DPI-related APIs and registry settings
If you need to perform deployment customizations, the following sections explain the registry keys and system parameters that your post-installation scripts might need to access.
In this topic:
Primary display native resolution
Table 1 Windows 8.1 Scaling Levels, while by no means exhaustive, provides information on the Windows 8.1 scaling level for a number of common displays. Panel DPI indicates the physical pixel density of the panel, and Scaling level indicates the scale factor that will be used for this display.
Table 1 Windows 8.1 Scaling Levels
|Display size||Display resolution||Horizontal (pixels)||Vertical (pixels)||Panel DPI||Scaling level|
To programmatically find this information for any device, you can write a utility program that reports back data. The native primary resolution is retrieved by calling the API GetDeviceCaps() function, using the hdc for the desktop and the HORZRES and VERZRES indices:
// Get desktop dc desktopDc = GetDC(NULL); // Get native resolution horizontalResolution = GetDeviceCaps(desktopDc,HORZRES); verticalResolution = GetDeviceCaps(desktopDc,VERZRES);
For more information about GetDC, see GetDC() function.
Primary display DPI scale factor
Similarly, you can get the pixel density by using the LOGPIXELSX and LOGPIXELSY indices:
// Get desktop dc desktopDc = GetDC(NULL); // Get native resolution horizontalDPI = GetDeviceCaps(desktopDc,LOGPIXELSX); verticalDPI = GetDeviceCaps(desktopDc,LOGPIXELSY);
These results are returned in a coordinate system in which 96 corresponds to 100%, as shown in Table 2 DPI Scale Factors.
Table 2 DPI Scale Factors
This API will return different results depending on the DPI awareness mode of your application. Configuring the awareness mode requires adding XML to the application manifest, as detailed below:
|DPI Awareness Mode||Manifest Setting||Returned Value|
|None||None||96 for all displays, regardless of the scale factor|
|System DPI Aware||<dpiAware>True</dpiAware>||The DPI of the primary display at the time the Windows session was started (when the user first logged in to Windows)|
|Per-Monitor DPI Aware||<dpiAware>True/PM</dpiAware>||The DPI of the primary display at the time the Windows session was started (when the user first logged in to Windows). To obtain the DPI of the display that the application is located on, use GetWindowDpi() or GetDpiForMonitor()|
For more information about this manifest setting, see SetProcessDPIAware function.
The Control Panel\ Appearance and Personalization\Display user interface (UI) includes a checkbox: Let me choose one scaling level for all my displays, which controls whether the system applies a single scale factor to all displays (as in Windows 8 and earlier versions of Windows), or different scale factors that take into account the pixel density of each display (the Windows 8.1 default). This checkbox configures the HKCU\Control Panel\Desktop\Win8DpiScaling registry key in Windows 8.1.
Table 3 HKCU\Control Panel\Desktop\Win8DpiScaling Values
|0||Different scale factors for each display: Windows 8.1 default.Content that is moved from one display to another will be the right size, but can be bitmap-scaled.|
|1||Same scale factor is applied to all displays: Windows 8 and earlier Windows versions behavior. Content that is moved from one display to another might be the wrong size.|
Scaling override in Windows 8.1 scaling mode
When the Let me choose one scaling level for all my displays checkbox is cleared and the system is running in the Windows 8.1 scaling mode, the user is provided with a slider that lets them override the current scale factors, from Smaller, to Medium, to Larger. This setting is configured in the HKCU\Control Panel\Desktop\DesktopDPIOverride registry key.
Table 4 HKCU\Control Panel\Desktop\DesktopDPIOverride Values
|<0||Reduce each display scale factor from the default by this value (for example, if the default was 150% scaling, -1 corresponds to 125%, -2 to 100%).|
|0||Use the default value for each display.|
|0>||Increase each display factor by this value (using the previous example, +1 corresponds to 200% scaling).|
All display scale factors in this mode are constrained to be one of these four values: 100%, 125%, 150%, 200%. In addition, after scaling is applied, applications expect to have at least 720 effective lines of resolution (that is, the physical vertical resolution of the display divided by the scale factor); this can further limit the range of allowed display scale factors. Table 5 Display Values shows which values are allowed for different sized displays:
Table 5 Display Values
|Vertical lines||Supported scale factors|
|>= 900 and <1080||100%, 125%|
|>=1080 and <1440||100%, 125%, 150%|
|>=1440||100%, 125%, 150%, 200%|
System-wide scale factor in Windows 8 scaling mode
When the Let me choose one scaling level for all my displays checkbox is checked, the user can specify a scale factor that applies to all displays, regardless of each display’s pixel density. By using the custom setting, the user can select values other than 100%, 125%, 150%, 200%, although they are limited to the range (100%-500%). This setting is configured in the HKCU\Control Panel\Desktop\LogPixels registry key.
Table 6 HKCU\Control Panel\Desktop\LogPixels Values
|96||100% scaling on every display|
|120||125% scaling on every display|
|144||150% scaling on every display|
|192||200% scaling on every display|
|<other>||<other>*100/96 scaling on every display|