摇杆脚本

using UnityEngine;
using System;

[ExecuteInEditMode]
public class Joystick : MonoBehaviour {

    public enum JoystickAnchor { None, UpperLeft, UpperCenter, UpperRight, MiddleLeft, MiddleCenter, MiddleRight, LowerLeft, LowerCenter, LowerRight };
    public JoystickAnchor joyAnchor = JoystickAnchor.LowerLeft;

    public int guiDepth = 0;
    public Texture2D areaTexture;
    public Texture2D touchTexture;
    public Rect areaRect;
    public Rect touchRect;
    public Vector2 offset;
    public GameObject eventReceiver;
    public string functionName = "OnJoystickChanged";
    public event Action<Vector2> OnJoystickChanged;

    private Vector2 anchorPosition;
    private Vector2 joystickCenter;
    private Vector2 touchPosition;
    private Vector2 last_touchPosition;
    private float areaRadius, areaRadiusSqr, touchRadius, touchRadiusSqr;
    private bool joystickDraging;

    void OnEnable()
    {
        ComputeJoystickAnchor(joyAnchor);
    }

    void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            CheckTouchPosition();
        }
        else if (Input.GetMouseButtonUp(0))
        {
            ResetJoystick();
        }

        if (joystickDraging)
        {
            UpdateJoystick();
        }

        if (null != OnJoystickChanged && last_touchPosition != touchPosition)
        {
            last_touchPosition.Set(touchPosition.x, touchPosition.y);
            OnJoystickChanged(last_touchPosition);
        }

        if (null != eventReceiver && !string.IsNullOrEmpty(functionName) && last_touchPosition != touchPosition)
        {
            last_touchPosition.Set(touchPosition.x, touchPosition.y);
            eventReceiver.SendMessage(functionName, last_touchPosition, SendMessageOptions.DontRequireReceiver);
        }
    }

    void CheckTouchPosition()
    {
        UpdateTouchPosition();
        if (touchPosition.sqrMagnitude <= areaRadiusSqr)
            joystickDraging = true;
    }

    void UpdateTouchPosition()
    {
        touchPosition.x = Input.mousePosition.x;
        touchPosition.y = Screen.height - Input.mousePosition.y;
        touchPosition -= joystickCenter;
    }

    void UpdateJoystick()
    {
        UpdateTouchPosition();
        ComputeJoystickAnchor(joyAnchor);
    }

    void ResetJoystick()
    {
        joystickDraging = false;
        touchPosition = Vector2.zero;
        ComputeJoystickAnchor(joyAnchor);
    }

    void OnGUI()
    {
        GUI.depth = guiDepth;

        if (null != areaTexture)
        {
            GUI.DrawTexture(areaRect, areaTexture, ScaleMode.StretchToFill, true);
        }

        if (null != touchTexture)
        {
            GUI.DrawTexture(touchRect, touchTexture, ScaleMode.StretchToFill, true);
        }
    }

    void ComputeJoystickAnchor(JoystickAnchor anchor)
    {
        // Anchor position
        switch (anchor)
        {
            case JoystickAnchor.UpperLeft:
                anchorPosition = Vector2.zero;
                break;
            case JoystickAnchor.UpperCenter:
                anchorPosition = new Vector2((Screen.width - areaRect.width) / 2, 0);
                break;
            case JoystickAnchor.UpperRight:
                anchorPosition = new Vector2(Screen.width - areaRect.width, 0);
                break;

            case JoystickAnchor.MiddleLeft:
                anchorPosition = new Vector2(0, (Screen.height - areaRect.height) / 2);
                break;
            case JoystickAnchor.MiddleCenter:
                anchorPosition = new Vector2((Screen.width - areaRect.width) / 2, (Screen.height - areaRect.height)/2 );
                break;
            case JoystickAnchor.MiddleRight:
                anchorPosition = new Vector2(Screen.width - areaRect.width, (Screen.height - areaRect.height) / 2);
                break;

            case JoystickAnchor.LowerLeft:
                anchorPosition = new Vector2(0, Screen.height - areaRect.height);
                break;
            case JoystickAnchor.LowerCenter:
                anchorPosition = new Vector2( (Screen.width - areaRect.width)/2, Screen.height - areaRect.height);
                break;
            case JoystickAnchor.LowerRight:
                anchorPosition = new Vector2(Screen.width - areaRect.width, Screen.height - areaRect.height);
                break;

            case JoystickAnchor.None:
                anchorPosition = Vector2.zero;
                break;
        }

        anchorPosition.x += offset.x;
        anchorPosition.y += offset.y;

        if (touchPosition.sqrMagnitude > touchRadiusSqr)
        {
            touchPosition.Normalize();
            touchPosition *= touchRadius;
        }

        //joystick rect
        areaRadius = areaRect.width / 2;
        areaRadiusSqr = areaRadius * areaRadius;
        touchRadius = areaRadius - touchRect.width / 2;
        touchRadiusSqr = touchRadius * touchRadius;

        joystickCenter.x = anchorPosition.x + areaRect.width / 2;
        joystickCenter.y = anchorPosition.y + areaRect.height / 2;

        areaRect.x = anchorPosition.x;
        areaRect.y = anchorPosition.y;

        touchRect.x = joystickCenter.x - touchRect.width / 2 + touchPosition.x;
        touchRect.y = joystickCenter.y - touchRect.height / 2 + touchPosition.y;
        touchRect.x = Mathf.Clamp(touchRect.x, areaRect.x, areaRect.x + areaRect.width - touchRect.width);
        touchRect.y = Mathf.Clamp(touchRect.y, areaRect.y, areaRect.y + areaRect.height - touchRect.height);
    }
}

工程结构

运行效果

附上Demo源文件(360云盘)