fix: Ensure fractional DPI is avoided in HW GTK renderer

src/Uno.UI.Runtime.Skia.Gtk/Extensions/GtkDisplayInformationExtension.cs

@@ -55,7 +55,7 @@ public float LogicalDpi
 				var nativeWindow = window.Window;
 				if (nativeWindow is not null)
 				{
-					_dpi = _dpiHelper.GetNativeDpi();
+					_dpi = GetNativeDpi();
 				}
 			}
 
@@ -72,7 +72,24 @@ public float LogicalDpi
 
 	private void OnDpiChanged(object? sender, EventArgs args)
 	{
-		_dpi = _dpiHelper.GetNativeDpi();
+		_dpi = GetNativeDpi();
 		_displayInformation.NotifyDpiChanged();
 	}
+
+	private float GetNativeDpi()
+	{
+		var dpi = _dpiHelper.GetNativeDpi();
+
+		if (GtkHost.Current?.RenderSurfaceType == RenderSurfaceType.Software)
+		{
+			// Software rendering is not affected by fractional DPI.
+			return dpi;
+		}
+
+		// We need to make sure that in case of fractional DPI, we use the nearest whole DPI instead,
+		// otherwise we get GuardBand related rendering issues.
+		var fractionalDpi = dpi / DisplayInformation.BaseDpi;
+		var wholeDpi = Math.Max(1.0, float.Floor(fractionalDpi));
+		return wholeDpi * DisplayInformation.BaseDpi;
+	}
 }