Thread: Writing Raw Bitmap File

I've been doing win32 for a little while now and I've just encountered a bit of a problem making a program to take a screenshot. Even after finding a convenient msdn article: http://msdn.microsoft.com/library/de...tmaps_7zfp.asp I was still unable to do this. Currently with the help of these MSDN functions, it writes a corrupted (black?) bitmap file. Several other attempts at creating the headers and getting it all written out resulted in empty or corrupted. The souce is attached, originally I was just screwing around with the effect repeated BitBlt's GetDC(GetDesktopWindow()) but now I want to get that into a bitmap file.

Code:

void Screenshot(HDC hDC, HWND hwnd)
{
    SIZE size; 
	RECT rect;
	GetClientRect(hwnd, &rect);
    size.cx = GetSystemMetrics(SM_CXSCREEN);
    size.cy = GetSystemMetrics(SM_CYSCREEN);
	HDC hdcMemory = GetDC(GetDesktopWindow());
    HBITMAP hBitmap = CreateCompatibleBitmap(hdcMemory, size.cx, size.cy);
    if(hBitmap) {
		BitBlt(hDC, 0, 0, size.cx, size.cy, hdcMemory, 0, 0, SRCCOPY);
		//Save(hwnd, CreateInfoHeader(hwnd, hBitmap), hBitmap, hDC);
        DeleteDC(hdcMemory);        
        DeleteObject(hBitmap);
    }
    ReleaseDC(NULL, hDC);
}

You're saving an empty bitmap! You copy the screen image to your window but not the memory bitmap. Here is an edited, commented but untested version of your function:

Code:

void Screenshot(HDC hDC, HWND hwnd)
{
	RECT rect;
	GetClientRect(hwnd, &rect);  /* Not currently used */

	/* Get the size of the screen */
	SIZE size; 
	size.cx = GetSystemMetrics(SM_CXSCREEN);
	size.cy = GetSystemMetrics(SM_CYSCREEN);

	/* Get a device context for the screen */
	HDC hdcScreen = CreateDC(TEXT("DISPLAY"), NULL, NULL, NULL);

	/* Create a memory bitmap and put it in a memory DC so we can draw on it */
	HDC hdcShot = CreateCompatibleDC(hdcScreen);
	HBITMAP hBitmapShot = CreateCompatibleBitmap(hdcScreen, size.cx, size.cy);
	HBITMAP hBitmapOld = (HBITMAP) SelectObject(hdcShot, hBitmapShot);

	/* Copy the screen image to our memory bitmap */
	BitBlt(hdcShot, 0, 0, size.cx, size.cy, hdcScreen, 0, 0, SRCCOPY);

	/* You can copy the screen to your window (hDC) here if needed */
	/* BitBlt(hDC, 0, 0, size.cx, size.cy, hdcScreen, 0, 0, SRCCOPY); */

	/* Save our memory bitmap to file */
	Save(hwnd, CreateInfoHeader(hwnd, hBitmapShot), hBitmapShot, hdcShot);

	/* Cleanup memory bitmap and DC */
	SelectObject(hdcShot, hBitmapOld);
	DeleteObject(hBitmapShot);
	DeleteDC(hdcShot);

	/* Cleanup screen DC */
	DeleteDC(hdcScreen);
}