The following table provides some sample DPI values and associated scaling factors. To determine the scaling factor for a monitor, take the DPI value and divide by USER_DEFAULT_SCREEN_DPI. The base value of DPI is defined as USER_DEFAULT_SCREEN_DPI which is set to 96. For example, if a user is using multiple monitors and drags your window from a 96 DPI monitor to a 192 DPI monitor, your window will appear to be half as large with respect to other items on the 192 DPI monitor. If you do not do this, your window will grow or shrink with respect to everything else on the new monitor. In order to handle this message correctly, you will need to resize and reposition your window based on the suggestions provided by lParam and using SetWindowPos. You only need to use either the X-axis or the Y-axis value when scaling your application since they are the same. Currently, DPI awareness is tied to threads and individual windows rather than the entire application. Older versions of Windows required DPI awareness to be tied at the level of an application. For more information about the different types of awareness, see PROCESS_DPI_AWARENESS and DPI_AWARENESS.
It may be received on certain DPI changes if your top-level window or process is running as DPI unaware or system DPI aware, but in those situations it can be safely ignored. This message is only relevant for PROCESS_PER_MONITOR_DPI_AWARE applications or DPI_AWARENESS_PER_MONITOR_AWARE threads. If an application processes this message, it should return zero. The expectation is that apps will reposition and resize windows based on the suggestions provided by lParam when handling this message.
The values of the X-axis and the Y-axis are identical for Windows apps.Ī pointer to a RECT structure that provides a suggested size and position of the current window scaled for the new DPI. The LOWORD of the wParam contains the X-axis value of the new DPI of the window. The HIWORD of the wParam contains the Y-axis value of the new dpi of the window. This is the scale factor that the window should be scaling to for threads that are aware of DPI changes. The current DPI for a window always equals the last DPI sent by WM_DPICHANGED.
The following list indicates the possible causes for the change in DPI. There are multiple events that can cause the DPI to change. The DPI is the scale factor for a window. Sent when the effective dots per inch (dpi) for a window has changed.
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