Built-in Accessibility Features

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The built-in accessibility features are extensions to the operating system. These features affect the behavior of the system regardless of which applications are running.

Win32 supports the following built-in accessibility features.

Feature Description
AccessTimeout Enables a user to specify a time-out interval after which system-wide accessibility features are automatically disabled. The AccessTimeout feature is intended for computers that are shared by several users with different preferences. Each individual can use hot keys or the Ease of Access Center in Control Panel to enable preferred features. The accessibility time-out period is the length of time that must pass without keyboard and mouse input before the operating system automatically turns off accessibility features. The accessibility features affected by the time out are FilterKeys, MouseKeys, StickyKeys, and ToggleKeys, and high contrast. The ACCESSTIMEOUT structure defines the parameters for this feature.
FilterKeys Enables control of keyboard properties, such as the amount of time before a keystroke is accepted as input and the amount of time before a keystroke begins to repeat. The FilterKeys feature also provides sound feedback when a key is pressed and when it is accepted as input. The FILTERKEYS structure defines the parameters for this feature.
MouseKeys Enables the user to control the mouse pointer using the numeric keypad. The MOUSEKEYS structure defines the parameters for this feature.
SerialKeys Enables the user to provide input using an alternate input device attached to the computer's serial port. This feature is designed for users who are unable to use the computer's standard keyboard and mouse. The SERIALKEYS structure defines the parameters for this feature.
SoundSentry Displays a visual signal when a sound is generated by a Microsoft Win32-based application or an Microsoft MS-DOS application running in a window. The SOUNDSENTRY structure defines the parameters for this feature, including the address of the SoundSentryProc callback function.
StickyKeys Enables the user to type key combinations, such as CTRL+ALT+DEL, in sequence rather than at the same time. The STICKYKEYS structure defines the parameters for this feature.
ToggleKeys Provides sound feedback when the user turns on or off the CAPS LOCK, NUM LOCK, or SCROLL LOCK keys. The TOGGLEKEYS structure defines the parameters for this feature.

 

The SystemParametersInfo function provides the programming interface to the built-in accessibility features. This function is useful in Control Panel applications or other programs that allow the user to customize the environment. The SystemParametersInfo function can perform the following tasks:

  • Query the system to determine the availability and current state of a specified built-in accessibility feature.
  • Enable a feature and specify parameters that control its behavior.
  • Disable a feature.
  • Enable a hot key that allows the user to enable or disable a feature.

For each of the built-in features, Win32 defines a structure that applications use with SystemParametersInfo to query or set the parameters of the feature.

An application can use SystemParametersInfo to enable or disable a feature directly. For some of the features, SystemParametersInfo can enable a hot key or key combination so the user can toggle the state of a feature. There are no hot keys for the SerialKeys or SoundSentry features, or for the ShowSounds parameter. The following accessibility features have hot keys.

Feature Description
FilterKeys Hold down the RIGHT SHIFT key for eight seconds to toggle the FilterKeys feature on or off. Holding down the RIGHT SHIFT key for 12 seconds enables FilterKeys using the most conservative values for the iBounceMSec member of the FILTERKEYS structure. Holding down the RIGHT SHIFT key for 16 seconds enables FilterKeys using the most conservative values for the iWaitMSec member of the FILTERKEYS structure..
MouseKeys Press LEFT ALT + LEFT SHIFT + NUM LOCK.
StickyKeys Press the SHIFT key 5 times.
ToggleKeys Hold down the NUM LOCK key for 5 seconds.
High contrast mode Press LEFT ALT + LEFT SHIFT + PRINT SCREEN.