How Can C# Applications Accurately Retrieve Windows Display Scaling Factors?

Accessing Windows Display Settings in C# Applications

Windows 7 and later versions offer customizable display settings, allowing users to adjust text size and other visual aspects. Accessing these settings is crucial for many applications to ensure proper functionality.

Retrieving Windows Display Scaling in C#

While C# can access display settings, relying solely on graphics.DpiX and DeviceCap.LOGPIXELSX might not provide accurate scaling factors across all levels.

A More Accurate Scaling Factor Calculation

For precise scaling factor determination, use this method:

1. Import the gdi32.dll library.

2. Define an enumeration for Device Capabilities (DeviceCap).

3. Implement a method to compute the scaling factor:

   • Obtain the Graphics Context (GDI) for the desktop.
   • Use GetDeviceCaps to retrieve the logical and physical screen heights in pixels.
   • Release the GDI handle.
   • Calculate the scaling factor by dividing the physical height by the logical height.

Code Example:

using System;
using System.Drawing;
using System.Runtime.InteropServices;

public class DisplayScaler
{
    [DllImport("gdi32.dll")]
    static extern int GetDeviceCaps(IntPtr hdc, int nIndex);

    public enum DeviceCap
    {
        VERTRES = 10,
        DESKTOPVERTRES = 117
    }

    public float GetScalingFactor()
    {
        using (Graphics g = Graphics.FromHwnd(IntPtr.Zero))
        {
            IntPtr desktop = g.GetHdc();
            int logicalHeight = GetDeviceCaps(desktop, (int)DeviceCap.VERTRES);
            int physicalHeight = GetDeviceCaps(desktop, (int)DeviceCap.DESKTOPVERTRES);
            g.ReleaseHdc(desktop);
            return (float)physicalHeight / logicalHeight;
        }
    }
}

This approach ensures C# applications accurately retrieve the Windows display scaling factor, enabling adjustments based on user display settings.

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