1Internals(3) User Contributed Perl Documentation Internals(3)
2
6 Tk::Internals - what is Perl Tk interface doing when you call Tk
7 functions.
8 This information is worse than useless for "perlTk" users, but can of
10 some help for people interested in using modified Tk source with
11 "perlTk".
12 This document is under construction. The information is believed to be
14 pertinent to the version of "portableTk" available when it was created.
15 All the details are subject to change.
16
18 PreCompiling
19 Before the actual compilation stage a script scans the source and
20 extracts the subcommands of different commands. This information
21 resides in the file "pTk/Methods.def".
22 Compilation
24 During compilation the above file is included in the source of
25 booting routine of dynamic (or static) library. More precisely, the
26 booting code of module "Tk" calls the subroutine Boot_Glue() from
27 the module "tkGlue.c", and this subroutine includes the file (with
28 appropriate macro definitions).
29 Inside "use Tk;"
31 The module bootstraps the C code, then loads the Perl libraries.
32 The heart of the Perl code is contained in the "Tk::Widget"
33 library, all the widgets inherit from this module. Code for
34 toplevels is loaded from "Tk::MainWindow".
35 During bootstrap of the C glue code the "Xevent::?" codes and a
37 handful of "Tk::Widget" and "Tk::Image" routines are defined. (Much
38 more XSUBs are created from "Tk.xs" code.) The widget subcommands
39 are glued to Perl basing on the list included from
40 "pTk/Methods.def". In fact all the subcommands are glued to XSUBs
41 that are related to the same C subroutine XStoWidget(), but have
42 different data parts.
43 During the Perl code bootstrap the method "Tk::Widget::import" is
45 called. This call requires all the code from particular widget
46 packages.
47 Code from the widget packages calls an obscure command like
49 (bless \"Text")->WidgetClass;
51 This command (actually Tk::Widget::WidgetClass()) creates three
53 routines: Tk::Widget::Text(), Tk::Widget::isText(), and
54 Tk::Text::isText(). The first one is basically "new" of "Tk::Text",
55 the other two return constants. It also puts the class into
56 depository.
57 Inside "$top = MainWindow->new;"
59 This is quite intuitive. This call goes direct to
60 "Tk::MainWindow::new", that calls XSUB
61 "Tk::MainWindow::CreateMainWindow", that calls C subroutine
62 Tk_CreateMainWindow(). It is a "Tk" subroutine, so here black magic
63 ends (almost).
64 The only remaining black magic is that the "Tk" initialization
66 routine creates a lot of commands, but the subroutine for creation
67 is usurped by portableTk and the commands are created in the
68 package "Tk". They are associated to XSUBs that are related to one
69 of three C subroutines XStoSubCmd(), XStoBind(), or XStoTk(), but
70 have different data parts.
71 The result of the call is blessed into "Tk::MainWindow", as it
73 should.
74 Inside "$top->title('Text demo');"
76 The package "Tk::Toplevel" defines a lot of subroutines on the fly
77 on some list. All the commands from the list are converted to the
78 corresponding subcommands of "wm" method of the widget. Here
79 subcommand is a command with some particular second argument (in
80 this case "title"). Recall that the first argument is $self.
81 Now "Tk::Toplevel" @ISA "Tk::Widget", that in turn @ISA "Tk". So a
83 call to "$top->wm('title','Text demo')" calls "Tk::wm", that is
84 defined during call to Tk_CreateMainWindow(). As it is described
85 above, the XSUB associated to XStoSubCmd() is called.
86 This C routine is defined in "tkGlue.c". It gets the data part of
88 XSUB, creates a "SV" with the name of the command, and calls
89 Call_Tk() with the XSUB data as the first argument, and with the
90 name of XSUB stuffed into the Perl stack in the place there "tk"
91 expects it. (In fact it can also reorder the arguments if it thinks
92 it is what you want).
93 The latter procedure extracts name of "tk" procedure and
95 "clientData" from the first argument and makes a call, using Perl
96 stack as "argv" for the procedure. A lot of black magic is
97 performed afterwards to convert result of the procedure to a Perl
98 array return.
99 Inside "$text = $top->Text(background => $txtBg);"
101 Above we discussed how the command "Tk::Widget::Text" is created.
102 The above command calls it via inheritance. It is translated to
103 Tk::Text::new($top, background => $txtBg);
105 The package "Tk::Text" has no method "new", so the
107 "Tk::Widget::new" is called. In turn it calls
108 "Tk::Text->DoInit($top)", that is
109 "Tk::Widget::DoInit(Tk::Text,$top)", that initializes the bindings
110 if necessary. Then it creates the name for the widget of the form
111 ".text0", and calls "Tk::text('.text0', background => $txtBg)"
112 (note lowercase). The result of the call is blessed into
113 "Tk::Text", and the method "bindtags" for this object is called.
114 Now the only thing to discuss is who defines the methods "text" and
116 "bindtags". The answer is that they are defined in "tkWindow.c",
117 and these commands are created in the package "Tk" in the same
118 sweep that created the command "Tk::wm" discussed above.
119 So the the same C code that corresponds to the processing of
121 corresponding TCL commands is called here as well (this time via
122 "XStoTk" interface).
123 Inside "$text->insert('insert','Hello, world!');"
125 As we discussed above, the subcommands of widget procedures
126 correspond to XSUB "XStoWidget". This XSUB substitutes the first
127 argument $text (that is a hash reference) to an appropriate value
128 from this hash, adds the additional argument after the first one
129 that contains the name of the subcommand extracted from the data
130 part of XSUB, and calls the corresponding Tk C subroutine via
131 "Call_Tk".
132 Ilya Zakharevich <ilya@math.ohio-state.edu>
134perl v5.34.0 2021-07-23 Internals(3)