How can I control the mouse (Move and send mouse click signals) via the keyboard?

So you want to move the mouse, with your keyboard, something like:

 if (left arrow pressed)
    mouse.x -= value;
 else if (right arrow pressed)
    mouse.x += value;
 else if etc

Last time I tried and searched how would I do this, how would I set the mouse cursor coordinates, I failed to find a Unity-way of doing this. Since, setting the system mouse coords, needs actual communication to the operating system, and since each operating system does it in its own way, there isn't one unified way of doing this. But I don't know why didn't Unity do something like:

 public void SetMouse(float x, float y)
 {
     if (OS is Windows)
       doItOne();
     else if (OS is Mac)
       doItTwo();
     else if etc
 }

And then just provide us a common interface we could deal with, so we don't have to worry about which OS we're dealing with, it takes care of it.

ANYWAY, if you're on Windows, you could use some WindowsAPIs to set the coords, like seen in my inventory video (6:30) where I locked the mouse in the bag area.

To get the mouse, you could use GetCursorPos, to set it, SetCursorPos.

First:

 using System.Runtime.InteropServices;

Then you need to import the functions:

 [DllImport("user32.dll")]
 public static extern bool SetCursorPos(int X, int Y);
 [DllImport("user32.dll")]
 public static extern bool GetCursorPos(out Point pos);

Usage:

First, you need to create a Point struct, see. Then you could:

 Point cursorPos = new Point();
 GetCursorPos(out cursorPos);

And:

 SetCursorPos(x, y);

It's good to note that the 0,0 point of the screen for Windows is the top left when you're working with Get/SetCursor. MSDN

EDIT: To send a mouse click from a keyboard button, first go to this link and copy-paste the code in the SECOND answer somewhere (exclude anything you don't need/already have)

Then, to use it:

 public class Test : MonoBehaviour
 {
     void OnGUI()
     {
         if (GUI.Button(new Rect(10, 10, 100, 100), "BUTTON"))
             Debug.Log("clicked button");
     }
     void Update()
     {
         if (Input.GetKeyDown(KeyCode.Space))
             MouseOperations.MouseEvent(MouseOperations.MouseEventFlags.LeftUp | MouseOperations.MouseEventFlags.LeftDown);
     }
 }

This will send out a LeftDown and LeftUp signals. If you just do a LeftDown, it's like holding the left mouse button down, so you won't get a complete click.

Test this code out, attach it to some gameObject, place your mouse on the button, and when you press "Space" it will send a left click as if you clicked on the button, cool huh? :D

 if (OS is Windows)
     doItOne();
 else if (OS is $$anonymous$$ac)
     doItTwo();
 else if etc

 #if UNITY_STANDALONE_WIN
     doItOne();
 #endif
 #if UNITY_STANDALONE_OSX
     doItTwo();
 #endif