Programmatically prevent Windows screensaver from starting

Question

Is there a recommended way to prevent the Windows screensaver from starting? The closest thing I've found is this article, but what I would really like to do is just tell Windows that the computer isn't idle rather than fooling with the currently set screensaver values.

Answer 1

See answer to this question:
http://stackoverflow.com/questions/394227/off-screen-rendering-when-laptop-shuts-screen-down

Answer 2

This blog post details what you need to do in C++.

The actual code snippet from the website:

LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
  switch (uMsg)                  
  {
    case WM_SYSCOMMAND:
    {
      switch (wParam)
      {
        case SC_SCREENSAVE:  
          return 0;
        case SC_MONITORPOWER:
          return 0;      
      }
      break;      
    }

    case WM_CLOSE:                
    {
      PostQuitMessage(0);            
      return 0;        
    }
  }
  return DefWindowProc(hWnd,uMsg,wParam,lParam);

}

Answer 3

> the actual code snippet from the website:

No. The code is a copy from MSDN before Vista and was added on MSDN-Online... for 16 years ! Never read blogs (BS, not professional at all)

Answer 4

Subtle. The official way to tell Windows that the system is not idle is SetThreadExecutionState. This resets the idle timer, (or turns it off, if you pass ES_CONTINUOUS ). However, even though SetThreadExecutionState resets the idle timer, it does not stop the screensaver!

Answer 5

I use Mouse Jiggler to reset the idle state. This gets around a Group Policy that tends to start my screensaver (and lock the machine) at inopportune times: when I'm reading a long document, studying a complex chunk of code, or talking/listening/not-constantly-typing during a meeting.

As it can be slightly annoying to have the mouse jump 1px diagonally every second, I intend to use AutoHotKey to write a script that does basically the same thing, but only after a configured keyboard/mouse idle timeout, and maybe use the Shift key (or Scroll Lock) instead of a mouse move.

Answer 6

SystemParametersInfo

Specifically, the SPI_SETSCREENSAVEACTIVE parameter.

Does this not work? I was surprised that I did not see it here. Note that SetThreadExecutionState will not affect the screen saver at all, just the sleeping of the display.

Answer 7

For testing, I set the screensaver to 1 minute and required a password.

I tried capturing SC_SCREENSAVE and returning -1 in VB .Net. As commented, it works when there is no screensaver password but fails if the screensaver password is active. (I tried it in Windows XP). I also put this into a Timer's tick event, every 1000 milliseconds:

Static dir As Integer = 4
Cursor.Position = Cursor.Position + New Size(dir, dir)
dir = -dir

It doesn't work. The cursor jiggles back and forth and after 1 minute the screensaver flashes on for a short instance and then turns off. The screensaver turns on for only a moment, not long enough to require a password. But still, the flash is ugly.

Then I tried using user32.dll's SetCursorPos and GetCursorPos. You can look them up at pinvoke. Same result as above.

Then I peeked at the code of "JiggleMouse" mentioned elsewhere in this question. JiggleMouse uses SendInput. SendInput works! No flash of the screensaver. I put a call to SendInput inside of a Timer that triggers every 50 seconds (just less than the minimum screensaver timeout of 60 seconds). It's sufficient to move the mouse by a delta of 0,0, no real movement. That does work. The code to put in the Tick event:

Dim i(0) As INPUT
i(0).dwType = INPUT.InputType.INPUT_MOUSE
i(0).mkhi = New MOUSEKEYBDHARDWAREINPUT
i(0).mkhi.mi = New MOUSEINPUT
i(0).mkhi.mi.dx = 0
i(0).mkhi.mi.dy = 0
i(0).mkhi.mi.mouseData = 0
i(0).mkhi.mi.dwFlags = MOUSEINPUT.MouseEventFlags.MOUSEEVENTF_MOVE
i(0).mkhi.mi.time = 0
i(0).mkhi.mi.dwExtraInfo = IntPtr.Zero
SendInput(1, i(0), Marshal.SizeOf(i(0)))

This comes from pinvoke.com:

Public Declare Function SendInput Lib "user32" (ByVal nInputs As Integer, ByRef pInputs As INPUT, ByVal cbSize As Integer) As Integer

Public Structure INPUT
    Enum InputType As Integer
        INPUT_MOUSE = 0
        INPUT_KEYBOARD = 1
        INPUT_HARDWARE = 2
    End Enum

    Dim dwType As InputType
    Dim mkhi As MOUSEKEYBDHARDWAREINPUT
End Structure

Public Structure MOUSEINPUT
    Enum MouseEventFlags As Integer
        MOUSEEVENTF_MOVE = &H1
        MOUSEEVENTF_LEFTDOWN = &H2
        MOUSEEVENTF_LEFTUP = &H4
        MOUSEEVENTF_RIGHTDOWN = &H8
        MOUSEEVENTF_RIGHTUP = &H10
        MOUSEEVENTF_MIDDLEDOWN = &H20
        MOUSEEVENTF_MIDDLEUP = &H40
        MOUSEEVENTF_XDOWN = &H80
        MOUSEEVENTF_XUP = &H100
        MOUSEEVENTF_WHEEL = &H800
        MOUSEEVENTF_VIRTUALDESK = &H4000
        MOUSEEVENTF_ABSOLUTE = &H8000
    End Enum

    Dim dx As Integer
    Dim dy As Integer
    Dim mouseData As Integer
    Dim dwFlags As MouseEventFlags
    Dim time As Integer
    Dim dwExtraInfo As IntPtr
End Structure

Public Structure KEYBDINPUT
    Public wVk As Short
    Public wScan As Short
    Public dwFlags As Integer
    Public time As Integer
    Public dwExtraInfo As IntPtr
End Structure

Public Structure HARDWAREINPUT
    Public uMsg As Integer
    Public wParamL As Short
    Public wParamH As Short
End Structure

Const KEYEVENTF_EXTENDEDKEY As UInt32 = &H1
Const KEYEVENTF_KEYUP As UInt32 = &H2
Const KEYEVENTF_UNICODE As UInt32 = &H4
Const KEYEVENTF_SCANCODE As UInt32 = &H8
Const XBUTTON1 As UInt32 = &H1
Const XBUTTON2 As UInt32 = &H2

<StructLayout(LayoutKind.Explicit)> Public Structure MOUSEKEYBDHARDWAREINPUT
    <FieldOffset(0)> Public mi As MOUSEINPUT
    <FieldOffset(0)> Public ki As KEYBDINPUT
    <FieldOffset(0)> Public hi As HARDWAREINPUT
End Structure

Answer 8

@Eyal - hey, thanks for the idea; it never occurred to me that a delta of 0,0 might work. I've added that option as "Zen jiggle" to 1.2 (leaving the original in also, for those people who get nervous when they can't actually see it working).