GetScaleFactorForMonitor

The function `GetScaleFactorForMonitor` is a Windows API call designed to retrieve the scale factor of a specified display monitor. Introduced in Windows 8, this function is part of the Windows Graphics Device Interface (GDI) and is used to determine how much a monitor's resolution is scaled relative to the standard 96 DPI (dots per inch) baseline. This scaling is particularly relevant for high-resolution displays, such as 4K or Retina screens, where the system may adjust text and UI elements to appear appropriately sized.

The function takes two parameters: a handle to the monitor (`HMONITOR`) and a pointer to a variable (`DWORD*`) where the scale factor will be stored. The scale factor is returned as a value representing the ratio of the monitor's physical resolution to the standard 96 DPI. For example, a scale factor of 2 indicates that the monitor's resolution is double the standard DPI, meaning text and UI elements will be scaled up by 200%. Common scale factors include 100% (1.0), 125% (1.25), 150% (1.5), and 200% (2.0), though custom values are also possible.

`GetScaleFactorForMonitor` is useful for applications that need to adapt their layout or rendering to accommodate different display resolutions. By querying the scale factor, developers can ensure proper sizing of windows, text, and graphics, improving user experience on high-DPI screens. This function is often paired with `GetMonitorInfo` to retrieve additional details about the monitor, such as its dimensions and work area.

The function is declared in the `windows.h` header file and is part of the `user32.dll` library. It returns a non-zero value on success, indicating the scale factor, or zero if the operation fails, typically due to an invalid monitor handle. Error handling should be implemented to account for such cases.