The high-contrast option indicates whether an application should use a high contrast between the colors used for foreground and background visuals.

The user can control the setting of the high-contrast option by using the Displaytab of the AccessibilityControl Panel application or another application for customizing the environment. Applications use the SPI_GETHIGHCONTRAST and SPI_SETHIGHCONTRAST flags with the SystemParametersInfofunction to get and set the high-contrast option.

Both when an application initializes and when it processes WM_SYSCOLORCHANGE messages, the application should determine the state of the high-contrast option. To make this determination, the application should call SystemParametersInfowith the uiActionparameter set to SPI_GETHIGHCONTRAST flag and the uiParamparameter set to the size of the HIGHCONTRASTstructure to obtain a HIGHCONTRASTstructure. If the value of the dwFlagsmember of the HIGHCONTRASTstructure includes the HCF_HIGHCONTRASTON flag, then the high-contrast option is enabled. When the high-contrast option is enabled, an application should perform the following tasks to ensure maximum visibility of the user interface for users with low vision:

• Map all colors to a single pair of foreground and background colors. Use the GetSysColorfunction to determine the appropriate foreground and background colors, using either a combination of COLOR_WINDOWTEXT and COLOR_WINDOW or a combination of COLOR_BTNTEXT and COLOR_BTNFACE. The GetSysColorfunction returns the colors that the user selected through the AccessibilityControl Panel.
  
  
• Omit any bitmapped images that you display in the background behind text. Such images visually distract a user who needs high contrast.
  
  
• Draw images that you would usually draw in multiple colors by using only the foreground and background colors selected for text.
  
  

An application can turn on the high-contrast option by calling SystemParametersInfowith uiActionset to SPI_SETHIGHCONTRAST, uiParamset to the size of the HIGHCONTRASTstructure, and the pvParamparameter set to a pointer to a HIGHCONTRASTstructure that contains the high-contrast parameters that you want to use. You should set the HCF_HIGHCONTRASTON flag in the dwFlagsmember of the ACCESSTIMEOUTstructure that you pass to SystemParametersInfo.

The following code example shows how to enable the high-contrast option and set the color scheme to high-contrast white.

	Copy Code
HIGHCONTRAST hcf; BOOL bSuccess; // Fill in the members of the HIGHCONTRAST structure. hcf.cbSize = sizeof(HIGHCONTRAST); hcf.dwFlags = (HCF_AVAILABLE | HCF_HIGHCONTRASTON); hcf.lpszDefaultScheme = TEXT("High Contrast White"); // Call SystemParametersInfo with the SPI_SETHIGHCONTRAST flag. bSuccess = SystemParametersInfo(SPI_SETHIGHCONTRAST, sizeof(HIGHCONTRAST), (LPVOID) &hcf, 0);

See Also