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Windows 7 Brightness Control for Integrated Displays

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Windows 7 Brightness Control for Integrated Displays

    Windows 7 Brightness Control for Integrated Displays

    January 9, 2009

    Abstract

    This paper provides information about integrated display brightness control for the Windows? family of operating systems. It provides guidelines for system manufacturers and firmware developers to expose brightness control infrastructure to Windows. The new brightness control user experiences for Windows 7 are discussed. Additionally, this paper provides power policy configuration information, including new policies for the adaptive display brightness feature and information on how to observe brightness control changes by using the PwrTest utility. This information applies to the Windows 7 operating system.

    References and resources discussed here are listed at the end of this paper. For the latest information, see:

     http://www.microsoft.com/whdc/system/pnppwr/powermgmt/BrightnessCtrl.mspx

    Windows 7 Brightness Control for Integrated Displays - 2

    Disclaimer: This is a preliminary document and may be changed substantially prior to final commercial release of the software described herein. The information contained in this document represents the current view of Microsoft Corporation on the issues discussed as of the date of publication. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information presented after the date of publication. This White Paper is for informational purposes only. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS DOCUMENT. Complying with all applicable copyright laws is the responsibility of the user. Without limiting the rights under copyright, no part of this document may be reproduced, stored in or introduced into a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of Microsoft Corporation. Microsoft may have patents, patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in this document. Except as expressly provided in any written license agreement from Microsoft, the furnishing of this document does not give you any license to these patents, trademarks, copyrights, or other intellectual property. Unless otherwise noted, the example companies, organizations, products, domain names, e-mail addresses, logos, people, places and events depicted herein are fictitious, and no association with any real company, organization, product, domain name, email address, logo, person, place or event is intended or should be inferred. ? 2009 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Server, Windows Vista, and PowerPoint are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries. The names of actual companies and products mentioned herein may be the trademarks of their respective owners.

    Document History

     Date Change

    January 9, 2009 First publication

January 9, 2009 ? 2009 Microsoft Corporation. All rights reserved.

    Windows 7 Brightness Control for Integrated Displays - 3

    Contents

    Introduction ............................................................................................................... 4 Brightness Control User Experiences........................................................................... 4 Power Options........................................................................................................ 5 Windows Mobility Center ....................................................................................... 8 Hardware Hot Keys ................................................................................................. 8 Battery Meter Brightness Warnings ........................................................................ 9 Brightness Control Platform Infrastructure ................................................................. 9 ACPI-Based Brightness Control Interface ................................................................ 9 WDDM Driver DDI Brightness Control Interface .................................................... 10 Hot Key Integration .............................................................................................. 11 Fading Transitions ................................................................................................ 11 Brightness Control Policies and Actions .................................................................... 12 Default Display Brightness Policies ....................................................................... 12 Adaptive Display Brightness Policies ..................................................................... 12 Advanced Adaptive Display Brightness Policies ..................................................... 13 Best Practices for Brightness Control Policy Configuration ........................................ 14 Best Practices for Software Developers..................................................................... 15 Integration with Ambient Light Sensor Devices ......................................................... 15 Validation of Platform Brightness Control ................................................................. 15 The PwrTest MONITOR Scenario ........................................................................... 15 Observation of Brightness Level Changes with the MONITOR Scenario ................. 16

    Call to Action ............................................................................................................ 18 Resources ................................................................................................................. 19

January 9, 2009 ? 2009 Microsoft Corporation. All rights reserved.

    Windows 7 Brightness Control for Integrated Displays - 4

    Introduction

    During ordinary use, the integrated display in most portable computers is the greatest consumer of power. To reduce power consumption and extend battery life, Windows? provides an infrastructure for controlling the brightness of the display. Windows 7 simplifies the user experience for brightness control and configuration. Brightness controls are available in the Windows Mobility Center, the Control Panel Power Options application, and hot keys on the system keyboard. User adjustments to the brightness level are now applied to the current power policy, which preserves the user’s brightness level adjustment across sleep, resume, shutdown, and restart transitions. After a period of user inactivity, the display brightness automatically dims to help extend battery life.

