleep mode, just the power settings "turn off the display" that makes it black.)

It tends to run all the time, but of course, I go to sleep.  And often notice it in the middle of the night, from the other room.

Is there a way I can tell, using Lazarus code, whether the monitor has been shut off?  Whether the screensaver is running?

[balazsszekely]

Hi TiredOldMan,

Welcome to the forum!

Is there a way I can tell, using Lazarus code, whether the monitor has been shut off?  Whether the screensaver is running?

Unfortunately there is no reliable way to tell if the monitor is off or the screensaver is running. The issue is not related to Lazarus, Microsoft does not provide a clear API.
However you can try the following:

1. Detect screensaver status
   a. Create a new project
   b. Add a memo to your form
   c. Add a FormCreate event

Code: Pascal  [Select][+][-]

1. uses jwawindows;
2.  
3. var
4.   PrevWndProc: WNDPROC;
5.  
6. function WndCallback(AHWND: HWND; uMsg: UINT; wParam: WParam; lParam: LParam): LRESULT; stdcall;
7. begin
8.   if uMsg = WM_SYSCOMMAND then
9.   begin
10.     case wParam of
11.       SC_SCREENSAVE:
12.            begin
13.              Form1.Memo1.Lines.Add('Screen saver started');
14.              //make sure you don't block the hook chain with a blocking function like showmessage
15.            end;
16.     end;
17.   end;
18.   Result := CallWindowProc(PrevWndProc, Ahwnd, uMsg, WParam, LParam);
19. end;
20.  
21. procedure TForm1.FormCreate(Sender: TObject);
22. begin
23.   PrevWndProc := jwawindows.WNDPROC(SetWindowLongPtr(Self.Handle, GWL_WNDPROC, PtrUInt(@WndCallback)));
24. end;

1. Detect monitor On/Off
   a. Create a new project
   b. Add a memo to your form
   c. Add a timer to your form, create an OnTimer event
   c. Add a FormCreate event

Code: Pascal  [Select][+][-]

1. uses jwawindows;
2.  
3. type
4.   TMonitorState = (msUnknown, msOff, msOn);
5.  
6. var
7.   MonitorState: TMonitorState;
8.  
9. function CheckMonitorState: TMonitorState;
10. var
11.   P: Point;
12.   Monitor: HMONITOR;
13.   Res: BOOL;
14. begin
15.   Result := msUnknown;
16.   P.X := 0;
17.   P.Y := 0;
18.   Monitor := MonitorFromPoint(P, MONITOR_DEFAULTTOPRIMARY);
19.   if Monitor <> NULL then
20.   begin
21.     Res := False;
22.     if GetDevicePowerState(Monitor, Res) then
23.     begin
24.       case Res of
25.         False: Result := msOff;
26.         True: Result := msOn;
27.       end;
28.     end;
29.   end;
30. end;
31.  
32. procedure TForm1.FormCreate(Sender: TObject);
33. begin
34.   MonitorState := CheckMonitorState;
35. end;
36.  
37. procedure TForm1.Timer1Timer(Sender: TObject);
38. var
39.   Temp_MonitorState: TMonitorState;
40. begin
41.   Temp_MonitorState := CheckMonitorState;
42.   if MonitorState <> Temp_MonitorState then
43.   begin
44.     Temp_MonitorState := MonitorState;
45.     case MonitorState of
46.       msUnknown: Memo1.Lines.Add('Monitor state unknown');
47.       msOff: Memo1.Lines.Add('Monitor state off');
48.       msOn: Memo1.Lines.Add('Monitor state on');
49.     end;
50.   end;
51. end;

For me the screensaver status detection works fine, the monitor state doesn't. The later depends on your hardware.

[ASerge]

However you can try the following:

A few remarks:
1. For the WM_SYSCOMMAND message, wParam must be masked with $FFF0. Source WM_SYSCOMMAND.
2. SetWindowLongPtr is a very old message interception technique. Starting with XP, windows subclassing is used.
3. From GetDevicePowerState "This function cannot be used to query the power state of a display device". In most cases, this is not the true, but for some manufacturers it is true (depends on the device driver).
This is my example:

Code: Pascal  [Select][+][-]

