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  1. #1
    Join Date
    Sep 2008

    Question WmiSetBrightness method not supported (.Net 4.0, Winforms, Windows 7).

    I'm trying to adjust the brightness (not the gamma ramp values) of the monitor using WmiSetBrightness method but the system throws a ManagementException during runtime saying 'Not supported'. I have seen a lot of people using this concept and running successfully. So what's wrong with mine? Is it because this is not supported in Windows 7 Ultimate; on which I'm working?
    My Code follows:

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1_Click
    		Dim mclass As New ManagementClass("WmiMonitorBrightnessMethods")
    		mclass.Scope = New ManagementScope("\\.\root\wmi")
    		Dim instances As ManagementObjectCollection = mclass.GetInstances()
    		For Each instance As ManagementObject In instances
    			Dim brightness As Byte = 50 'In percent.
    			Dim timeout As UInt64 = 1 'In seconds.
    			Dim args As Object() = New Object() {brightness, timeout}
    			instance.InvokeMethod("WmiSetBrightness", args) 'Only work on the first object.
    			Exit For
    	Catch ex As ManagementException
    	End Try
    End Sub
    To test if the instances are literally obtained, I commented the foreach part and tried to print the count of the instances using instances.Count.ToString() through a MessageBox but still the exception is thrown.

    As an alternative, I tried to work with DeviceIOControl and IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS but of no success. The code follows:

    Public Class Form1
        Private Declare Auto Function CreateFile Lib "kernel32" _
        (ByVal lpFileName As String, ByVal dwDesiredAccess As Int32, _
         ByVal dwShareMode As Int32, ByVal lpSecurityAttributes As IntPtr, _
         ByVal dwCreationDisposition As Int32, _
         ByVal dwFlagsAndAttributes As Int32, ByVal hTemplateFile As IntPtr) As IntPtr
        Const GENERIC_READ As Int32 = &H80000000%
        Const SHARE_ALL As Int32 = &H7%
        Const OPEN_EXISTING As Int32 = &H3%
        Const IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS As Integer = &H23049C%
        Private Structure BRIGHTNESS
            Public ucDisplayPolicy As Byte
            Public ucACBrightness As Byte
            Public ucDCBrightness As Byte
        End Structure
        Private Declare Auto Function DeviceIoControl Lib "kernel32" _
         (ByVal hDevice As IntPtr, ByVal dwIoControlCode As Int32, _
         ByRef lpInBuffer As BRIGHTNESS, ByVal nInBufferSize As Int32, _
         ByVal lpOutBuffer As IntPtr, ByVal nOutBufferSize As Int32, _
         ByRef lpBytesReturned As Int32, ByVal lpOverlapped As IntPtr) As Boolean
        Private Declare Auto Function CloseHandle Lib "kernel32" _
         (ByVal hObject As IntPtr) As Boolean
        ''' <summary>
        ''' Set the brightness of the screen.
        ''' </summary>
        ''' <param name="Brightness">The Screen Brightness.</param>
        Private Sub SetBrightness(ByRef Brightness As BRIGHTNESS)
            ' Get the display.
            Dim pDisplay As IntPtr = _
             CreateFile("\\.\LCD", GENERIC_READ, SHARE_ALL, IntPtr.Zero, OPEN_EXISTING, 0, IntPtr.Zero)
            ' Set the brightness.
            DeviceIoControl(pDisplay, IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS, _
            Brightness, Runtime.InteropServices.Marshal.SizeOf(Brightness), IntPtr.Zero, 0, Nothing, IntPtr.Zero)
            ' Close the handle.
        End Sub
        Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
            Dim brightness As BRIGHTNESS
            ' The brightness on DC Power.
            brightness.ucDCBrightness = 100
            ' The Brightness on AC Power.
            brightness.ucACBrightness = 100
            ' Call the function.
        End Sub
    End Class
    For some reason DeviceIoControl always returns False.
    Please assist in sorting these out.

    BTW, this is not about modifying gamma ramp values using SetDeviceGammaRamp, as it adjusts the contrast of the monitor; not the brightness. So, any post on that matter won't be of much help.


  2. #2
    Join Date
    Jul 2001
    Sunny South Africa

    Re: WmiSetBrightness method not supported (.Net 4.0, Winforms, Windows 7).

    Any particular reason why you don't want to use the Gamma values? Because as far as I know, you do need to change those values. Search on this forum for "monitor" or "monitor brightness". There is thread done by me and the legend TT(n) about Monitor brightness. We have worked out a solution that works on all Operating Systems

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