修改字体的方法

不很完善，没有错误处理

- (NSFont*) changeUsrFont:(NSFont*)usrFont
    sFontName:(NSString*) fontName
     bBold:(BOOL) bold
      bItalic:(BOOL) italic
      size:(double) dFontSize
{ 
 NSFontManager* FM = [NSFontManager sharedFontManager];
 
 dFontSize = (dFontSize < 1.0) ? 1.0 : dFontSize;
 
 NSFontTraitMask s = 0;
 
 if (italic)
 {
  s |= NSItalicFontMask;
 }
 else
 {
  s |= NSUnitalicFontMask;
 }
 
 if (bold)
 {
  s |= NSBoldFontMask;
 }
 else
 {
  s |= NSUnboldFontMask;
 }
 
 if (!usrFont)
 {
  usrFont = [FM fontWithFamily:fontName traits:s weight:5 size:dFontSize];
  
  if (!usrFont) // this is bad; the wrong font name ends up in the font popups - FIXME please!
  {
   /* Oops!  We don't have that font here.
   * first try "Times New Roman", which should be sensible, and should
   * be there unless the user fidled with the installation
   */
   NSLog (@"Unable to find font \"%s\".", fontName);
   
   usrFont = [[NSFontManager sharedFontManager] fontWithFamily:@"Times" traits:s weight:5 size:dFontSize];
  }
 }
 else
 {
  usrFont = [FM convertFont:usrFont toFamily:fontName];
  usrFont = [FM convertFont:usrFont toHaveTrait:s];
  usrFont = [FM convertFont:usrFont toSize:dFontSize];
 }
 
 return usrFont; 
}