directdraw:载入JPGE图象文件到DirectDraw的表面中

Loading JPEGs to DirectDraw Surfaces
载入JPGE图象文件到DirectDraw表面中
by Johnny Wood
译: sea_bug

译者话:这是篇有关使用Intel JPGEs Library文章在翻译同时译者根据自己使用经验对文章进行适当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排列顺序我先决定安排些假设首先我假设你已经了解C/C和如何对代码进行调试我还假设你对DirectDraw有些了解和你拿到了DirectX 7.0库文件并且能够在24bit情况下工作注意:本文章附带原代码EXAMPLE.ZIP中提供转换到16bit和32bit表面操作


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 erested in. What we really want are the IJL.H, IJL15.LIB, and IJL15.DLL files that come with the package. _disibledevent=>
要载入JPGE图象文件首先要Intel网站WebSite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东西我们真正要是IJL.HIJL15.LIB和IJL15.DLL文件旦你拥有了这些文件包含IJL.H头文件到你代码文件中添加IJL15.LIB文件到你工程并且确定IJL15.DLL文件是在有效位置如C:\\Windows\\Sysstem文件夹当然也可以跟我们编译出来程式执行档放置于同文件夹


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的前先准备好我们需要确定我们拥有可工作DirectDraw表面:

LPDIRECTDRAWSURFACE7 Surface = NULL;

We need to also be sure to our display bit depth to 24 bit:
我们还需要设置我们视频模式深度为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图象到我们表面既然我们要使用Intel JPEG Library我们需要建立个连接对象:

IJLERR jerr;
JPEG_CORE_PROPERTIES jcprops;

IJLERR holds information for determining a pass or fail status.
JPEG_CORE_PROPERTIES is our JPEG object. _disibledevent=>
IJLERR保存返回终止或属性信息
JPEG_CORE_PROPERTIES是我们JPEG对象旦我们有这两个对象我们准备对其进行化:

jerr = ijlInit(&jcprops);
(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化JPEG_CORE_PROPERTIES对象我们能检测这个测试我们IJLERR对象是否化属性是否为IJL_OK

At this po, we must decide 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JPEG图象还是从数据缓冲从文件载入所需步骤较少我们将用这思路方法无论如何在文章例子EXAMPLE.ZIP中,我会给出两种可用思路方法我们从文件中载入并转换我们JPEG对象JPG文件成员到个文件名我们当ijlRead可以重新获得文件参数

jcprops.JPGFile = FileName;
jerr = ijlRead(&jcprops, IJL_JFILE_READPARAMS);
(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.
这指定我们JPGE对象文件名我们将根据这个进行载入我们现在必须寻找个转换方式用于JPGE设备和bitmap(BID)因此我们能绑定它到我们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:
我们开始建立个缓冲为保存我们位图数据在这个缓冲建立的后我们必须调整大小以适合个24bit位图:

//Prepare a 24Bit buffer to receive image data
BYTE *buffer24;

//Determine the required size
long szbuff24 = (jcprops.JPGWidth * 24 + 7) / 8 * jcprops.JPGHeight;

//Resize the buffer and check for null
buffer24 = BYTE [szbuff24];
(buffer24 NULL)
//Report memory allocation error

Now we need to fill in the DIB portion of the JPEG object to get ready for the conversion from JPEG to DIB.
现在我们需要为JPEG对象准备好转换到BID部分进行填充

jcprops.DIBWidth = jcprops.JPGWidth;
jcprops.DIBHeight = jcprops.JPGHeight; //Implies a bottom-up DIB.
jcprops.DIBChannels = 3;
jcprops.DIBColor = IJL_BGR;
jcprops.DIBPadBytes = IJL_DIB_PAD_BYTES(jcprops.JPGWidth, 3);
jcprops.DIBBytes = reerpret_cast (buffer24);

Let\'s look at some of these a little closer. The DIBBytes member pos to the buffer that we created. When we retrieve the JPEG data, the information we get will be stored in this buffer. The DIBWidth and DIBHeight members specy the size of the DIB. The DIBColor member species that we want our image data in reverse order Blue Green Red. That\'s the way that DIBs are actually stored. They are also stored upside down. You can flip the retrieved image by negating the DIBHeight member:
让我们看看这些结构DIBBytes成员变量指向个我们已经建立好数据缓冲当我们重新获得JPEG数据这些信息将是我们用于存储缓冲；DIBWidth和DIBHeight成员指定DIB大小；DIBColor成员指定我们要我们位图数据是倒序兰、绿、红那是DIBs实际存储方式他们也是颠倒存放你可以翻转它:

//This is what you should do you find your images are coming out upside down.
jcprops.DIBHeight = - jcprops.JPGHeight;

Before we read in the image, we have to check _disibledevent=>
在我们读数据的前我们还要检测其它东西:JPG颜色空间

//Set the JPG color space ... this will always be somewhat of an
//educated guess at best because JPEG is \"color blind\" (i.e.,
//nothing in the bit stream tells you what color space the data was
//encoded from.
switch(jcprops.JPGChannels)
{


