Chapter 7. Output to Display

66

7.2 X Clients

The way to develop X clients can differ drastically dependent on the toolkits to be used. At first,

Xlib style programming is discussed since Xlib is the fundamental for all other toolkits. Then a

few toolkits are discussed.

7.2.1 Xlib programming

X itself is already internationalized. X11R5 has introduced an idea of 'fontset' for internationalized

text output. Thus all what X clients have to do is to use the 'fontset' related functions.

The most important part for internationalization of displaying for X clients is the usage of interna 

tionalized XFontSet related functions introduced since X11R5 instead of conventional XFontStruct 

related functions.

The main feature of XFontSet is that it can handle multiple fonts at the same time. This is related

to the distinction between coded character set (CCS) and character encoding scheme (CES) which

I wrote at the section of `Basic Terminology' on page

9

. Some encodings in the world use multiple

coded character sets at the same time. This is the reason we have to handle multiple X fonts at the

same time.

3

Another significant feature of XFontSet is that it is locale (LC_CTYPE) sensible. This means that

you have to call

setlocale()

before you use XFontSet related functions. And more, you have

to specify the string you want to draw as a multibyte character or a wide character.

In the conventional

XFontStruct

model, an X client opens a font using

XLoadQueryFont()

,

draw a string using

XDrawString()

, and close the font using

XFreeFont()

. On the other hand,

in the internationalized

XFontSet

model, an X client opens a font using

XCreateFontSet()

,

draw a string using

XmbDrawString()

, and close the font using

XFreeFontSet()

. The follow 

ing are a concise list of substitution.

XFontStruct

 >

XFontSet

XLoadQueryFont()

 >

XCreateFontSet()

  both of

XDrawString()

and

XDrawString16

 > either of

XmbDrawString()

or

XwcDrawString()

  both of

XDrawImageString()

and

XDrawImageString16

 > either of

XmbDrawImageString()

or

XwcDrawImageString()

Note that

XFontStruct

is usually used as a pointer, while

XFontSet

itself is a pointer.

3

Though UTF 8 is an encoding with single CCS, the current version of XFree86 (4.0.1) needs multiple fonts to handle

UTF 8.