Internals(3) User Contributed Perl Documentation Internals(3)NAME
CallingTk - what is Perl Tk interface doing when you call Tk func‐
tions.
This information is worse than useless for "perlTk" users, but can of
some help for people interested in using modified Tk source with
"perlTk".
This document is under construction. The information is believed to be
pertinent to the version of "portableTk" available when it was created.
All the details are subject to change.
DESCRIPTION
PreCompiling
Before the actual compilation stage a script scans the source and
extracts the subcommands of different commands. This information
resides in the file "pTk/Methods.def".
Compilation
During compilation the above file is included in the source of
booting routine of dynamic (or static) library. More precisely, the
booting code of module "Tk" calls the subroutine Boot_Glue() from
the module "tkGlue.c", and this subroutine includes the file (with
appropriate macro definitions).
Inside "use Tk;"
The module bootstraps the C code, then loads the Perl libraries.
The heart of the Perl code is contained in the "Tk::Widget"
library, all the widgets inherit from this module. Code for
toplevels is loaded from "Tk::MainWindow".
During bootstrap of the C glue code the "Xevent::?" codes and a
handful of "Tk::Widget" and "Tk::Image" routines are defined. (Much
more XSUBs are created from "Tk.xs" code.) The widget subcommands
are glued to Perl basing on the list included from "pTk/Meth‐
ods.def". In fact all the subcommands are glued to XSUBs that are
related to the same C subroutine XStoWidget(), but have different
data parts.
During the Perl code bootstrap the method "Tk::Widget::import" is
called. This call requires all the code from particular widget
packages.
Code from the widget packages calls an obscure command like
(bless \"Text")->WidgetClass;
This command (actually Tk::Widget::WidgetClass()) creates three
routines: Tk::Widget::Text(), Tk::Widget::isText(), and
Tk::Text::isText(). The first one is basically "new" of "Tk::Text",
the other two return constants. It also puts the class into deposi‐
tory.
Inside "$top = MainWindow->new;"
This is quite intuitive. This call goes direct to "Tk::MainWin‐
dow::new", that calls XSUB "Tk::MainWindow::CreateMainWindow", that
calls C subroutine Tk_CreateMainWindow(). It is a "Tk" subroutine,
so here black magic ends (almost).
The only remaining black magic is that the "Tk" initialization rou‐
tine creates a lot of commands, but the subroutine for creation is
usurped by portableTk and the commands are created in the package
"Tk". They are associated to XSUBs that are related to one of three
C subroutines XStoSubCmd(), XStoBind(), or XStoTk(), but have dif‐
ferent data parts.
The result of the call is blessed into "Tk::MainWindow", as it
should.
Inside "$top->title('Text demo');"
The package "Tk::Toplevel" defines a lot of subroutines on the fly
on some list. All the commands from the list are converted to the
corresponding subcommands of "wm" method of the widget. Here sub‐
command is a command with some particular second argument (in this
case "title"). Recall that the first argument is $self.
Now "Tk::Toplevel" @ISA "Tk::Widget", that in turn @ISA "Tk". So a
call to "$top->wm('title','Text demo')" calls "Tk::wm", that is
defined during call to Tk_CreateMainWindow(). As it is described
above, the XSUB associated to XStoSubCmd() is called.
This C routine is defined in "tkGlue.c". It gets the data part of
XSUB, creates a "SV" with the name of the command, and calls
Call_Tk() with the XSUB data as the first argument, and with the
name of XSUB stuffed into the Perl stack in the place there "tk"
expects it. (In fact it can also reorder the arguments if it thinks
it is what you want).
The latter procedure extracts name of "tk" procedure and "client‐
Data" from the first argument and makes a call, using Perl stack as
"argv" for the procedure. A lot of black magic is performed after‐
wards to convert result of the procedure to a Perl array return.
Inside "$text = $top->Text(background => $txtBg);"
Above we discussed how the command "Tk::Widget::Text" is created.
The above command calls it via inheritance. It is translated to
Tk::Text::new($top, background => $txtBg);
The package "Tk::Text" has no method "new", so the "Tk::Wid‐
get::new" is called. In turn it calls "Tk::Text->DoInit($top)",
that is "Tk::Widget::DoInit(Tk::Text,$top)", that initializes the
bindings if necessary. Then it creates the name for the widget of
the form ".text0", and calls "Tk::text('.text0', background =>
$txtBg)" (note lowercase). The result of the call is blessed into
"Tk::Text", and the method "bindtags" for this object is called.
Now the only thing to discuss is who defines the methods "text" and
"bindtags". The answer is that they are defined in "tkWindow.c",
and these commands are created in the package "Tk" in the same
sweep that created the command "Tk::wm" discussed above.
So the the same C code that corresponds to the processing of corre‐
sponding TCL commands is called here as well (this time via
"XStoTk" interface).
Inside "$text->insert('insert','Hello, world!');"
As we discussed above, the subcommands of widget procedures corre‐
spond to XSUB "XStoWidget". This XSUB substitutes the first argu‐
ment $text (that is a hash reference) to an appropriate value from
this hash, adds the additional argument after the first one that
contains the name of the subcommand extracted from the data part of
XSUB, and calls the corresponding Tk C subroutine via "Call_Tk".
Ilya Zakharevich <ilya@math.ohio-state.edu>
perl v5.8.8 2004-02-28 Internals(3)
