The application may choose to specify the font used in rendering the
IntuiText, or it may choose to use the default font for the system.

To use the default font, set the ITextFont field to NULL.  Some care must
be taken when using the default font.  When an IntuiText object is
rendered and no font is specified, the text will be rendered in the font
set in the RastPort.

If the RastPort font is NULL, the text will be rendered using
GfxBase->DefaultFont.  Also, IntuiTextLength() always uses
GfxBase->DefaultFont when ITextFont is NULL.  The application must have
open the graphics library in order to check the default font in GfxBase.
(See the graphics library chapter for more information.)

To use a specific font for this text, place a pointer to an initialized
TextAttr structure in the ITextFont field.  Intuition will only use the
specified font if it is available through a call to the OpenFont()
routine.  To use a font from disk, the application must first open the
font using the OpenDiskFont() function.  For more information about using
fonts, see the "Graphics Library and Text" chapter in this manual.