Font Management

International text drawing is done using a set of one or more fonts, as needed for the locale of the text.

The two methods of internationalized drawing within the system environment allow clients to choose one of the static output widgets (for example, XmLabel) or to choose the DrawingArea widget to draw with any other primitive function.

Static output widgets require that text be converted to XmString.

The following information explains the mechanism for managing fonts using the Xlib routines and functions.

Creating and Freeing a Font Set

Xlib international text drawing is done using a set of one or more fonts, as needed for the locale of the text. Fonts are loaded according to a list of base font names supplied by the client and the charsets required by the locale. The XFontSet is an opaque type.

• The XCreateFontSet() function is used to create an international text drawing font set.

• The XFontsOfFontSet() function is used to obtain a list of XFontStruct structures and full font names given an XFontSet.

• To obtain the base font name list and the selected font name list given an XFontSet, use the XBaseFontNameListOfFontSet() function.

• To obtain the locale name given an XFontSet, use the XLocaleOfFontSet() function.

• The XLocaleOfFontSet() function returns the name of the locale bound to the specified XFontSet as a null-terminated string.

• The XFreeFontSet() function frees the specified font set. The associated base font name list, font name list, XFontStruct list, and XFontSetExtents, if any, are freed.

Obtaining Font Set Metrics

Metrics for the internationalized text drawing functions are defined in terms of a primary draw direction, which is the default direction in which the character origin advances for each succeeding character in the string. The Xlib interface is currently defined to support only a left-to-right primary draw direction. The drawing origin is the position passed to the drawing function when the text is drawn. The baseline is a line drawn through the drawing origin parallel to the primary draw direction. Character ink is the pixels painted in the foreground color and does not include interline or intercharacter spacing or image text background pixels.

The drawing functions are allowed to implement implicit text direction control, reversing the order in which characters are rendered along the primary draw direction in response to locale-specific lexical analysis of the string.

Regardless of the character rendering order, the origins of all characters are on the primary draw direction side of the drawing origin. The screen location of a particular character image may be determined with the XmbTextPerCharExtents() or XwcTextPerCharExtents() functions.

The drawing functions are allowed to implement context-dependent rendering, where the glyphs drawn for a string are not simply a combination of the glyphs that represent each individual character. A string of two characters drawn with the XmbDrawString() function may render differently than if the two characters were drawn with separate calls to the XmbDrawString() function. If the client adds or inserts a character in a previously drawn string, the client may need to redraw some adjacent characters to obtain proper rendering.

The drawing functions do not interpret newline characters, tabs, or other control characters. The behavior when nonprinting characters are drawn (other than spaces) is implementation-dependent. It is the client's responsibility to interpret control characters in a text stream.

To find out about context-dependent rendering, use the XContextDependentDrawing() function. The XExtentsOfFontSet() function obtains the maximum extents structure given an XFontSet. The XmbTextEscapement() and XwcTextEscapement() functions obtain the escapement in pixels of the specified text as a value. The XmbTextExtents() and XwcTextExtents() functions obtain the overall bounding box of the string's image and a logical bounding box (overall_ink_return and overall_logical_return arguments respectively). The XmbTextPerCharExtents() and XwcTextPerCharExtents() functions return the text dimensions of each character of the specified text, using the fonts loaded for the specified font set.