    Windows supports two ways to integrate brightness control: Windows Display Driver Model (WDDM) miniport device driver interfaces (DDIs) and Advanced Configuration and Power Interface (ACPI) firmware control methods. ACPI control methods are the preferred implementation solution for new platforms. The underlying brightness control infrastructure is configured by using power policy settings. System manufacturers can customize these settings based on the target platforms or display technologies.

    System manufacturers and firmware developers should review this paper for details on the Windows brightness control infrastructure, new user experiences, and power policy configuration details for display brightness.

    Brightness Control User Experiences

    Windows 7 improves the brightness control configuration user experience by simplifying the interaction between the various methods to set the display brightness. Adjustments to the display brightness that a user makes through Windows Mobility Center or keyboard hot keys now persist across system power-state transitions (standby and resume). A user can also easily adjust the display brightness level by using a new slider control in the Control Panel Power Options application. If the

    display brightness is set to a level that is greater than the default display brightness of the On battery policy for the active power plan, a warning appears in the battery meter to advise the user of the effect of the display brightness setting on the battery life of a portable computer.

    January 9, 2009 ? 2009 Microsoft Corporation. All rights reserved.

    Windows 7 Brightness Control for Integrated Displays - 5

    Power Options

    The Control Panel Power Options application is the user’s primary interaction point for setting the display brightness. In Windows 7, a Display brightness adjustment

    slider is now available at the bottom of Power Options, as shown in Figure 1.

Figure 1. The Control Panel Power Options application

    The Display brightness adjustment slider sets the brightness level for the current power plan.

    January 9, 2009 ? 2009 Microsoft Corporation. All rights reserved.

    Windows 7 Brightness Control for Integrated Displays - 6 Similar to Windows Vista?, in Windows 7 users can set the default brightness both for

    when the computer is running On battery and when it is Plugged in for each power

    plan. This functionality is available in Power Options by clicking Change plan settings

    for one of the power plans. This displays the Edit plan settings page, as shown in

    Figure 2.

Figure 2. The Edit plan settings page in Power Options

    January 9, 2009 ? 2009 Microsoft Corporation. All rights reserved.

    Windows 7 Brightness Control for Integrated Displays - 7

    New for Windows 7 are controls to configure adaptive display brightness. These controls set the amount of idle time after which Windows automatically reduces the display brightness to a lower brightness level to save power. These controls are available in the Advanced settings dialog box, which users can open by clicking the

    Change advanced power settings link on the Edit plan settings page. The adaptive

    display brightness controls are under the Display node, as shown in Figure 3.

Figure 3. Power Options Advanced settings dialog box

    January 9, 2009 ? 2009 Microsoft Corporation. All rights reserved.

    Windows 7 Brightness Control for Integrated Displays - 8

    Windows Mobility Center

    For Windows 7, the Display brightness slider remains in Windows Mobility Center, as

    shown in Figure 4. Users can access Windows Mobility Center from the battery

    meter icon shortcut menu or by pressing the ; +X shortcut key.

Figure 4. Windows Mobility Center

    In earlier versions of Windows, if users adjusted the display brightness through the Windows Mobility Center, that setting was in effect only until the system changed its power source (switched between running on battery and being plugged in) or until the system changed its power state (sleep or restart). This behavior is different in Windows 7. If users adjust the display brightness through Windows Mobility Center,

    the new brightness level is applied to the current power policy. Therefore, when the system sleeps, resumes, or restarts, the display continues to use the same brightness level that the user set.

    Hardware Hot Keys

    Many portable computers include hardware buttons or hot keys for changing the display brightness. Typically, users access these hot keys by pressing a function (Fn) button in combination with another key on the keyboard.

    Similar to the update to Windows Mobility Center, if the user adjusts the display

    brightness by using hot keys in Windows 7, the new brightness level is applied to the current power policy. For example, if the user changes the display brightness to 80 percent by using the hot keys, the 80-percent setting is stored as either the On

    battery or Plugged in brightness level value in the current power plan, depending on whether the system is running on battery or is plugged in at the time that the user changes the display brightness.

    January 9, 2009 ? 2009 Microsoft Corporation. All rights reserved.

