The ChangeDisplaySettings function changes the display settings to the specified graphics mode.
LONG ChangeDisplaySettings(
| LPDEVMODE lpDevMode, | |
| DWORD dwflags | |
| ); |
Parameters
lpDevMode
Pointer to a DEVMODE structure that describes the graphics mode to switch to. The dmSize member must be initialized to the size, in bytes, of the DEVMODE structure. The following fields in the DEVMODE structure are used:
| Member | Meaning |
| dmBitsPerPel | Bits per pixel |
| dmPelsWidth | Pixel width |
| dmPelsHeight | Pixel height |
| dmDisplayFlags | Mode flags |
| dmDisplayFrequency | Mode frequency |
In addition to setting a value in one or more of the preceding DEVMODE members, you must also set the appropriate flags in the dmFields member. The flags indicate which members of the DEVMODE structure are used for the display settings change. If the appropriate bit is not set in dmFields, the display setting will not be changed. Set one or more of the following flags:
| Flag | Meaning |
| DM_BITSPERPEL | Use the dmBitsPerPel value. |
| DM_PELSWIDTH | Use the dmPelsWidth value. |
| DM_PELSHEIGHT | Use the dmPelsHeight value. |
| DM_DISPLAYFLAGS | Use the dmDisplayFlags value. |
| DM_DISPLAYFREQENCY | Use the dmDisplayFrequency value. |
If lpDevMode is NULL, all the values currently in the registry will be used for the display setting. Passing NULL for the lpDevMode parameter is the easiest way to return to the default mode after a dynamic mode change.
dwflags
Indicates how the graphics mode should be changed. May be one of the following:
| Flag | Meaning |
| 0 | The graphics mode for the current screen will be changed dynamically. |
| CDS_UPDATEREGISTRY | The graphics mode for the current screen will be changed dynamically and the graphics mode will be updated in the registry. The mode information is stored in the USER profile. |
| CDS_TEST | The system tests if the requested graphics mode could be set. |
If CDS_UPDATEREGISTRY is specified and it is possible to change the graphics mode dynamically, the information is stored in the registry and DISP_CHANGE_SUCCESSFUL is returned. If it is not possible to change the graphics mode dynamically, the information is stored in the registry and DISP_CHANGE_RESTART is returned.
Windows NT: If the information could not be stored in the registry, the graphics mode is not changed and DISP_CHANGE_NOTUPDATED is returned.
Specifying CDS_TEST allows an application to determine which graphics modes are actually valid, without causing the system to change to that graphics mode.
Return Values
Returns one of the following values:
| Value | Meaning |
| DISP_CHANGE_SUCCESSFUL | The settings change was successful. |
| DISP_CHANGE_RESTART | The computer must be restarted in order for the graphics mode to work. |
| DISP_CHANGE_BADFLAGS | An invalid set of flags was passed in. |
| DISP_CHANGE_FAILED | The display driver failed the specified graphics mode. |
| DISP_CHANGE_BADMODE | The graphics mode is not supported. |
| DISP_CHANGE_NOTUPDATED | Windows NT only: Unable to write settings to the registry. |
Remarks
Using the DEVMODE returned by the EnumDisplaySettings function ensures that the DEVMODE passed to ChangeDisplaySettings is valid and contains only values supported by the display driver.
When the display mode is changed dynamically, the WM_DISPLAYCHANGE message is sent to all running applications with the following message parameters:
| Parameters | Meaning |
| wParam | New bits per pixel |
| LOWORD(lParam) | New pixel width |
| HIWORD(lParam) | New pixel height |
See Also