1: jcprops.JPGColor = IJL_G;
;

3: jcprops.JPGColor = IJL_YCBCR;
;

default:
//This catches everything , but no color twist will be
//performed by the IJL.
jcprops.DIBColor = (IJL_COLOR)IJL_OTHER;
jcprops.JPGColor = (IJL_COLOR)IJL_OTHER;
;
}

We are finally ready to retrieve the actual JPEG image. Thanks to Intel\'s JPEG Library - this is a trivial task:
我们准备最终获得JPEG图象数据感谢IntelJPEG库—这是个十分简单任务:

//Read in image from file
jerr = ijlRead(&jcprops, IJL_JFILE_READWHOLEIMAGE);
(jerr != IJL_OK)
//Report read error

This function copies the image information o our buffer. At this po, we were to insert a BITMAPFILEHEADER and a BITMAPINFOHEADER at the front of our buffer, we could dump the buffer to a binary file. This would effectively create a bitmap file saved to disk. However, we instead want to turn our image o a DIB and attach it to a Direct Draw surface. Therefore, we use the Windows API function CreateBitmap to build our DIB:
这个拷贝位图信息到我们缓冲在这个地方如果我们是插入个BITMAPFILEHEADER或个BITMAPINFOHEADER到我们缓冲前面我们可以颠倒缓冲到个 2进制文件中这将在磁盘上建立个有效BMP图象文件无论如何我们插入要旋转我们位图到个DIB中并把它关联到个DirectDraw表面上因此我们使用Windows APICreateBitmap建立我们DIB:

HBITMAP hbm;

//Create the bitmap and get a handle to it
hbm = CreateBitmap (jcprops.JPGWidth, jcprops.JPGHeight, 1, 24, buffer24);
(hbm NULL)
//Report failure to create bitmap

The CreateBitmap function takes the dimmensions of the image, the number of channels, the number of bits per pixel, and the color bit information from our bitmap buffer and creates a bitmap for us. Upon success, we are given a handle to the ly created bitmap.
CreateBitmap任务是为我们创建个位图包括通道数量、像素bit数量、颜色bit信息在成功基础上我们获得个新建立位图句柄

Before we go any further, we need to make sure that we have a Direct Draw surface to copy our bitmap to. Set up the Direct Draw surface description and create the surface:
在我们进入更深层次的前我们需要确认我们有个用于我们位图拷贝DirectDraw表面设置DirectDraw表面结构并且建立表面:

DDSURFACEDESC2 ddsd;

ZeroMemory(&ddsd, (ddsd));
ddsd.dwSize = (ddsd);
ddsd.dwFlags = DDSD_CAPS | DDSD_HEIGHT | DDSD_WIDTH;
ddsd.ddsCaps.dwCaps = DDSCAPS_OFFSCREENPLAIN;
ddsd.dwWidth = jcprops.JPGWidth;
ddsd.dwHeight = jcprops.JPGHeight;

Result = DDObject->CreateSurface(&ddsd, &Surface, NULL);
(Result != DD_OK)
//Report surface creation error

Now, all that is left is to copy our bitmap over to our Direct Draw surface. Fortunately, there is a function provided by Direct Draw that does just that. It can be found in the DDUTILS.CPP file:
现在拷贝我们位图到我们DirectDraw表面上幸运是倘若在DirectDraw正好是个它能建立在DDUTILS.CPP文件里:


DDCopyBitmap(Surface, hbm, 0, 0, 0, 0);

Before we test our image out, let\'s clean up some things that we don\'t need any more:
在我们测试我们位图前让我们清理些东西那是我们不需要:

//We no longer need our image buffer
delete buffer24;

//Release the JPEG object
ijlFree(&jcprops);

Finally, the time has come to take our image for a test drive:
最终我们对我们位图进行测试:



RECT Image;

//Re surface description
ZeroMemory(&ddsd, (ddsd));
ddsd.dwSize = ( ddsd );

//Get the surface description so that we can dynamically
//find the width and height of our surface
Result = Surface->GetSurfaceDesc(&ddsd);
(Result DD_OK)
{
//Coordinates of image size
Image.left = 0;
Image.top = 0;
Image.right = ddsd.dwWidth;
Image.bottom = ddsd.dwHeight;

//Blit image to back buffer
while (true)
{
Result = BackBuffer->BltFast (0, 0, Surface, &Image, DDBLTFAST_WAIT | DDBLTFAST_NOCOLORKEY);
( Result DD_OK ) ;
( Result DDERR_SURFACELOST )
{
Result = RestoreAll;
( Result != DD_OK ) ;
}
( Result != DDERR_WASSTILLDRAWING ) ;
}
}

If everything goes smoothly, you should see your image pop up _disibledevent=>
如果切正常你将要看到你位图显示在屏幕上当你不再需要它你依然要释放你表面或者你在ALT+TAB时候需要对表面进行恢复你按照严格不走就能恢复表面当然你将不需要再此建立表面

Good luck, and have fun with JPEGs!
祝你好运并希望使用JPEGs得开心

Tags:  directdrawerror directdraw不可用 directdraw加速 directdraw

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