How can I use .Net system.drawing.drawstring to write right-to-left string (project is a dll)?

Hi I need to create a bitmap file from an string, currently I'm using

Bitmap b = new Bitmap(106, 21);
Font f = new Font("Tahoma",5 );
StringFormat sf = new StringFormat();            
int faLCID = new System.Globalization.CultureInfo("fa-IR").LCID;
sf.SetDigitSubstitution(faLCID, StringDigitSubstitute.National);            
Brush brush = Brushes.Black;
Point pos = new Point(2, 2);
Graphics c = Graphics.FromImage(b);                        
c.FillRectangle(Brushes.White, 0, 0, m_width, m_length);
c.DrawString(stringText, f, brush, pos,sf);

it works but the problem is it is writing left to right. How can I make DrawString() to write right-to-开发者_如何学Pythonleft? thanx

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Pass StringFormatFlags.DirectionRightToLeft.