i press any key whether Escape or any other the program is hanging

It's not hanging, it's sleeping. Because you're asking it to sleep for 100 seconds after every key:

    # Avoid thrashing this procedure
    # Note Perl does not support usleep
    # For finer resolution sleep than seconds, try:
    #    'select undef, undef, undef, 0.1;'
    # to sleep for (at least) 0.1 seconds
    sleep(100);
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If you change that to 1, the "hanging" will go away. Better still would be to use Time::HiRes and usleep 100; which is probably what the author intended. Eg. Add

use OpenGL qw(:all);    # Use the OpenGL module
use strict;             # Use strict typechecking
use Time::HiRes qw[ usleep ];
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at the top and change to:

    # to sleep for (at least) 0.1 seconds
    usleep(100);
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