7 segment digit widget for X Windows

This project contains the implementation of a 7 segment display widget.

There is a test program called "xdigits" which uses 5 of these widgets to implement a simple digital clock.

There is another test program called "multi-zone-clock" which shows time values for multiple time zones. Currently, "multi" means 3, showing local time and GMT time, and New York Time (just because I needed these three times).

This code uses Xt, XLib and OSF/Motif library, which should be contained or at least installable via package from common Linux installations. These libraries are very old, and they will work even on Retro hardware (like my SUN Sunblade 100).

Build

Generate Makefile using xmkmf/imake:

-bash-5.3$ xmkmf
mv -f Makefile Makefile.bak
imake -DUseInstalled -I/usr/local/lib/X11/config

Build lib and executables:

make clean; make

Run xdigit clock program

./xdigit

The xdigit clock looks like this:

Run multi-zone-clock program

./multi-zone-clock

The multi-zone-clock looks like this:

For pretty colors see below in resources section.

Load resources with xrdb

# list existing definitions
xrdb --query
# add local ressources
xrdb --merge Digit.ad

Example content of Digit.ad:

*clockPanel.background: black
*digit.value: 0
*digit.showDecimalPoint: False
*digit.background: black
*digit.foreground: green
*clockTitle.background: black
*clockTitle.foreground: red

Example result:

Install Motif libs+includes (OpenSuse)

Using default OpenSuse packaging tooling, the following libs are needed for OSF/Motif:

Details on implementation

The definition of a digit

The resource XtNvalue controls the digit to be displayed. The value corresponds to the displayed number, except the following values:

• MINUS_VALUE : minus (segment 4)
• DECPOINT_VALUE : decimal point only (segment 8)
• DOUBLEPOINT_VALUE : double point (segments 9,10)

A number is displayed by drawing all required segments for that number. Segment indices:

        --1--
       |     |
       2 -9- 3
       |--4--|
       5 -*- 6 (*=10)
       |     |
        --7--  -8-

Each segment is drawn as a filled polygon of five points, starting with point index 0. Below are the points for horizontal and vertical segments:

Horizontal:

   origin
   *----------------+	+ segment_margin    +
   | 1------------2 |   +                   |                     
   | /            \ |                       | segment_height                      
   | \0          3/ |                       |
   | 5------------4 |                       |
   +----------------+                       +
                  +-+ segment_margin  
    ++ segment_delta   
   +<-segmentwidth->+

Vertical:

                         origin
   + segment_margin      *---------+   +
   +                     |   /\0   |   |
                         | 5|  |1  |   |
                         |  |  |   |   segment_height
                         |  |  |   |   |
                         | 4|  |2  |   | +
                         |   \/3   |   | + segment_delta
                         +---------+   +
                         +--+ segment_margin
                         +---------+ segment_width 

segment_height and segment width is outer box for segment drawing. segment_margin is the minimum distance between outer box and polygon for segment area, both in x and y dimension. segment_delta is the horizonal distance between point 0 and 1.

Loading fonts in X Windows (Motif)

List all available X Font names with

xlsfonts

See also own file listfonts.c .

To use a font, we need to load it. The font can be loaded by

#define SOMEFONT "-adobe-courier-bold-r-normal--24-240-75-75-m-150-iso8859-1"

char *someFont = SOMEFONT;
XFontStruct *font_info = XLoadQueryFont(display, someFont);

Then we need to set the font for the widget.

Motif does it slightly different that pure Xt. To set a font for a widget, we need to use the resource named XmNfontList.

First create a font list from the font:

XmFontList fontList = XmFontListCreate(font_info, XmFONTLIST_DEFAULT_TAG);

Then use it when creating the widget:

Arg wargs[7];
int n=0;

XmString xmstr = XmStringCreate(title, XmSTRING_DEFAULT_CHARSET);

XtSetArg( wargs[n], XmNlabelString, xmstr ); n++;
XtSetArg( wargs[n], XmNfontList, font_list ); n++;
// more resource setting removed ... 
XtCreateManagedWidget("clockTitle", xmLabelWidgetClass, compo, wargs, n);

Setting colors in widgets

Get existing values like seen below.

Define some structures to receive the values:

typedef struct _Resources {
	Pixel foreground;
	Pixel background;
} Resources;

static Resources theResources;

static XtResource resourceSpec[] = {
	{ XtNforeground, XtCForeground, XtRPixel, sizeof(Pixel),
	  XtOffsetOf(Resources, foreground),
	  XtRString, "XtDefaultForeground"},
	{ XtNbackground, XtCBackground, XtRPixel, sizeof(Pixel),
	  XtOffsetOf(Resources, background),
	  XtRString, "XtDefaultBackground"},
};

And the function call to fill these structures:

XtGetApplicationResources(toplevel, &theResources,
			   resourceSpec, XtNumber(resourceSpec), NULL, 0);

Use resources in Widget args:

XtSetArg( wargs[n], XtNforeground, theResources.foreground /*XtDefaultForeground*/ ); n++;
XtSetArg( wargs[n], XtNbackground, theResources.background ); n++;

Further reading

• ctime, gmtime and such functions - https://man7.org/linux/man-pages/man3/ctime.3.html
• Xt fonts and fontsets - https://ftp.zx.net.nz/rom/V4.0Fr1229_D1/DOCS/HTML/AQ0R4DTE/CRTGCHXX.HTM
• Xt Intrinsics manual - https://ftpmirror.your.org/pub/misc/bitsavers/pdf/hp/9000_hpux/x11/98794-90008_Programming_With_the_Xt_Intrinsics_Sep89.pdf
• Motif infos - https://en.wikipedia.org/wiki/Motif_(software)