在Unity 中要通过代码将一张贴图切割成多张小图，可以使用以下方法：

    /// <summary>
    /// 把一张图片切割成多张使用
    /// </summary>
    /// <param name="texture">原图</param>
    /// <param name="rows">切割的行数</param>
    /// <param name="columns">切割的列数</param>
    /// <returns></returns>
    public List<Texture2D> CutPic(Texture2D texture,int rows,int columns)
    {
        List<Texture2D> texs = new List<Texture2D>();
        int width = texture.width / columns;
        int height = texture.height / rows;
        for (int row = 0; row < rows; row++)
        {
            for (int col = 0; col < columns; col++)
            {
                int x = col * width;
                int y = row * height;
                Rect rect = new Rect(x, y, width, height);
                Texture2D tex = new Texture2D(width, height, TextureFormat.RGBA32, false);
                //Sprite sprite = Sprite.Create(texture, rect, new Vector2(0.5f, 0.5f));
                Color[] pixels = texture.GetPixels(x, y, width, height);
                tex.SetPixels(pixels);
                tex.Apply();
                texs.Add(tex);
            }
        }
        return texs;
    }

 注意：要想成功实现切割，要保证图片是可读的。

使用上面方法我把场景中RawImage里面的贴图切成4块，

List<Texture2D> textures = CutPic((Texture2D)bigImg.texture, 2, 2);

然后再把切出的图分别给到4个新的RawImage，效果如下图。

完成得不错！