所以对于你y坐标，屏幕空间和世界空间在不同的屏幕上是不同的。把你的y改为Screen. height-mousePosition. y。这会帮你解决这个问题

为了防止有人像我一样纠结于此，这里是解决方案，它似乎可以正常工作。该解决方案使用@Alex的初始代码和@Technivorous的调整。

using UnityEngine;
using System.Collections;
using System;

public class MouseDragSelection : MonoBehaviour
{

    private Rect position = new Rect(193, 148, 249 - 193, 148 - 104);
    public Color color = Color.green;
    private Vector3[] mousePositions = new Vector3[2];
    private bool draggingMouse = false;
    private bool drawRect = false;
    public float timer = 1.2f;

    void OnGUI()
    {
        if (drawRect)
        {
            DrawRectangle(position, 1, color);
        }
    }

    void DrawRectangle(Rect area, int frameWidth, Color color)
    {
        //Create a one pixel texture with the right color
        var texture = new Texture2D(1, 1);
        texture.SetPixel(0, 0, color);
        texture.Apply();

        Rect lineArea = area;
        lineArea.height = frameWidth; //Top line
        GUI.DrawTexture(lineArea, texture);
        lineArea.y = area.yMax - frameWidth; //Bottom
        GUI.DrawTexture(lineArea, texture);
        lineArea = area;
        lineArea.width = frameWidth; //Left
        GUI.DrawTexture(lineArea, texture);
        lineArea.x = area.xMax - frameWidth;//Right
        GUI.DrawTexture(lineArea, texture);
    }

    void reset()
    {
        drawRect = false;
        mousePositions[0] = new Vector3();
        mousePositions[1] = new Vector3();
        timer = 1.2f;
        draggingMouse = false;
    }
    private void Update()
    {
        if (drawRect)
        {
            if (timer > 0.1)
            {
                timer -= 1 * Time.deltaTime;
            }
            else
            {
                reset();
            }
        }
        if (Input.GetMouseButtonDown(0))
        {
            if (!draggingMouse)
            {
                mousePositions[0] = Input.mousePosition;
                print("x start:" + mousePositions[0].x);
                print("y start:" + mousePositions[0].y);
            }
            draggingMouse = true;
        }
        if (Input.GetMouseButtonUp(0))
        {
            if (draggingMouse)
            {
                mousePositions[1] = Input.mousePosition;
                float width = Math.Abs(mousePositions[1].x - mousePositions[0].x);
                float height = Math.Abs(mousePositions[1].y - mousePositions[0].y);
                float x = mousePositions[0].x;
                float y = Screen.height - mousePositions[0].y;
                // print("width:" + width);
                // print("height:" + height);
                print("x end:" + mousePositions[1].x);
                print("y end:" + mousePositions[1].y);
                if (mousePositions[0].x < mousePositions[1].x && mousePositions[0].y < mousePositions[1].y)
                {
                    print("x1 < x2, y1 < y2");
                    position = new Rect(x, y, width, -height);
                }
                else if (mousePositions[0].x > mousePositions[1].x && mousePositions[0].y < mousePositions[1].y)
                {
                    print("x1 > x2, y1 < y2");
                    position = new Rect(x, y, -width, -height);
                }
                else if (mousePositions[0].x < mousePositions[1].x && mousePositions[0].y > mousePositions[1].y)
                {
                    print("x1 < x2, y1 > y2");
                    position = new Rect(x, y, width, height);
                } else
                {
                    print("x1 > x2, y1 > y2");
                    position = new Rect(x, y, -width, height);
                }
                // print("Got last mouse position!");
                drawRect = true;
            }
        }
    }
}

关键问题是Technivorous建议的Screen.height-mousePosition.y，但是这个问题可以更简洁地解决：

public class DrawSelect : MonoBehaviour
{
    Texture2D selectTexture;

    Vector3 boxOrigin;
    Vector3 boxEnd;

    bool drawing;

    private void Start() {
        selectTexture = new Texture2D(1, 1);
        selectTexture.SetPixel(0, 0, UnityEngine.Color.white);
        selectTexture.Apply();
    }

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Mouse0)) {
            boxOrigin = Input.mousePosition;
            drawing = true;
        }

        if (drawing) {
            boxEnd = Input.mousePosition;
        }

        if(Input.GetKeyUp(KeyCode.Mouse0)) {
            drawing = false;
        }
    }

    void OnGUI() {
        if (drawing) {
            Rect area = new Rect(boxOrigin.x, Screen.height - boxOrigin.y, boxEnd.x - boxOrigin.x, boxOrigin.y - boxEnd.y);
            
            Rect lineArea = area;
            lineArea.height = 1; //Top line
            GUI.DrawTexture(lineArea, selectTexture);
            lineArea.y = area.yMax - 1; //Bottom
            GUI.DrawTexture(lineArea, selectTexture);
            lineArea = area;
            lineArea.width = 1; //Left
            GUI.DrawTexture(lineArea, selectTexture);
            lineArea.x = area.xMax - 1;//Right
            GUI.DrawTexture(lineArea, selectTexture);
        }
    }

}