Viewer for plain ASCII

	The viewer is an applet corresponding to W3A/V. It works by
	opening an XmText widget and displaying the text in it.

	[[instance]] is an array that maps IDs to XmText widgets.
	[[ninstances]] is the number of assigned IDs, except that
	there may be lower numbered IDs that have been freed again.
	When [[closePlain]] is called, the corresponding widget
	element of [[instance]] is set to [[NULL]], so that the ID can
	be reused.

	[[openPlain]] finds the first unused element in [[instance]].
	The index will be the ID that is passed to the caller. It then
	asks for a work area and creates an XmText widget under it.

	[[writePlain]] adds text to the XmText widget.

	[[closePlain]] destroys the XmText widget and marks the
	element in [[instance]] as free, by setting it to [[NULL]].

<<*>>=
#include <Xm/Xm.h>
#include <Xm/Text.h>
#include <w3a.h>

#define MAXINSTANCE 30

static struct {Widget w; int nchars;} instance[MAXINSTANCE];
static int ninstances = 0;


Bool initPlain()
{
    /* Nothing to initialize */
}


long openPlain(const W3ADocumentInfo info, W3AWindow work_area)
{
    Widget w;
    Arg args[3];
    int i, nargs = 0;

    for (i = 0; i < ninstances; i++) if (! instance[i].w) break;
    XtSetArg(args[nargs], XmNeditMode, XmMULTI_LINE_EDIT); nargs++;
    XtSetArg(args[nargs], XmNeditable, FALSE); nargs++;
    w = XmCreateScrolledText(work_area, "plain", args, nargs);
    XtManageChild(w);
    XtRealizeWidget(w);
    instance[i].w = w;
    instance[i].nchars = 0;
    if (i == ninstances) ninstances++;
    return i;
}


int writePlain(long id, const char *buf, size_t nbytes)
{
    char *s, *t;

    s = XtMalloc(nbytes + 1);
    *s = '\0';
    strncat(s, buf, nbytes);
    for (t = s; *t; t++) if (*t == '\015') *t = ' ';
    XmTextInsert(instance[id].w, instance[id].nchars, s);
    XtFree(s);
    instance[id].nchars += nbytes;
    return nbytes;
}


Bool closePlain(long id)
{
    int i;

    XtDestroyWidget(instance[id].w);
    instance[id].w = NULL;
}