IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS control code

Retrieves the supported backlight levels.

To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL DeviceIoControl(
  (HANDLE) hDevice,                // handle to device
  IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS,  // dwIoControlCode
  NULL,                            // lpInBuffer
  0,                               // nInBufferSize
  (LPVOID) lpOutBuffer,            // output buffer
  (DWORD) nOutBufferSize,          // size of output buffer
  (LPDWORD) lpBytesReturned,       // number of bytes returned
  (LPOVERLAPPED) lpOverlapped      // OVERLAPPED structure
);

Parameters

hDevice

A handle to the \\.\LCD device. To retrieve a device handle, call the CreateFile function.

dwIoControlCode

The control code for the operation. This value identifies the specific operation to be performed and the type of device on which to perform it. Use IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS for this operation.

lpInBuffer

Not used with this operation; set to NULL.

nInBufferSize

Not used with this operation; set to zero.

lpOutBuffer

A pointer to a buffer that receives an array of the available power levels. This buffer should be 256 bytes long.

nOutBufferSize

The size of the output buffer, in bytes.

lpBytesReturned

A pointer to a variable that receives the size, in bytes, of output data returned.

If the output buffer is too small to return any data, then the call fails, GetLastError returns the error code ERROR_INSUFFICIENT_BUFFER, and the returned byte count is zero.

If the output buffer is too small to hold all of the data but can hold some entries, then the operating system returns as much as fits, the call fails, GetLastError returns the error code ERROR_MORE_DATA, and lpBytesReturned indicates the amount of data returned. Your application should call DeviceIoControl again with the same operation, specifying a new starting point.

If lpOverlapped is NULL (nonoverlapped I/O), lpBytesReturned cannot be NULL.

If lpOverlapped is not NULL (overlapped I/O), lpBytesReturned can be NULL. If this is an overlapped operation, you can retrieve the number of bytes returned by calling the GetOverlappedResult function. If hDevice is associated with an I/O completion port, you can get the number of bytes returned by calling the GetQueuedCompletionStatus function.

lpOverlapped

A pointer to an OVERLAPPED structure.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, lpOverlapped must point to a valid OVERLAPPED structure. In this case, the operation is performed as an overlapped (asynchronous) operation. If the device was opened with the FILE_FLAG_OVERLAPPED flag and lpOverlapped is NULL, the function fails in unpredictable ways.

If hDevice was opened without specifying the FILE_FLAG_OVERLAPPED flag, lpOverlapped is ignored and DeviceIoControl does not return until the operation has been completed, or until an error occurs.

Return value

If the operation completes successfully, DeviceIoControl returns a nonzero value.

If the operation fails or is pending, DeviceIoControl returns zero. To get extended error information, call GetLastError.

Remarks

Each element in the lpOutBuffer array is one byte in length. Therefore, upon return, the lpBytesReturned parameter indicates the number of supported levels. Each level is a value from 0 to 100. The larger the value, the brighter the backlight. All levels are supported whether the power source is AC or DC.

The header file used to build applications that include this functionality, Ntddvdeo.h, is included in the Microsoft Windows Driver Development Kit (DDK). For information on obtaining the DDK, see https://www.microsoft.com/whdc/devtools/ddk/default.mspx.

Alternatively, you can define this control code as follows:

#define IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS \
  CTL_CODE(FILE_DEVICE_VIDEO, 0x125, METHOD_BUFFERED, FILE_ANY_ACCESS)

Requirements

See also

Backlight Control Interface

DeviceIoControl