Clamp a mouse around several 2d objects

It's a little complicated since Unity doesn't have such a function, you have to dive into user32.dll stuff.

This thread details the method:

Constrain Mouse Cusor While Fullscreen (Windows)

 using UnityEngine;
 using System.Collections;
 using System.Runtime.InteropServices;
 
 public class ClipCursorScript : MonoBehaviour
 {
     [DllImport( "user32.dll", CharSet = CharSet.Auto, ExactSpelling = true )]
     [return: MarshalAs( UnmanagedType.Bool )]
     public static extern bool ClipCursor( ref RECT rcClip );
     [DllImport( "user32.dll" )]
     [return: MarshalAs( UnmanagedType.Bool )]
     public static extern bool GetClipCursor( out RECT rcClip );
     [DllImport( "user32.dll" )]
     static extern int GetForegroundWindow( );
     [DllImport("user32.dll")]
     [return: MarshalAs( UnmanagedType.Bool )]
     static extern bool GetWindowRect( int hWnd, ref RECT lpRect );
     
     [StructLayout( LayoutKind.Sequential )]
     
     public struct RECT
     {
         public int Left;
         public int Top;
         public int Right;
         public int Bottom;
         public RECT( int left, int top, int right, int bottom )
         {
             Left = left;
             Top = top;
             Right = right;
             Bottom = bottom;
         }
     }
     
     RECT currentClippingRect;
     RECT originalClippingRect = new RECT( );
     
     void Start()
     {
         currentClippingRect = new RECT(Screen.width / 2 - 10, Screen.height / 2 - 10, Screen.width / 2 + 10, Screen.height / 2 + 10);
         ClipCursor( ref currentClippingRect);
 
     }
     
     void OnApplicationQuit()
     {
         ClipCursor( ref originalClippingRect );
     }
 }

The currentClippingRect is the rect that will constrain the cursor. Note that it will only work in full screen mode, as it uses screen coordinates of the WHOLE screen, not just what Unity would regard as a screen (the window where the game is ran).