XTENT(1) XTENT(1)
19 July 1993
NAME
xtent - X* resource based specification language
X Window System is a trademark of the Massachusetts Institute of
Technology.
SYNOPSIS
xtent [ X-resource-file ] [ -input X-resource-file ] [ -class
process-class-name ]
OPTIONS
X-resource-file
Use the contents of X-resource-file as the source for the
process.
-input X-resource-file
Use the contents of X-resource-file as the source for the
process.
-class process-class-name
Use process-class-name as the X class for this process. If no
input file is specified, input is assumed to come from
standard input.
DESCRIPTION
xtent is an interpreter that is used to construct X Toolkit (Xt) based
applications. The syntax of input programs follows that of the X
resource database. See the Xlib manual for a complete description of
the X resource syntax. xtent extends the X resource database
semantics to include all of the X Toolkit functions for creating and
manipulating widgets. See the X Toolkit manual and the xtent
reference manual for a complete list of functions. An application
developer must have copies of the xtent manual, the X Toolkit manual,
and the programmers reference manual for the widget set that is to be
used. These are required for looking up the details of the graphics
objects and the function calls. This man page, as with the man page
for any language processor, primarily gives the options for invoking
the processor, in this case an interpreter. The following few
paragraphs will give a small bit of detail on what xtent accepts as
input. This is not a substitute for the manuals mentioned above. X
resource entries resemble C structured data types. The following
example will help to demonstrate this point.
red: #FF0000
A.B.x: 10
A.B.y: 9
A.B.color: green
A*Sensitive: True
The first line sets the variable red to the string #FF0000. The next
four lines create a B structure within a structure A. The B structure
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XTENT(1) XTENT(1)
19 July 1993
includes x and y values and a color. The last entry says that under
the A structure, any element named Sensitive in any structure will be
set to True by default. X resources are at a much higher level of
abstraction than C code. The following piece of resource code is a
good example:
*font: 6x13B
This line will result in the font 6x13B being used wherever a font is
required, but not explicitly specified. Of course, this sort of
parameterization is inherently declarative. The resource mechanism is
definitely limited in terms of its use as a programming language. The
majority of the X community uses resources only for specifying
parameters to widgets, Xt graphics objects. The parameterization,
however, has a simple object-oriented style that can be extended for
programming. Consider the following line:
xtent.allowShellResize: True
This line allows the toplevel window (actually shell widget) to be
resized when it is required by the application. The sense of the line
is to set a variable, allowShellResize, associated with the
application xtent to True. Notice that this implies that the string
True will be converted to an appropriate type. In object-oriented
terms, one could also say, that the allowShellResize procedure
associated with the object xtent is called with or sent the message
True. This object/message notion can also be written in a style more
closely matching that of C++:
object.procedure: message (or arguments)
Using this syntax and semantics xtent includes all of the procedures
required to do Xt level specifications (and then some).
XtCreateManagedWidget(), one of the functions used to create widgets,
might be used in an application as follows:
xtent.Hello.XtCreateManagedWidget: xmPushButton
The line causes a widget with the name ``Hello'' to be created. The
parent widget is the toplevel widget for the xtent application. The
widget class is xmPushButton. The C interface to the X toolkit uses
the following function call to create the widget.
Hello = XtCreateManagedWidget ("Hello",
XmPushButtonWidgetClass,
parent,
args, arg-count);
The C based XtCreateManagedWidget() interface has five parameters:
object name, object class, parent object, argument array, and arugment
count. Using xtent, the name is given on the left hand or object side
of the expression. As widget names are hierarchical, the parent
widget name is included in the widget name, and so it does not have to
be provided. (The widgets in Xt applications form a tree-like data
structure. The toplevel or shell widgets have child widgets, which
may also have children. A pushbutton widget, within a form widget,
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XTENT(1) XTENT(1)
19 July 1993
within the toplevel xtent widget might be specified by the following
string, xtent.form.button or .form.button.) In the C version, the
args array is for setting widget parameters. The resource
parameterization mechanism handles that in xtent. On a function by
function basis, xtent can be argued to be conceptually simpler. The
one line xtent entry above is all that is required to specify a
complete (one widget) Xt program. The same program written directly
in C using the X toolkit takes about a page and a half of code. Using
X alone takes 5 or 6 pages. Some Xt functions require more than one
argument. In those cases, xtent uses a syntax that is similar to that
used by C.
.image.XtTranslateCoords: (25, 33, x, y)
The line above calls the function XtTranslateCoords() for the widget
xtent.image. The line above is used to translate widget specific
coordinates into display specific coordinates. XtTranslateCoords
always takes four arguments. However, some functions, for example
XtGetValues take a variable number of arguments. These VARARGS style
functions are handled as they are in C. Arguments are simply added by
separating the arguments by commas. xtent is best used for
manipulating widgets, but it can be used to handle other the arbitrary
programming tasks. See the sections of the xtent reference manual
describing functions for program control, calculations, string
manipulation, and input and output. The usual ``Hello World!''
example can be written as follows:
.XtPrint: Hello World!
SEE ALSO
See X(1) and xrdb(1) for a discussion of X resources.
DIAGNOSTICS
xtent complains when it cannot open a program or source file, when
common syntax errors occur, when object or function names cannot be
found, when illegal comparisons are made, or type conversions cannot
be accomplished.
BUGS
Errors that occur within the widget set usually result in segmentation
violations. xtent catches these errors, prints that it caught the
segmentation violation signal, and exits. All other deadly signals
are handled in the same manner.
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