unity代码怎么实现鼠标绘制矩形并且被框选的物体变色

实现鼠标绘制矩形的方法可以参考以下代码：

public class DrawRectangle : MonoBehaviour
{
    private Vector2 startPosition;
    private Vector2 endPosition;
    private bool isDrawing;

    private void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            startPosition = Input.mousePosition;
            isDrawing = true;
        }
        else if (Input.GetMouseButtonUp(0))
        {
            isDrawing = false;
            // 在这里获取框选的物体并改变颜色
            ChangeSelectedObjectsColor();
        }

        if (isDrawing)
        {
            endPosition = Input.mousePosition;
        }
    }

    private void OnGUI()
    {
        if (isDrawing)
        {
            Rect rect = new Rect(startPosition.x, Screen.height - startPosition.y, 
                endPosition.x - startPosition.x, -(endPosition.y - startPosition.y));
            GUI.Box(rect, "");
        }
    }

    private void ChangeSelectedObjectsColor()
    {
        // 获取屏幕坐标系下的开始点和结束点
        Vector2 screenStartPosition = Camera.main.ScreenToWorldPoint(startPosition);
        Vector2 screenEndPosition = Camera.main.ScreenToWorldPoint(endPosition);

        // 获取框选区域的边界框
        Bounds selectionBounds = new Bounds((screenStartPosition + screenEndPosition) / 2f, 
            new Vector3(Mathf.Abs(screenEndPosition.x - screenStartPosition.x), 
            Mathf.Abs(screenEndPosition.y - screenStartPosition.y), 1f));

        // 获取所有被框选的物体
        Collider2D[] selectedColliders = Physics2D.OverlapBoxAll(selectionBounds.center, 
            selectionBounds.size, 0f);

        // 改变被框选物体的颜色
        foreach (Collider2D selectedCollider in selectedColliders)
        {
            selectedCollider.GetComponent<Renderer>().material.color = Color.red;
        }
    }
}

上述代码中，首先通过监听鼠标左键按下和抬起的事件来获取框选的起点和终点，然后通过 OnGUI() 函数来绘制矩形框。在鼠标左键抬起的事件中，通过获取框选区域的边界框来获取所有被框选的物体，然后将它们的颜色改变为红色即可。注意，在获取框选区域的边界框时需要将屏幕坐标系转换为世界坐标系。