none
Backlight Control Interface

    Question

  • My apologies for bothering with this topic once again.

    I know it has been discussed in various forums but this seems to remain one of the big mysteries of the universe ...

    I couldn't figure out a better location for this question, since this forum is Hardware Development related.

    The question is simple: what is required by the Windows 2000 Display Driver Model (or the graphics drivers supporting that model) in order to make the Video Port driver capable of handling the Backlight Control Interface calls

        IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS
        IOCTL_VIDEO_QUERY_DISPLAY_BRIGHTNESS
        IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS

    corrrectly?

    As OEM we provided a graphics infrastructure for Vista and above which makes the Backlight Control Interface work perfectly. (We do not need it for VST/W7 but it works anyway).

    However, if I call IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS on XP, I get STATUS_SUCCESS but the list of supported values is empty (0 elements).

    The WDK docs state that these calls are handled entirely by the system-supplied video port driver, NOT the video miniport.

    So there must be a way to tell the video port driver, what levels to support and how to set.

    Any hint/thought appreciated.

    Thanks, Gernot

     

    Tuesday, November 15, 2011 6:01 PM

Answers

All replies

  • As I recall, XP and Win2K only supported changing the backlight levels on laptops, because it used an ACPI method to get the supported backlight levels.  WDDM (Vista and later) support changing the backlight on non-laptops through the monitor driver http://msdn.microsoft.com/en-us/library/ff569755(v=vs.85).aspx

     -Brian

     


    Azius Developer Training www.azius.com Windows device driver, internals, security, & forensics training and consulting.
    Tuesday, November 15, 2011 11:18 PM
  • Brian,

    Thanks for reponding.

    BUT:

    A) We do have ACPI methods in place but it does not work with XP (as it does with W7).

    B) I did some testing on a notebook computer with brightness keys and working brightness control on XP via a propietary(?) mechanism. However, trying the Backlight Control Interface is not successful. (The result is identical: I get an empty list for IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS).

    Can MS (anybody out there?) confirm it is supported in XP or officially state that it is not?

    Thanks,
    Gernot

    Thursday, November 17, 2011 1:53 PM
  • Hi Everyone,

    I have a reflective laptop display called pixel Qi, which reflect ambient light and good for my eye. I want to install it on a different laptop with a better cpu. 

    Question 1:

    how do I turn off the lcd backlight under windows?

    I have searched this for a long time, and it is possible in linux using a command called setpci, the other way is to put a switch in the circuit. 

    Question 2:

    The pixel qi resolution is 1024X600 (10.1"), and the cable is 40 pin lvds, can I use this screen on a 13" or higher laptop? Will I damage it if the native resolution of that laptop is not 1024X600?

    Thank you very much!

    Eric

    Friday, July 05, 2013 2:05 AM
  • Not a driver develop question, please don't hijack a thread

    d -- This posting is provided "AS IS" with no warranties, and confers no rights.

    Friday, July 05, 2013 3:11 AM