Посмотрите на CGContextSelectFont ниже:
void MyDrawText (CGContextRef myContext, CGRect contextRect)
{
float w, h;
w = contextRect.size.width;
h = contextRect.size.height;
CGAffineTransform myTextTransform;
CGContextSelectFont (myContext, "Helvetica-Bold", h/10, kCGEncodingMacRoman);
CGContextSetCharacterSpacing (myContext, 10);
CGContextSetTextDrawingMode (myContext, kCGTextFillStroke);
CGContextSetRGBFillColor (myContext, 0, 1, 0, .5);
CGContextSetRGBStrokeColor (myContext, 0, 0, 1, 1);
myTextTransform = CGAffineTransformMakeRotation (MyRadians (45));
CGContextSetTextMatrix (myContext, myTextTransform);
CGContextShowTextAtPoint (myContext, 40, 0, "Quartz 2D", 9);
}