IStream，位图，CBitmap在哪里复制图像数据? [英] IStream, Bitmap, CBitmap where is image data duplicated?

问题描述

我有一个指向数据块的指针，它恰好是从jpeg图像文件读取的二进制数据.我为其创建IStream，并从函数中的流中创建位图，如下所示:

Hi,

I have a pointer to a data block which happen to be binary data read from jpeg image file. I create IStream for it, and create bitmap from the stream in my function as following:

.....
IStream* pStream;
DWORD dwresult = CreateStreamOnHGlobal(NULL, TRUE, &pStream);
pStream->Write(pData, (ULONG)nSize, NULL);

// Create bitmap
Bitmap* pBitmap;
pBitmap = Bitmap::FromStream(pStream);

HBITMAP hBitmap = NULL;
pBitmap->GetHBITMAP(Color(0,0,0),&hBitmap);

CBitmap cbitmap;
cbitmap.Attach(hBitmap);

// imgLst is a CImageList 
imgList.Add(&cbitmap, RGB(0,0,0));
....

问题是图像数据是否在此函数中的某处重复?
(创建IStream时，创建Bitmap对象时，添加到图像列表时)我想确保没有内存泄漏或过早释放.

在此先感谢

Quy

Question is that whether the image data is duplicate somewhere in this function?
(when create IStream, when create Bitmap object, when add to image list) I want to make sure there is no mem leak or premature release.

Thanks in advance

Quy

推荐答案

嗨Quy，

Gdiplus::Bitmap对象本身不会产生新数据，它只是相关编解码器和Gdiplus::Image数据(您的IStream)的连接器.

成功调用pBitmap->GetHBITMAP(Color(0,0,0),&hBitmap);时(从IStream中)读取Gdiplus::Image数据，并由Gdi32.dll创建Windows位图对象.它返回HBITMAP.

此时，您可以关闭IStream并删除HGLOBAL.

调用imgList.Add(&cbitmap, RGB(0,0,0));时，ImageList_Add函数将位图复制到内部数据结构中，并且必须在HBITMAP上调用::DeleteObject().
就您而言，这将在您的cbitmap对象超出范围时发生.

欢呼声，
AR

Hi Quy,

The Gdiplus::Bitmap object by itself produces no new data, it is just a connector to the relevant codec and the Gdiplus::Image data (your IStream).

When you succesfully call pBitmap->GetHBITMAP(Color(0,0,0),&hBitmap); the Gdiplus::Image data are read (from your IStream) and a Windows bitmap object is created by Gdi32.dll; it''s HBITMAP is returned.

At that moment you may close the IStream and delete the HGLOBAL.

When you call imgList.Add(&cbitmap, RGB(0,0,0)); the ImageList_Add function copies the bitmap to an internal data structure, and you must call ::DeleteObject() on the HBITMAP.
In your case this will happen when your cbitmap object gets out of scope.

cheers,
AR

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