载入JPGE图象文件到DirectDraw的表面中

　　译者的话：这是一篇关于使用Intel JPGEs Library的文章，在翻译的同时，译者根据自己的使用经验对文章进行适当的添减章节，希望适合各位读者。
　　
　　In order to keep the size of this article down, I've decided to make a few assumptions. First of all, I assume that you already know C/C++ and how to troubleshoot and debug code. I also assume that you are somewhat familiar with DirectDraw and that you have as a minimum the DirectX 7.0 libraries and the ability to work in 24 bit. Note: the source code in EXAMPLE.ZIP available at the end of this article provides conversions to 16bit and 32bit surfaces.
　　为了保持这篇文章内的排列顺序，我先决定安排一些假设。首先，我假设你已经了解C/C++与如何对代码进行调试。我还假设你对DirectDraw有些了解与你拿到了DirectX 7.0的库文件，并且能够在24bit的情况下工作。注意：本文章附带的原代码EXAMPLE.ZIP中提供转换到16bit和32bit表面的操作。
　　
　　The first step to loading JPEGs is to download the Intel JPEG Library from Intel's website. The Library is loaded with documentation and examples, all of which we're really not interested in. What we really want are the IJL.H, IJL15.LIB, and IJL15.DLL files that come with the package. Once you have those files, include the IJL.H header to
　　your source file, add the IJL15.LIB file to your project, and make sure the IJL15.DLL is in a valid location such as the C:\WINDOWS\SYSTEM folder.
　　要载入JPGE图象文件首先要Intel的网站上去下载Intel JPEG Library，这个库包含了开发文档和例程，以及你不感兴趣的东西。我们真正要的是IJL.H，IJL15.LIB，和IJL15.DLL文件。一旦你拥有了这些文件，包含IJL.H头文件到你的代码文件中，添加IJL15.LIB文件到你的工程，并且确定IJL15.DLL文件是在有效的位置，如C:\Windows\Sysstem文件夹，当然，也可以跟我们编译出来的程式执行档放置于同一文件夹。
　　
　　There are a few more things we need to do before beginning. We need to make sure that we have a Direct Draw Surface to work with:
　　有些东西需要我们在开始之前先准备好，我们需要确定我们拥有可工作的DirectDraw表面：
　　
　　LPDIRECTDRAWSURFACE7 Surface = NULL;
　　
　　We need to also be sure to set our display bit depth to 24 bit:
　　我们还需要设置我们的视频模式，深度为24bit：
　　
　　DDObject->SetDisplayMode(640, 480, 24, 0, 0);
　　
　　We're now ready to load a JPEG to our surface. Since we're using the Intel JPEG Library, we need to create a couple of objects:
　　我们现在准备载入JPEG图象到我们的表面，既然我们要使用Intel JPEG Library，我们需要建立一个连接对象：
　　
　　IJLERR jerr;
　　JPEG_CORE_PROPERTIES jcprops;
　　
　　IJLERR holds return information for determining a pass or fail status.
　　JPEG_CORE_PROPERTIES is our JPEG object. Once we have these two objects, we are ready to initialize them:
　　IJLERR保存返回的终止或错误属性信息。
　　JPEG_CORE_PROPERTIES是我们的JPEG对象，一旦我们有这两个对象，我们准备对其进行初始化：
　　
　　jerr = ijlInit(&jcprops);
　　if (jerr != IJL_OK)
　　//report initialization error
　　
　　The ijlInit function call initializes the JPEG_CORE_PROPERTIES object. We can check the status of this function call by testing whether or not our IJLERR object was initialized with the value IJL_OK.
　　ijlInit函数调用初始化JPEG_CORE_PROPERTIES对象，我们能检测这个函数调用测试我们的IJLERR对象是否初始化属性是否为IJL_OK。
　　
　　At this point, we must decide if we are going to load our JPEG image from a file or from a buffer. Because loading from a file takes fewer steps, we will do that here. However, I give an example of loading from both in the EXAMPLE.ZIP file available at the end of this article. We load from a file by changing our JPEG object's JPGFile member to a file name. We then call ijlRead to retrieve the file parameters.
　　在这点，我们必须决定我们是从文件载入我们的JPEG图象，还是从数据缓冲。因为从文件载入所需的步骤较少，我们将用这方法。无论如何，在文章的例子EXAMPLE.ZIP中,我会给出两种可用的的方法。我们从文件中载入并转换我们的JPEG对象的JPG文件成员到一个文件名，我们当调用ijlRead函数可以重新获得文件参数。
　　
　　jcprops.JPGFile = FileName;
　　jerr = ijlRead(&jcprops, IJL_JFILE_READPARAMS);
　　if (jerr != IJL_OK)
　　//report read error
　　
　　This initial read fills our JPEG object with information about the file we are going to load. What we must now do is find a way of converting the JPEG to a device independent bitmap (DIB) so that we can attach it to our Direct Draw surface.
　　这初始指定我们的JPGE对象的文件名，我们将根据这个进行载入。我们现在必须寻找一个转换的方式用于JPGE设备与bitmap(BID)，因此我们能绑定它到我们的DirectDraw表面。
　　
　　We start by creating a buffer to hold our image data. After the buffer is created, we must resize it to fit a 24Bit image:
　　我们开始建立一个缓冲为保存我们的位图数据，在这个缓冲建立之后，我们必须调整大小以适合一个24bit的位图：
　　
　　//Prepare a 24Bit buffer to receive image data
　　BYTE *buffer24;
　　
　　//Determine the required s