1. uses Windows, CommCtrl;
2.  
3. type
4.   PPOWERBROADCAST_SETTING = ^POWERBROADCAST_SETTING;
5.   POWERBROADCAST_SETTING = record
6.     PowerSetting: GUID;
7.     DataLength: DWORD;
8.     Data: array[0..0] of UCHAR;
9.   end;
10.  
11. const
12.   GUID_CONSOLE_DISPLAY_STATE: TGuid = '{6FE69556-704A-47A0-8F24-C28D936FDA47}';
13.   GUID_MONITOR_POWER_ON: TGuid = '{02731015-4510-4526-99E6-E5A17EBD1AEA}';
14.   CSomeSubclassId = 1;
15.  
16. function NewWndProc(Wnd: HWND; uMsg: UINT; wParam: WPARAM; lParam: LPARAM; uISubClass: UINT_PTR; dwRefData: DWORD_PTR): LRESULT; stdcall;
17. var
18.   Form: TForm1 absolute dwRefData;
19.  
20.   procedure LogEvent(const Event: string);
21.   begin
22.     Form.Memo1.Append(Event + ' at ' + DateTimeToStr(Now));
23.   end;
24.  
25. const
26.   WM_POWERBROADCAST = 536;
27.   PBT_POWERSETTINGCHANGE = 32787;
28. var
29.   Event: PPOWERBROADCAST_SETTING absolute lParam;
30. begin
31.   case uMsg of
32.     WM_SYSCOMMAND:
33.       if wParam and $FFF0 = SC_SCREENSAVE then
34.         LogEvent('Screen saver started');
35.     WM_POWERBROADCAST:
36.       if (wParam = PBT_POWERSETTINGCHANGE)
37.         and (IsEqualGUID(Event^.PowerSetting, GUID_CONSOLE_DISPLAY_STATE)
38.           or IsEqualGUID(Event^.PowerSetting, GUID_MONITOR_POWER_ON)) then
39.         begin
40.           case Event^.Data[0] of
41.             0:
42.               LogEvent('The monitor is off');
43.             1:
44.               LogEvent('The monitor is on');
45.             2:
46.               LogEvent('The monitor is dimmed');
47.           end;
48.         end;
49.   end;
50.   Result := DefSubclassProc(Wnd, uMsg, wParam, lParam);
51. end;
52.  
53. procedure TForm1.Button1Click(Sender: TObject);
54. begin
55.   RegisterPowerHook;
56. end;
57.  
58. procedure TForm1.Button2Click(Sender: TObject);
59. begin
60.   UnregisterPowerHook;
61. end;
62.  
63. procedure TForm1.FormDestroy(Sender: TObject);
64. begin
65.   UnregisterPowerHook;
66. end;
67.  
68. function RegisterPowerSettingNotification(hRecipient: THandle; PowerSettingGuid: PGuid; Flags: DWORD): Pointer; stdcall; external User32;
69.  
70. function UnregisterPowerSettingNotification(Handle: Pointer): BOOL; stdcall; external User32;
71.  
72. procedure TForm1.RegisterPowerHook;
73. const
74.   DEVICE_NOTIFY_WINDOW_HANDLE = 0;
75. begin
76.   if not Assigned(PNewRegStateInfo) then
77.     PNewRegStateInfo := RegisterPowerSettingNotification(Handle, @GUID_CONSOLE_DISPLAY_STATE, DEVICE_NOTIFY_WINDOW_HANDLE);
78.   if not Assigned(PNewRegStateInfo) then // check PNewRegStateInfo not POldRegStateInfo
79.     POldRegStateInfo := RegisterPowerSettingNotification(Handle, @GUID_MONITOR_POWER_ON, DEVICE_NOTIFY_WINDOW_HANDLE);
80.   SetWindowSubclass(Handle, @NewWndProc, CSomeSubclassId, DWORD_PTR(Self));
81. end;
82.  
83. procedure TForm1.UnregisterPowerHook;
84. begin
85.   RemoveWindowSubclass(Handle, @NewWndProc, CSomeSubclassId);
86.   if Assigned(PNewRegStateInfo) then
87.   begin
88.     UnregisterPowerSettingNotification(PNewRegStateInfo);
89.     PNewRegStateInfo := nil;
90.   end;
91.   if Assigned(POldRegStateInfo) then
92.   begin
93.     UnregisterPowerSettingNotification(POldRegStateInfo);
94.     POldRegStateInfo := nil;
95.   end;
96. end;

[balazsszekely]

@ASerge
Thanks! Cool stuff. I will run a few tests tomorrow and report back.

[TiredOldMan]

Haven't had a chance to play with this yet, but I did want to say thanks for the responses.

[balazsszekely]

@ASerge
I had to wrestle with SetWindowSubclass, RemoveWindowSubclass, DefSubclassProc APIs. Anyways the project compiles fine now, however the monitor off is still not detected at my side. Does it work for you?

@TiredOldMan

Haven't had a chance to play with this yet, but I did want to say thanks for the responses

Please test attached project.

[ASerge]

@ASerge
Anyways the project compiles fine now, however the monitor off is still not detected at my side. Does it work for you?

It works for me.