Accessibility Parameters
The system maintains a set of accessibility parameters that indicate whether the user has special needs or preferences that require applications to change their default behavior. The user controls the state of these parameters, typically using the Accessibility Options Control Panel application. Control Panel applications or other programs that allow the user to customize the environment can use the SystemParametersInfo function to set the accessibility parameters.
If a user changes these parameters, the Control Panel sends the WM_SETTINGCHANGE message. Applications should respond to this message and use SystemParametersInfo to determine the state of the accessibility parameters. When an accessibility parameter is enabled, the application should modify its user interface, if necessary, to accommodate the user's preferences.
Win32 supports the following accessibility parameters.
| Parameter | Description |
|---|---|
| High contrast | Indicates that applications should provide high contrast between foreground and background visuals. |
| Keyboard Preference | Indicates that applications should display keyboard interfaces that would otherwise be hidden. |
| Screen Reader | Indicates that applications should provide textual information in situations where it would otherwise present the information graphically. |
| Captions and Audio Descriptions | Indicates that applications should also provide a visual alert or cue when it uses sound to convey important information, or provide and audio description for visual elements. |
| Client Area Animation | Indicates that applications should respect user preferences for displaying animation in the client area. |
| Message Duration | Indicates that applications that provide pop up notifications must monitor flags about message duration and adjust their notification length. |
The following system parameters are useful for accessibility applications. For more information, see SystemParametersInfo function.
| Parameter Group | Parameter |
|---|---|
| Desktop parameters | SPI_GETWORKAREA, SPI_SETWORKAREA |
| Input parameters | SPI_GETKEYBOARDCUES, SPI_GETKEYBOARDDELAY, SPI_GETKEYBOARDPREF, SPI_GETKEYBOARDSPEED, SPI_GETMESSAGEDURATION, SPI_GETMOUSE, SPI_GETMOUSEHOVERHEIGHT, SPI_GETMOUSEHOVERTIME, SPI_GETMOUSEHOVERWIDTH, SPI_GETMOUSESPEED, SPI_GETMOUSETRAILS, SPI_GETSNAPTODEFBUTTON, SPI_GETWHEELSCROLLLINES, SPI_SETDOUBLECLICKTIME, SPI_SETDOUBLECLKHEIGHT, SPI_SETDOUBLECLKWIDTH, SPI_SETKEYBOARDCUES, SPI_SETKEYBOARDDELAY, SPI_SETKEYBOARDPREF, SPI_SETKEYBOARDSPEED, SPI_SETMOUSE, SPI_SETMOUSEHOVERHEIGHT, SPI_SETMOUSEHOVERTIME, SPI_SETMOUSEHOVERWIDTH, SPI_SETMOUSESPEED, SPI_SETMOUSETRAILS, SPI_SETSNAPTODEFBUTTON, SPI_SETWHEELSCROLLLINES |
| UI effect parameters | SPI_GETMENUUNDERLINES, SPI_SETMENUUNDERLINES |
| Window parameters | SPI_GETCARETWIDTH, SPI_GETFOREGROUNDFLASHCOUNT, SPI_GETFOREGROUNDLOCKTIMEOUT, SPI_SETCARETWIDTH, SPI_SETDRAGHEIGHT, SPI_SETDRAGWIDTH, SPI_SETFOREGROUNDFLASHCOUNT, SPI_SETFOREGROUNDLOCKTIMEOUT |