How Not to Port Tk::Square (Mastering Perl/Tk)

21.4. How Not to Port Tk::Square

As we learned earlier, it's best to keep private C widgets distinct from the Perl/Tk distribution. But if we were to do a merge, here are some considerations.

First, copy tkSquare.c (with the same hand edits described previously) to pTk/mTk/generic, copy square_demo.t to t, and then fire up your favorite editor and add these lines to the main Perl/Tk MANIFEST:

Square/Makefile.PL
Square/Square.xs 
Square/Square.pm
pTk/mTk/generic/tkSquare.c
t/square_demo.t

Now make the Square directory and populate it with the preceding files. The files Square.xs and Square.pm are the exact same files we just used, but Makefile.PL looks like this:

use Tk::MMutil;
Tk::MMutil::TkExtMakefile(
    'dynamic_ptk' => 1
);

Secondly, we must add a single statement to three files so the Perl/Tk core is "aware of" Tk_SquareCmd.

To pTk/mTk/generic/tk.h, add the followingaround line 1880:

EXTERN int Tk_SquareCmd _ANSI_ARGS_((ClientData clientData,
        Tcl_Interp *interp, int argc, char **argv));

To pTk/mTk/generic/tkWindow.c, add the following around line 152:

{"square",        Tk_SquareCmd,         NULL,              1},

To pTk/tk.exc,add the following around line 96:

Tk_SquareCmd

It may be advisable to start fresh and begin with:

make distclean
perl Makefile.PL

Making and testing the widget code is similar to what we just did, although development is slower because it's a make from the top of the entire Perl/Tk hierarchy, with scores of dependencies and nested makes. You'll quickly find that the make; make test cycle is ridiculously slow.

Testing is sped up if we use a command of the form:

perl -Mblib Square/t/square_demo.t

This uses all the newly made code (both Perl and the loadable object) from blib, the build library.

We can even fake a make install with a script that might look like this (although the exact pathnames vary):

#!/bin/sh
make
cp blib/arch/auto/Tk/Square/Square.so /usr/local/lib/perl5/site_perl/5.005/i686-
linux/auto/Tk/Square/Square.so

Of course, this only "installs" the C loadable, not the .pm file or autosplit subroutines.

There are various techniques for debugging the C code, but perhaps the easiest is the tried-and-true fprintf statement (don't forget the #include <stdio.h>):

fprintf(stderr, "square size=%d\n", squarePtr->size);