Internals(3pm) User Contributed Perl Documentation Internals(3pm)
NAME
Tk::Internals - what is Perl Tk interface doing when you call Tk
functions.
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/Methods.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
depository.
Inside "$top = MainWindow->new;"
This is quite intuitive. This call goes direct to
"Tk::MainWindow::new", that calls XSUB
"Tk::MainWindow::CreateMainWindow", that calls C subroutine
Tk_CreateMainWindow(). It is a "Tk" subroutine, so here black magic
ends (almost).
The only remaining black magic is that the "Tk" initialization
routine creates a lot of commands, but the subroutine for creation
is usurped by portableTk and the commands are created in the package
"Tk". They are associated to XSUBs that are related to one of three
C subroutines XStoSubCmd(), XStoBind(), or XStoTk(), but have
different data parts.
The result of the call is blessed into "Tk::MainWindow", as it
should.
Inside "$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
subcommand 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
"clientData" from the first argument and makes a call, using Perl
stack as "argv" for the procedure. A lot of black magic is performed
afterwards 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 => $txtBg);
The package "Tk::Text" has no method "new", so the "Tk::Widget::new"
is called. In turn it calls "Tk::Text->DoInit($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 => $txtBg)" (note
lowercase). The result of the call is blessed into "Tk::Text", and
the method "bindtags" for this object is called.
Now the only thing to discuss is who defines the methods "text" and
"bindtags". The answer is that they are defined in "tkWindow.c", and
these commands are created in the package "Tk" in the same sweep
that created the command "Tk::wm" discussed above.
So the the same C code that corresponds to the processing of
corresponding TCL commands is called here as well (this time via
"XStoTk" interface).
Inside "$text->insert('insert','Hello, world!');"
As we discussed above, the subcommands of widget procedures
correspond to XSUB "XStoWidget". This XSUB substitutes the first
argument $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 v5.40.1 2025-04-13 Internals(3pm)
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