c++ how to send Hbitmap over socket

Question

My GetScreen function looks like:

void GetScreen(int clientSocket, const char *filename) {   
         HDC hDC = NULL;
         int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
         int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);
         HWND hDesktopWnd = GetDesktopWindow();
         HDC hDesktopDC = GetDC(hDesktopWnd);
         HDC hCaptureDC = CreateCompatibleDC(hDesktopDC);
         HBITMAP hCaptureBitmap =CreateCompatibleBitmap(hDesktopDC, 
                                 nScreenWidth, nScreenHeight);
         SelectObject(hCaptureDC,hCaptureBitmap); 
         BitBlt(hCaptureDC,0,0,nScreenWidth,nScreenHeight,
                hDesktopDC,0,0,SRCCOPY|CAPTUREBLT); 
         SaveBitmap(clientSocket, "test.bmp",hCaptureBitmap); //here to save the captured image to disk
         **//here to send Hbitmap: send(clientSocket,?,?,Null);**

         ReleaseDC(hDesktopWnd,hDesktopDC);
         DeleteDC(hCaptureDC);
         DeleteObject(hCaptureBitmap);
}

Now I want to send HBITMAP over socket without bitmap saving. I've Googled and have found GetDIBits and SetDIBits but I do not know how I can use it exactly. Can someone help me? Thank you.

now i tried to get BYTE from HBITMAP with this code:

BYTE* getPixArray(HBITMAP hBitmap)
        {
        HDC hdc,hdcMem;

        hdc = GetDC(NULL);
        hdcMem = CreateCompatibleDC(hdc); 

        BITMAPINFO MyBMInfo = {0};
        MyBMInfo.bmiHeader.biSize = sizeof(MyBMInfo.bmiHeader);
        // Get the BITMAPINFO structure from the bitmap
        if(0 == GetDIBits(hdcMem, hBitmap, 0, 0, NULL, &MyBMInfo, DIB_RGB_COLORS))
        {
            cout<<"FAIL\n"<<endl;
        }

        // create the bitmap buffer
        BYTE* lpPixels = new BYTE[MyBMInfo.bmiHeader.biSizeImage];

        MyBMInfo.bmiHeader.biSize = sizeof(MyBMInfo.bmiHeader);
        MyBMInfo.bmiHeader.biBitCount = 32;  
        MyBMInfo.bmiHeader.biCompression = BI_RGB;  
        MyBMInfo.bmiHeader.biHeight = (MyBMInfo.bmiHeader.biHeight < 0) ? (-MyBMInfo.bmiHeader.biHeight) : (MyBMInfo.bmiHeader.biHeight); 

        // get the actual bitmap buffer
        if(0 == GetDIBits(hdc, hBitmap, 0, MyBMInfo.bmiHeader.biHeight, (LPVOID)lpPixels, &MyBMInfo, DIB_RGB_COLORS))
        {
            cout<<"FAIL\n"<<endl;
        }

        return lpPixels;
    }

now in the other side of socket i want to get HBITMAP from BYTE!?! please help me. thx.

Answer 1

Once you have an HBITMAP, call HBITMAPToPixels. Send the width, the height, and the bitsperpixel. Next send the pixels..

On the other end of the socket, read width, read height, read bitsperpixel. Then create a buffer of size: ((width * Bmp.bmBitsPixel + 31) / 32) * 4 * height Read that many bytes into the buffer and call HBITMAPFromPixels

The functions discussed are defined below..

#include <iostream>
#include <stdexcept>
#include <vector>
#include <cstring>
#include <memory>
#include <windows.h>

std::unique_ptr<std::remove_pointer<HBITMAP>::type, std::function<void(HBITMAP)>> HBITMAPFromPixels(const std::vector<std::uint8_t> &Pixels, std::uint32_t width, std::uint32_t height, std::uint16_t BitsPerPixel)
{
    BITMAPINFO Info = {0};
    std::memset(&Info, 0, sizeof(BITMAPINFO));

    Info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    Info.bmiHeader.biWidth = width;
    Info.bmiHeader.biHeight = -height;
    Info.bmiHeader.biPlanes = 1;
    Info.bmiHeader.biBitCount = BitsPerPixel;
    Info.bmiHeader.biCompression = BI_RGB;
    Info.bmiHeader.biSizeImage = ((width * BitsPerPixel + 31) / 32) * 4 * height;

    HBITMAP Result = CreateDIBitmap(GetDC(nullptr), &Info.bmiHeader, CBM_INIT, &Pixels[0], &Info, DIB_RGB_COLORS);
    return std::unique_ptr<std::remove_pointer<HBITMAP>::type, std::function<void(HBITMAP)>>(Result, [&](HBITMAP hBmp){DeleteObject(hBmp);});
}

void HBITMAPToPixels(HBITMAP BitmapHandle, std::vector<std::uint8_t> &Pixels, std::uint32_t &width, std::uint32_t &height, std::uint16_t &BitsPerPixel)
{
    if (BitmapHandle == nullptr)
    {
        throw std::logic_error("Null Pointer Exception. BitmapHandle is Null.");
    }

    Pixels.clear();
    BITMAP Bmp = {0};
    BITMAPINFO Info = {0};
    HDC DC = CreateCompatibleDC(nullptr);
    std::memset(&Info, 0, sizeof(BITMAPINFO));
    HBITMAP OldBitmap = (HBITMAP)SelectObject(DC, BitmapHandle);
    GetObject(BitmapHandle, sizeof(Bmp), &Bmp);

    Info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    Info.bmiHeader.biWidth = width = Bmp.bmWidth;
    Info.bmiHeader.biHeight = height = Bmp.bmHeight;
    Info.bmiHeader.biPlanes = 1;
    Info.bmiHeader.biBitCount = BitsPerPixel = Bmp.bmBitsPixel;
    Info.bmiHeader.biCompression = BI_RGB;
    Info.bmiHeader.biSizeImage = ((width * Bmp.bmBitsPixel + 31) / 32) * 4 * height;

    Pixels.resize(Info.bmiHeader.biSizeImage);
    GetDIBits(DC, BitmapHandle, 0, height, &Pixels[0], &Info, DIB_RGB_COLORS);
    SelectObject(DC, OldBitmap);
    height = height < 0 ? -height : height;
    DeleteDC(DC);
}

Answer 2

Always send the pixel data of the bitmaps (unsigned char *). HBITMAP is just a handle for your bitmap. Also take care of the size issues, if your height, width and bpp are high, u need to think of compressing the pixels data.