gdi+ draws string inverted - c++

Question

I am trying to write text to a bitmap i am getting from an usb camera using directshow.
The problem is that the text is mirror inverted upside-down and i don't know why.
Here is the code that writes the text:
BITMAPINFOHEADER bih = m_videoInfo.bmiHeader;
Bitmap bmp(bih.biWidth, bih.biHeight, m_stride, m_pixFmt, pBuffer);
Graphics g(&bmp);
if (this->introTimer->timeToDo())
{
RectF pos(10, 10, 100, 100);
SolidBrush brush(Color::Black);
Font font(FontFamily::GenericSerif(), 30);
hr = g.DrawString(this->introText, -1, &font, pos, StringFormat::GenericDefault(), &brush);
return hr;
}
I am not sure if my code is the only thing that affects the drawing of the string. Maybe there is some configuration or something.
Update
I tried using a negative height as suggested by Hans Passant. The result is that the text is not written at all.

Answer 1

The obvious thing to do would be to set the transformation on GDI+.
Essentially you need to invert the Y axis (though by doing this it would now draw off screen). So you need to then translate it down by the window size.
Something like this:
graphics.Transform = new Matrix2D( 1, 0,
0, -1,
0, -windowHeight );
Then draw as normal.
(Its worth noting I'm suggesting this without testing it. The y translation may not be negative so try both!).

Answer 2

The scanlines are stored upside down, with the first scan (scan 0) in memory being the bottommost scan in the image. This is another artifact of Presentation Manager compatibility. GDI automatically inverts the image during the Set and Get operations.
About the suggestion from Hans Passant, did you try negative height in position?
He suggests to use negative height in bih.
BITMAPINFOHEADER bih = m_videoInfo.bmiHeader;
bih.biHeight = -bih.biHeight;
Bitmap bmp(bih.biWidth, bih.biHeight, m_stride, m_pixFmt, pBuffer);
...
Also copying another solution from this page if it helps
void BitmapControl::OnPaint()
{
EnterCriticalSection (&CriticalSection);
if (_handleBMP)
{
CPaintDC dc(this);
//dc.SetMapMode(MM_ISOTROPIC);
dc.SetMapMode(MM_LOENGLISH);
CDC dcMem;
dcMem.CreateCompatibleDC(&dc);
CRect rect;
GetClientRect(&rect);
dc.DPtoLP(&rect);
CBitmap* pBmpOld = dcMem.SelectObject(CBitmap::FromHandle(_handleBMP));
//tst
dc.SetStretchBltMode(COLORONCOLOR);
//BitBlt(dc,rect.left,-0,rect.Width(),rect.Height(),dcMem,rect.left,rect.top,SRCCOPY); //works with MM_TEXT but upsidedown
BitBlt(dc,0,rect.bottom,rect.Width(),-rect.Height(),dcMem,0,0,SRCCOPY); //works with MM_LOENGLISH
dcMem.SelectObject(pBmpOld);
DeleteDC(dc);
DeleteDC(dcMem);
DeleteObject(_handleBMP);
DeleteObject(pBmpOld);
_handleBMP = NULL;
}
LeaveCriticalSection (&CriticalSection);
}