Web优化之雪碧图—动态生成雪碧图读凡客产品页所想

从这张图片我们可以看到.SpriteWashings这个样式的背景图是通过joinimages.ashx动态生成，这个想法很好，但是没有生成样式。所以它的html使用了style="background-position: 0px -80px"这个来定位，个人认为这种方式不好，应该通过添加class 来定位，这就需要生成雪碧图的时候要生成相应的样式。

生成雪碧图的原理很简单：根据多个图片地址生成对应的Bitmap，在把这些Bitmap画到一个Bitmap上。

其核心代码如下：

    private static bool GenerateSprite(ImageSettings settings, int x, int y, List<Bitmap> images, StringBuilder cssCompatOutput)
        {
            if (settings.TileInYAxis)
            {
                y += images.Count;
            }
            else
            {
                x += images.Count;
            }

            using (Bitmap sprite = new Bitmap(x, y))
            {
                using (Graphics drawingSurface = Graphics.FromImage(sprite))
                {

                    drawingSurface.Clear(settings.BackgroundColor);

                    int xOffset = 0;
                    int yOffset = 0;
                    foreach (Bitmap image in images)
                    {
                        drawingSurface.DrawImage(image, new Rectangle(xOffset, yOffset, image.Width, image.Height));
                        if (image.Tag != null)
                            GenerateCss(xOffset, yOffset, image, cssCompatOutput, settings);

                        if (settings.TileInYAxis)
                        {
                            yOffset += image.Height + 1;
                        }
                        else
                        {
                            xOffset += image.Width + 1;
                        }
                    }

                    try
                    {
                        using (EncoderParameters spriteEncoderParameters = new EncoderParameters(1))
                        {
                            spriteEncoderParameters.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, settings.Quality);

                            sprite.Save(Path.Combine(settings.SpritePath, GenerateSpriteFileName(settings.SpriteName, settings.Format)), GetEncoderInfo(settings.Format), spriteEncoderParameters);
                        }
                        return true;
                    }
                    catch (Exception ex1)
                    {

                        try
                        {

                            sprite.Save(Path.Combine(settings.SpritePath, GenerateSpriteFileName(settings.SpriteName, settings.Format)));
                            return true;
                        }
                        catch (Exception ex2)
                        {
                            // sprite.Save( Path.Combine(settings.SpritePath, GenerateSpriteFileName(settings.SpriteName, "png")));
                            return false;
                        }
                    }

                }

            }

        }

自己做了一个简单的demo，代码结构如下：

SpriteImage是制作雪碧图的核心代码封装成dll，SpriteImageCreate是一个form工具。

运行效果如下：

看到效果了吧，我们的工具要求生成雪碧图同时也生成css。

我们来看看web的应用吧：

 public ActionResult Index()
        {
            string basedirectory = Path.Combine(this.Request.PhysicalApplicationPath, "Content");
            FileInfo[] files = new DirectoryInfo(Path.Combine(basedirectory, "Images")).GetFiles();
            List<string> filesPath = files.Select(x => x.FullName).ToList();
            ViewData.Add("Sprites", filesPath);
            return View(ViewData);
        }
        [ChildActionOnly]
        public ActionResult Sprite(List<string> images)
        {
            if (images == null || images.Count < 1)
                return View();
            string[] filenames = images.Select(x =>
            {
                int startindex = x.LastIndexOf("\\");
                int endindex = x.LastIndexOf(".");
                return x = x.Substring(startindex + 1, endindex - startindex - 1);
            }).ToArray();

            string spritname = string.Join("", filenames).GetHashCode().ToString();
            string basedirectory = Path.Combine(this.Request.PhysicalApplicationPath, "Content/Sprites");
            string cssFile = Path.Combine(basedirectory, spritname + ".css");
            int index = this.Request.Url.OriginalString.LastIndexOf(this.Request.Url.LocalPath);
            string prfx = this.Request.Url.OriginalString.Substring(0, index);

            if (!System.IO.File.Exists(cssFile))
            {
                ImageSettings setting = new ImageSettings(spritname, basedirectory)
                {
                    CssSpriteUrl = prfx + "/Content/Sprites/",
                    TileInYAxis = false
                };
                StringBuilder sb = new StringBuilder();
                var ret = ImageOptimizations.Optimizations(setting, sb, images);
                if (ret)
                {
                    using (StreamWriter sw = new StreamWriter(cssFile, false, Encoding.UTF8))
                    {
                        sw.Write(sb.ToString());
                    }
                }
            }

            if (System.IO.File.Exists(cssFile))
            {
                string retFormat = " <link type=\"text/css\" rel=\"Stylesheet\" href=\"{0}\" />";
                string url = prfx + "/Content/Sprites/" + spritname + ".css";
                return Content(string.Format(retFormat, url));
            }
            return View();
        }

其中Index的目的是模拟一个动态的图片地址数据，在看看你我们view的代码：

@{
    ViewBag.Title = "Home Page";
    var files = ViewData["Sprites"] as List<string>;
}
@section HeadSection{
    @{ Html.RenderAction("Sprite", "Home", new { images = files });}
}
<div>
    @{
        foreach (var item in files)
        {
            int index = item.LastIndexOf("\\");
            string subname = item.Substring(index + 1);
            subname = subname.Replace(".", "_");
            
        <div class="@subname"  style="float:left " >
        </div>
        }
    }
</div>