Brightness Control in WDDM
Updated: July 29, 2008
File name: Brightness.docx
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In the Windows Vista operating system, brightness controls are implemented in the operating system-supplied monitor driver, Monitor.sys. The monitor driver implements a Windows Management Instrumentation (WMI) interface to let applications-such as the operating system's brightness slider-interact with the brightness level.
The monitor driver registers with the operating system device power policy so that brightness levels respond to changes in power policy. The monitor driver registers for Advanced Configuration and Power Interface (ACPI) notifications to process ACPI-based brightness shortcut keys. For compatibility with the Windows XP Display Driver Model, the monitor driver implements the IOCTL-based brightness controls.
Windows exposes brightness control by using publicly documented APIs. Original equipment manufacturers (OEMs) can use this interface to expose the control of brightness to the end-user through user interface (UI) in their value-added software. The Brightness slider in the Windows Vista Mobility Center is an example of a client that uses these interfaces. Another way to control brightness include OEM shortcut keys, which interact with the system BIOS. Windows Vista can also automatically change the brightness of the panel, depending on the power policy settings that the Administrator applied.
Each of these control mechanisms exercises a slightly different path of the graphics stack. However, brightness can be controlled through four scenarios, each of which is discussed in this paper.
This information applies to the Windows Vista operating system.
Included in this paper: