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Since D2X-XL now prints diagnostic messages before being able to open a program window or render text,
I was in need of a function that would work like a Windows message box for Linux too. This sounded easier than it was - way easier.
Actually there is no simple way to programmatically have the operating system display a message box for an application on Linux.
There are several window manager libraries (Motif, Gtk, Qt4, wxWidgets) but all of these are centered around building an application
with a main window and a message loop, which D2X-XL didn't have at the stage where I needed the message box (or actually anywhere later,
at least not in the form required for these GUI libraries.)
In the end I decided to use Motif for the task as it is a very common GUI API and most Linux window managers can handle it.
Creating a message box proved to be rather easy, but I wanted more than that: For D2X-XL diagnostic output I needed a bigger, scrollable
text viewing area. An additional problem was posed by Motif's behavior to only display my message box when I started its event loop
and terminated D2X-XL when the message box was closed by the user; something I definitely had to work around and allow D2X-XL to continue
its operation when it was only displaying warnings and not critical errors. Finally, I didn't want the message box to have minimize, maximize
and close window controls, but simply a 'close' button below the message text.
After days of poking around in the internet I finally found some code in the Motif programmer's manual that I only had to adapt a little
to get what I want.
First of all the required include files and global data:
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#include <Xm/Xm.h>
#include <Xm/MwmUtil.h>
#include <Xm/MainW.h>
#include <Xm/CascadeB.h>
#include <Xm/MessageB.h>
#include <Xm/RowColumn.h>
#include <Xm/Form.h>
#include <Xm/PushBG.h>
#include <Xm/LabelG.h>
#include <Xm/PanedW.h>
#include <Xm/Text.h>
#include <Xm/DialogS.h>
#include <Xm/Command.h>
static XtAppContext appShell;
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MsgSize determines the number of lines contained in the message as well as the length of the longest line.
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static int MsgSize (char* pszMsg, int& nCols)
{
if (!(pszMsg && *pszMsg))
return 0;
int nRows = 1;
nCols = 0;
for (char* p = pszMsg; *p && (pszMsg = strchr (p, '\n')); nRows++, p = ++pszMsg) {
if (nCols < pszMsg - p)
nCols = pszMsg - p;
}
return nRows;
}
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DestroyShell is the callback function for the message dialog's cancel button. Since this is not a predefined Motif dialog, the
'widget' parameter is not the dialog itself. That is only done by Motif dialog callbacks. Here in the real world, the callback routine
is called directly by the widget that was invoked. Thus, we must pass the dialog as the client data to get its handle. (We could get it
using GetTopShell() but this way is quicker, since it's immediately available.)
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void DestroyShell (Widget widget, XtPointer clientData, XtPointer callData)
{
Widget shell = (Widget) clientData;
XtDestroyWidget (shell);
XtAppSetExitFlag (appShell);
}
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XmMessageDialog builds a dialog containing a scrollable, non editable text widget and a close button. It will also disable the
dialog's close, minimize and maximize functions. The popup window consists of a dialog shell which is derived from a vendor shell
and hence allows window decoration manipulation. The delete window protocol response is set to XmDESTROY to make sure that the window
goes away appropriately. Otherwise, it's XmUNMAP which means it'd be lost forever, since we're not storing the widget globally or
statically to this function.
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Widget XmMessageDialog (const char* pszMsg, int nRows, int nCols, bool bError)
{
Widget msgBox, pane, msgText, form, widget;
void DestroyShell(Widget, XtPointer, XtPointer);
Arg args [10];
int n = 0;
int i;
const char* szCaption [] = {"Warning", "Error"};
Widget topWid = XtVaAppInitialize (&appShell, "D2X-XL", NULL, 0, &argc, argv, NULL, NULL);
xtSetArg (args [0], XmNdeleteResponse, XmDESTROY);
msgBox = XmCreateDialogShell (topWid, const_cast<char*>(szCaption [bError]), args, 1);
XtVaSetValues (msgBox, XmNmwmDecorations,
MWM_DECOR_BORDER | MWM_DECOR_RESIZEH | MWM_DECOR_TITLE, NULL);
XtVaGetValues (msgBox, XmNmwmFunctions, &i, NULL);
i &= ~(MWM_FUNC_ALL | MWM_FUNC_MINIMIZE | MWM_FUNC_MAXIMIZE | MWM_FUNC_CLOSE);
XtVaSetValues (msgBox, XmNmwmFunctions, i, NULL);
// Create a PanedWindow to manage the stuff in this dialog. PanedWindow won't let us set these to 0!
XtSetArg (args [0], XmNsashWidth, 1);
// Make small so user doesn't try to resize
XtSetArg (args [1], XmNsashHeight, 1);
pane = XmCreatePanedWindow (msgBox, const_cast<char*>("pane"), args, 2);
// Create a RowColumn in the form for Label and Text widgets. This is the control area.
form = XmCreateForm (pane, const_cast<char*>("form1"), NULL, 0);
// prepare the text for display in the ScrolledText object we are about to create.
n = 0;
XtSetArg (args [n], XmNscrollVertical, True); n++;
XtSetArg (args [n], XmNscrollHorizontal, False); n++;
XtSetArg (args [n], XmNeditMode, XmMULTI_LINE_EDIT); n++;
XtSetArg (args [n], XmNeditable, False); n++;
XtSetArg (args [n], XmNcursorPositionVisible, False); n++;
XtSetArg (args [n], XmNwordWrap, True); n++;
XtSetArg (args [n], XmNvalue, pszMsg); n++;
XtSetArg (args [n], XmNrows, min (nRows, 30)); n++;
XtSetArg (args [n], XmNcolumns, min (nCols, 120)); n++;
msgText = XmCreateScrolledText (form, const_cast<char*>("help_text"), args, n);
// Attachment values must be set on the Text widget's parent, the ScrolledWindow.
// This is the object that is positioned.
XtVaSetValues (XtParent (msgText),
XmNleftAttachment, XmATTACH_FORM,
XmNtopAttachment, XmATTACH_FORM,
XmNrightAttachment, XmATTACH_FORM,
XmNbottomAttachment, XmATTACH_FORM,
NULL);
XtManageChild (msgText);
XtManageChild (form);
// Create another form to act as the action area for the dialog
XtSetArg (args [0], XmNfractionBase, 5);
form = XmCreateForm (pane, const_cast<char*>("form2"), args, 1);
// The OK button is under the pane's separator and is centered in the form. It spreads from position
// 1 to 2 along the bottom (the form is split into 5 separate grids via XmNfractionBase upon creation).
widget = XmCreatePushButtonGadget (form, const_cast<char*>("Close"), NULL, 0);
XtVaSetValues (widget,
  XmNtopAttachment, XmATTACH_FORM,
  XmNbottomAttachment, XmATTACH_FORM,
  XmNleftAttachment, XmATTACH_POSITION,
  XmNleftPosition, 2,
  XmNrightAttachment, XmATTACH_POSITION,
  XmNrightPosition, 3,
  XmNshowAsDefault, True,
  XmNdefaultButtonShadowThickness, 1,
  NULL);
XtManageChild (widget);
XtAddCallback (widget, XmNactivateCallback, DestroyShell, (XtPointer) msgBox);
// Fix the action area pane to its current height -- never let it resize
XtManageChild (form);
XtVaGetValues (widget, XmNheight, &h, NULL);
XtVaSetValues (form, XmNpaneMaximum, h, XmNpaneMinimum, h, NULL);
// This also pops up the dialog, as it is the child of a DialogShell
XtManageChild (pane);
return topWid;
}
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The purpose of the following callback is to tell the application event loop to quit without terminating the entire program. This callback
is invoked when the message box's close button is clicked.
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void XmCloseMsgBox (Widget w, XtPointer clientData, XtPointer callData)
{
XtAppSetExitFlag (appShell);
}
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XmMessageBox decides whether the message to be displayed is small enough to warrant a simple message box or should rather be displayed
in a bigger, scrolling text display.
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void XmMessageBox (const char* pszMsg, bool bError)
{
Widget topWid;
int nRows, nCols;
nRows = MsgSize (const_cast<char*>(pszMsg), nCols);
if ((nRows > 3) || (nCols > 360))
topWid = XmMessageDialog (pszMsg, nRows, nCols, bError);
else { // use the built-in message box
topWid = XtVaAppInitialize (&appShell, "D2X-XL", NULL, 0, &argc, argv, NULL, NULL);
// setup message box text
Arg args [1];
XmString xmString = XmStringCreateLocalized (const_cast<char*>(pszMsg));
XtSetArg (args [0], XmNmessageString, xmString);
// create and label message box
Widget xMsgBox = bError
? XmCreateErrorDialog (topWid, const_cast<char*>("Error"), args, 1)
: XmCreateWarningDialog (topWid, const_cast<char*>("Warning"), args, 1);
// remove text resource
XmStringFree (xmString);
// remove help and cancel buttons
XtUnmanageChild (XmMessageBoxGetChild (xMsgBox, XmDIALOG_CANCEL_BUTTON));
XtUnmanageChild (XmMessageBoxGetChild (xMsgBox, XmDIALOG_HELP_BUTTON));
// add callback to the "close" button that signals closing of the message box
XtAddCallback (xMsgBox, XmNokCallback, XmCloseMsgBox, NULL);
XtManageChild (xMsgBox);
XtRealizeWidget (topWid);
}
XtAppMainLoop (appShell);
XtUnrealizeWidget (topWid);
XtDestroyApplicationContext (appShell);
}
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SetCloseCallBack intercepts the window manager's close signal to a window. It can be used to prevent the entire application being
terminated when the main is closed.
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#include <Xm/Protocols.h>
Boolean SetCloseCallBack (Widget shell, void (*callback) (Widget, XtPointer, XtPointer))
{
extern Atom XmInternAtom (Display *, char *, Boolean);
if (!shell)
return False;
Display* disp = XtDisplay (shell);
if (!disp)
return False;
// Retrieve Window Manager Protocol Property
Atom prop = XmInternAtom (disp, const_cast<char*>("WM_PROTOCOLS"), False);
if (!prop)
return False;
// Retrieve Window Manager Delete Window Property
Atom prot = XmInternAtom (disp, const_cast<char*>("WM_DELETE_WINDOW"), True);
if (!prot)
return False;
// Ensure that Shell has the Delete Window Property
// Necessary since some Window managers are not fully XWM Compilant (olwm for instance is not)
XmAddProtocols (shell, prop, &prot, 1);
// Now add our callback into the Protocol Callback List
XmAddProtocolCallback (shell, prop, prot, callback, NULL);
return True;
}
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To be able to compile and link this code you will need to install e.g. the OpenMotif and OpenMotif-devel packages and use
the Xm, Xt, and X11 libraries (-lXm -lXt -lX11).
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