C++ BITMAP to C# Bitmap

Question

I am trying to create a simple screenshare program, with a C++ server, and a C# client. I am currently trying to achieve this by sending the buffer you get from BitBlt, and sending that over the net. This all seems to go alright, but when I try to read the buffer in my C# client, the image looks messed up. An example: enter image description here

The code I'm using to get the buffer on the C++ end (Found this code somewhere):

void ScreenCap()
{
    HDC hdc = GetDC(NULL), hdcMem = CreateCompatibleDC (hdc);
    HBITMAP hBitmap = CreateCompatibleBitmap(hdc, ScreenX, ScreenY);
    BITMAPINFOHEADER bmi = {0};
    bmi.biSize = sizeof(BITMAPINFOHEADER);
    bmi.biPlanes = 1;
    bmi.biBitCount = 24;
    bmi.biWidth = ScreenX;
    bmi.biHeight = -ScreenY;
    bmi.biCompression = BI_RGB;
    SelectObject(hdcMem, hBitmap);
    BitBlt(hdcMem, 0, 0, ScreenX, ScreenY, hdc, 0, 0, SRCCOPY);
    int res = GetDIBits(hdc, hBitmap, 0, ScreenY, ScreenData, (BITMAPINFO*)&bmi, DIB_RGB_COLORS);
    DeleteObject(hBitmap);
    DeleteDC(hdcMem);
    ReleaseDC(NULL, hdc);
}

Code I'm using to display the image on the C# end:

char[] buffer = packet.getData();
Bitmap bitmap = new Bitmap(clientWidth, clientHeight);
BitmapData bData = bitmap.LockBits(new Rectangle(0, 0, clientWidth, clientHeight), ImageLockMode.ReadWrite, bitmap.PixelFormat);
Marshal.Copy(Helper.toByteArray(buffer), 0, bData.Scan0, buffer.Length);
bitmap.UnlockBits(bData);

pictureBox1.Invoke(new Action(() =>
{
    pictureBox1.Image = bitmap;
}));

I honestly have no idea whats going on.

EDIT

Some additional information:

Screen Width: 1366 (Both in client and the server)

Screen Height: 768 (Also both the same, in client and server)

For the buffer size, I am simply just using width * height * 3, in this case its 3147264

Out of the blue: You are reading your bitmap in C++ as 24 bit RGB but in C# you are using the default pixel format which is 32bpp. Could you post the values of buffer.Length, clientWidth and clientHeight? And also there might be some confusion: sizeof(char) in C++ is guaranteed to be 1, in .NEt its usually 2. — Muepe
– Muepe, Commented Apr 1, 2014 at 20:52
You can take screenshot from C# code. If that's an option, see this — vulcan raven
– vulcan raven, Commented Apr 1, 2014 at 20:53
Yes Muepe, give me one second. I'll add them to the question. EDIT Added them to the question — user2073973
– user2073973, Commented Apr 1, 2014 at 20:54
Try this once: Bitmap bitmap = new Bitmap(clientWidth, clientHeight, PixelFormat.Format24bppRgb); — Muepe
– Muepe, Commented Apr 1, 2014 at 21:04

Muepe · Accepted Answer · 2014-04-01 21:07:21Z

2

In your C++-Code you have: bmi.biBitCount = 24; but in C# you use the default pixelformat for the bitmap. This is PixelFormat32bppArgb. That means that it uses 32 bits per pixel. If you use

Bitmap bitmap = new Bitmap(clientWidth, clientHeight, PixelFormat.Format24bppRgb);

This might fix the problem.

answered Apr 1, 2014 at 21:07

Muepe

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