84 CHAPTER 7. GRAPHICAL USER INTERFACE DESIGN IN SCHEME

Feel free to write variations of the programs we show here. This will help you

learn how to  think  in Scheme. Programming is a skill that is best learned by

doing rather than by reading alone.

7.3

Windows

Window are the most basic component of Graphical User Interfaces. All other

components must appear inside a window and any particular GUI might use

several different windows (e.g. help windows,  about  windows, file selection

windows, warning windows, editting windows).

The most basic window contains just a title (which is a string that usually

appears in the title bar). The following code creates a window with the title

 Hello , sets is size to be 300 pixels wide by 400 pixels high, and makes it appear

on the screen:

(define w (window "Hello"))

(.resize w 300 400)

(.show w)

Note that we have used the  define  syntax to give the name  w  to the window.

This name is need when we resize the window and make it visible in the following

two expressions. We will see many more windows below, so we don't dwell any

further on them at this point.

7.4

Labels

A label is a component used to display some text on the GUI. For example, the

following program creates a window with the text  Hello  in the titlebar and

the phrase  Hello again  in the inside of the window:

(define w (window "Hello"

(label "Hello again")))

(.resize w 300 400)

(.show w)

The first argument of the  label  procedure must be the string that will appear

on the label. We will see below that one can also specify the font and the color

of a label by adding more arguments to the  label  procedure.

7.5

Fonts

There are nine built in fonts that you can use in the JLIB library, and for each

font you can pick any font size (as long as it is a positive whole number). These

fonts are:

(Helvetica 23)

(HelveticaBold 100)

(HelveticaItalic 12)

(TimesRoman 29)

(TimesRomanBold 88)

(TimesRomanItalic 9)

(Courier 33)

(CourierBold 32)

(CourierItalic 33)