make it work for just one screen

Program.cs

@@ -1,4 +1,6 @@
-using Svg;
+#define SHOW_ON_ONE_SCREEN
+
+using Svg;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Text.Json;
@@ -6,11 +8,32 @@ using System.Text.Json;
 namespace McsrGraphImageDownloader;
 
 internal class Program {
+#if SHOW_ON_ONE_SCREEN
+    private const int screenToShowItOn = 0; // must be >= 0 and < amount_of_screens, will be clamped if necessary
+
+    [ComImport]
+    [Guid("B92B56A9-8B55-4E14-9A89-0199BBB6F93B")]
+    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+    private interface IDesktopWallpaper {
+        void SetWallpaper([MarshalAs(UnmanagedType.LPWStr)] string monitorID, [MarshalAs(UnmanagedType.LPWStr)] string wallpaper);
+
+        [return: MarshalAs(UnmanagedType.LPWStr)]
+        string GetWallpaper([MarshalAs(UnmanagedType.LPWStr)] string monitorID);
+
+        void GetMonitorDevicePathAt(uint monitorIndex, [MarshalAs(UnmanagedType.LPWStr)] out string monitorID);
+
+        uint GetMonitorDevicePathCount();
+
+        // Remaining methods omitted since not needed
+    }
+#endif
+
     [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
     public static extern int SystemParametersInfo(int uAction, int uParam, string lpvParam, int fuWinIni);
-    public const int SPI_SETDESKWALLPAPER = 20;
+    public const int SPI_SETDESKWALLPAPER = 0x14;
     public const int SPIF_UPDATEINIFILE = 1;
     public const int SPIF_SENDCHANGE = 2;
+
     private const string outputFilename = "mcsrChart.png";
 
     private static async Task Main(string[] args) {
@@ -22,8 +45,25 @@ internal class Program {
             using (var bitmap = svg.Draw(1920, 1080)) {
                 bitmap.Save(outputFilename);
             }
-            SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, Path.GetFullPath(outputFilename), SPIF_UPDATEINIFILE | SPIF_SENDCHANGE);
 
+#if SHOW_ON_ONE_SCREEN
+            Type type = Type.GetTypeFromCLSID(new Guid("C2CF3110-460E-4FC1-B9D0-8A1C0C9CC4BD"))!;
+
+            var wallpaper = (IDesktopWallpaper)Activator.CreateInstance(type)!;
+
+            uint monitorCount = wallpaper.GetMonitorDevicePathCount();
+
+            Console.WriteLine($"Monitor count: {monitorCount}");
+            var monitorIndex = Math.Clamp(screenToShowItOn, 0, monitorCount - 1);
+
+            wallpaper.GetMonitorDevicePathAt(monitorIndex, out string? monitorId);
+
+            wallpaper.SetWallpaper(monitorId, Path.GetFullPath(outputFilename));
+
+            Console.WriteLine($"Wallpaper set for monitor {monitorIndex} only.");
+#else
+            SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, Path.GetFullPath(outputFilename), SPIF_UPDATEINIFILE | SPIF_SENDCHANGE);
+#endif
             await Task.Delay(TimeSpan.FromMinutes(15));
         }
     }