[MFC/C++]Sending CBitmap's bits over socket, and re-construct it on receiver side - c++

Question

I am new with MFC and try to learn it with a project of MFC dialog base on VS2008. Here are the archivements I have done:
First, I have managed to display a list of pictures from a folder to a Listbox Control. After that, I also handled the click event on each line of the listbox to load and show the picture to the Picture Control(type Bitmap) on the right side. You can see the image below for easy understanding: Please click here for the image of my MFC dialog
Here is the code. Note m_ListCtrl and static_picture are variables of the listbox and the picture control:
void CMyClientDlg::OnLbnSelchangeList1(){
CString imagePath;
m_ListCtrl.GetText(m_ListCtrl.GetCurSel(),imagePath);
CImage picture;
picture.Load(imagePath);
if (!picture.IsNull())
{
float screenWidth = 200, screenHeight = 200;
float imageWidth = picture.GetWidth();
float imageHeight = picture.GetHeight();
//scaling:
float pictureRatio = imageWidth/ imageHeight;
float newImageWidth;
float newImageHeight;
int aligmentX = 0;
int aligmentY = 0;
if (pictureRatio <= 1)
{
newImageWidth = imageWidth*(screenHeight/imageHeight);
newImageHeight = screenHeight;
aligmentX = (screenWidth-newImageWidth)/2;
}
else
{
newImageWidth = screenWidth;
newImageHeight = imageHeight*(screenWidth/imageWidth);
aligmentY = (screenHeight - newImageHeight)/2;
}
//end scaling.
CDC *screenDC = GetDC();
CDC mDC;
mDC.CreateCompatibleDC(screenDC);
CBitmap bitMap;
bitMap.CreateCompatibleBitmap(screenDC, screenWidth, screenHeight);
CBitmap *pob = mDC.SelectObject(&bitMap);
mDC.SetStretchBltMode(HALFTONE);
picture.StretchBlt(mDC.m_hDC, aligmentX, aligmentY, newImageWidth, newImageHeight, 0, 0, imageWidth, imageHeight, SRCCOPY);
mDC.SelectObject(pob);
/*.......code to convert bitmap to BYTE* ........*/
/*.......code to send BYTE* over socket........*/
//display the bit map
static_picture.SetBitmap((HBITMAP)bitMap.Detach());
//clean up
ReleaseDC(screenDC);
}
}
So now I would like to advance one more step, and tried to work with socket... and yes, I successfully sent and received simple char* or CString over socket.
What I want to do is: instead showing the picture on this dialog, it shows the image on the other dialog(server).
Somehow I learned that there are 2 funtions that sound work: SetBitmapBits() and GetBitmapBits() (I honestly just read it on some source and have no idead if they suitable for my goal here).
So, I added this piece of code to turn the above bitmap into array of BYTE bmpBuffer:
BITMAP bmpProperties;
bitMap.GetBitmap(&bmpProperties);
int bmpDemension = bmpProperties.bmWidthBytes*bmpProperties.bmHeight;
BYTE* bmpBuffer=(BYTE*)GlobalAlloc(GPTR, bmpDemension);
bitMap.GetBitmapBits(bmpDemension,bmpBuffer);
Then send that array over socket:
UpdateData(TRUE);
char *socketBuffer = reinterpret_cast<char*>(bmpBuffer);
send(m_ClientSocket, socketBuffer, sizeof(socketBuffer), 0);
//clean up after send
GlobalFree((HGLOBAL)bmpBuffer);
On the other dialog. Note: I have hardcoded the demension of the bitmap to 160000, just to simplify the problem:
void CMyServer2Dlg::OnReceive(){
char *socketBuffer = new char [1025];
int iLen;
iLen = recv(m_sConnected, socketBuffer, 1025, NULL);
if(iLen==SOCKET_ERROR)
{
AfxMessageBox("Could not Receive");
}
else
{
BYTE* bmpBuffer = reinterpret_cast<BYTE*>(socketBuffer);
//re-construct the bitmap
CBitmap clone;
CDC *screenDC = GetDC();
CDC mDC;
mDC.CreateCompatibleDC(screenDC);
clone.CreateCompatibleBitmap(screenDC, 200, 200);
clone.SetBitmapBits(160000,bmpBuffer);
//Picture control(type bitmap) has variable "static_picture"
static_picture.SetBitmap((HBITMAP)clone.Detach());
UpdateData(FALSE);
ReleaseDC(screenDC);
GlobalFree((HGLOBAL)bmpBuffer);
}
delete socketBuffer;
And, it just doesn't work... Please tell me where did I mess it up? And sorry for the long post.....

Answer 1

I think the most possible reason is that your receiver doesn't get all data of the picture. I suggest you put a size of the bitmap into the package while sending it, for receiver to get correct size.
Here are some sample code. Be aware they are just for showing the idea, you may need some debugging to make sure they work.
step 1: Pack the size of bitmap. I suppose here the size is less than 64K, so a int is used. If size may be bigger than 64k, you may want to use INT64.
int bmpDemension = bmpProperties.bmWidthBytes*bmpProperties.bmHeight;
int bufferSize = bmpDemension + sizeof(int);
BYTE* bmpBuffer=(BYTE*)GlobalAlloc(GPTR, bufferSize );
bitMap.GetBitmapBits(bmpDemension,bmpBuffer + sizeof(int));
memcpy(bmpBuffer, &bmpDemension, sizeof(int)); // put the size into the head of package.
step 2: Send it out
Be aware, I use bufferSize here, because sizeof(bmpBuffer) returns the pointer size, which is 4, not the space size.
UpdateData(TRUE);
char *socketBuffer = reinterpret_cast<char*>(bmpBuffer);
send(m_ClientSocket, socketBuffer, bufferSize , 0);
//clean up after send
GlobalFree((HGLOBAL)bmpBuffer);
At the receiver side:
First, you read the size of the bitmap, then do receive according to the size of data.
void CMyServer2Dlg::OnReceive(){
char socketBuffer[1025];
int iLen;
iLen = recv(m_sConnected, socketBuffer, sizeof(int), NULL); //read the bigmap size
if(iLen==SOCKET_ERROR)
{
AfxMessageBox("Could not Receive");
}
else
{
int dimension = *((int *) socketBuffer);
char * bitmapBuffer = new char[dimension];
int readSize = dimension;
char * pBuffer = bitmapBuffer;
while (readSize > 0)
{
int sizeToRead = readSize > sizeof(socketBuffer) ? sizeof(socketBuffer) : readSize;
iLen = recv(m_sConnected, socketBuffer, sizeToRead , NULL);
memcpy(pBuffer, socketBuffer, iLen);
pBuffer += iLen;
readSize -= iLen;
}
// when the loop done, you shall have all data in bitmapBuffer.
....
// I leave the remaining code to you.
Again, these code is just to demo the idea.