    Windows 7 Brightness Control for Integrated Displays - 9

    Battery Meter Brightness Warnings

    In Windows 7, the battery meter displays a warning if the system is operating on battery and the display brightness is set to a level that is greater than the default display brightness of the battery policy for the active power plan, as shown in Figure 5. This warning helps users understand that reducing the display brightness is a simple step to extend the battery life of a portable computer.

Figure 5. Battery meter brightness level warning

    System manufacturers can adjust the default values for the display brightness policy for their systems to target the many display types and brightness levels in the Windows ecosystem. The display brightness warning is based on the default value of the On battery display brightness policy in the current power plan. If a system manufacturer does not customize the default values for the display brightness policy, the default value for the On battery display brightness is 30 percent.

    Brightness Control Platform Infrastructure

    Any platform that exposes display brightness control functionality through a method that is compatible with Windows Vista is also compatible with Windows 7. A platform exposes its display brightness control functionality by using either ACPI control methods or WDDM miniport DDIs. We recommend that system manufacturers use ACPI control methods and that they support a minimum of 25 discrete display brightness levels.

    The rest of this section of this paper summarizes the platform driver and firmware requirements for supporting brightness control functionality. For more information, see Brightness Control in WDDM on the WHDC Web site.

    ACPI-Based Brightness Control Interface

    System manufacturers should expose brightness control functionality by using the ACPI control methods under the output device for the integrated display. The brightness control methods can be applied to portable computers and all-in-one desktop systems that have an integrated display. For more information about ACPI brightness control methods, see Appendix B in the ACPI specification. January 9, 2009 ? 2009 Microsoft Corporation. All rights reserved.

    Windows 7 Brightness Control for Integrated Displays - 10

    The firmware must support all the ACPI brightness control methods in Table 1. Table 1. ACPI Brightness Control Methods

    Description Method

    name

    _BQC Enables the operating system to query the current display brightness level.

    _BCL Enumerates a list of supported brightness levels in units of percentage of

    maximum brightness.

    _BCM Enables the operating system to set the display brightness level.

    The _BCL control method returns a list of the supported brightness levels in units of the percentage of the maximum brightness and the firmware-provided default values for the display brightness when the system is running on battery and is plugged-in. Note that Windows ignores the firmware-provided default values and, without system manufacturer customization of the power policy, uses a Plugged in default

    value of 100 percent and an On battery default value of 30 percent.

    We recommend that firmware developers support at least 25 discrete display brightness levels in the _BCL control method. Additional brightness levels help provide an optimal user experience if the user adjusts the display brightness by using the Windows Mobility Center slider and if the user has a system that is equipped with an ambient light sensor (ALS) device.

    WDDM Driver DDI Brightness Control Interface

    Brightness controls are implemented in the monitor driverMonitor.systhat is

    included with Windows. The Windows monitor driver calls the display miniport driver's DxgkDdiQueryInterface function for the first video target in the system that is identified as having output technology that connects to an internal display device. This video target has the InterfaceTechnology member of the

    DXGK_VIDEO_OUTPUT_CAPABILITIES structure set to D3DKMDT_VOT_INTERNAL. This call queries for the brightness control interface that is identified by GUID_DEVINTERFACE_BRIGHTNESS and DXGK_BRIGHTNESS_INTERFACE_VERSION_1. WDDM miniport drivers that expose brightness control functionality by using the GUID_DEVINTERFACE_BRIGHTNESS interface should support a minimum of 25 discrete display brightness levels. These levels let users smoothly adjust the display brightness by using slider controls and provides fine-grained adjustment for platforms that are equipped with an ALS device.

    If the WDDM miniport driver does not support the brightness control interface, the monitor driver uses the ACPI control methods_BCL, _BCM, and _BQCif they are

    exposed by the platform firmware.

    To avoid problems that might occur if both the system firmware and the monitor driver control the brightness of the display, the display miniport driver should set bit 2 of the argument to the _DOS method. Setting this bit notifies the system firmware that it should not perform any automatic display brightness changes. The WDDM driver must set this particular bit because it controls the _DOS method. The other bits in the _DOS method control the behavior of the firmware in response to the display switch hot keys.

    January 9, 2009 ? 2009 Microsoft Corporation. All rights reserved.

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