Gtk3 TextView modifying font size and keeping the current visible text on screen - gtk3

Question

I'm working with a Textview widget and I can modify the font-size of the Textview widget with the Ctrl key + mouse scroll wheel but my displayed text scrolls when I do it.... How do I keep the current text from scrolling up or down while I modify the font size of the Textview widget?
A few notable things about the code. The font-size is changed via styles and provider because I can't figure out how to get Pango to work with a TextView widget. I hardwired the code to retrieve some data from my $str = qx(perldoc -T -t -f split 2>&1)... You'll probably have to change this to your own data source.
#! /usr/bin/env perl
use feature qw(state);
use warnings;
use strict;
use utf8;
use CSS::Tiny;
use constant FONT_UNIT => 4;
use constant MAX_FONT_SIZE => 200;
use constant MIN_FONT_SIZE => 12;
use Glib qw(TRUE FALSE);
use Gtk3 qw(init);
sub killKey {
my ($object, $event) = #_;
my $c = lc chr ($event->keyval);
Gtk3->main_quit if $c eq 'q';
FALSE;
}
sub changeFontSize {
my ($font_size, $amount) = #_;
$font_size += $amount;
$font_size .= "px";
$font_size;
}
sub changeStyle {
my ($css, $provider, $style) = #_;
$style->remove_provider($provider);
$provider->load_from_data($css->write_string);
$style->add_provider(
$provider,
Gtk3::STYLE_PROVIDER_PRIORITY_APPLICATION
);
}
sub catchScroll {
my ($object, $event, $data) = #_;
my ($css, $provider, $style) = #{$data};
my $dir = $event->direction;
my ($ctrl, $mod) = #{$event->state};
my $font_size = $css->{textview}->{q<font-size>};
{
no warnings qw<numeric>;
$font_size += 0;
}
if ($ctrl eq q<control-mask> && $mod eq q<mod2-mask>) {
if ($dir eq q<up>) {
$css->{textview}->{q<font-size>} =
changeFontSize($font_size, FONT_UNIT)
if $font_size < MAX_FONT_SIZE;
}else{
$css->{textview}->{q<font-size>} =
changeFontSize($font_size, -FONT_UNIT)
if $font_size > MIN_FONT_SIZE;
}
changeStyle($css, $provider, $style);
}
FALSE;
}
my $window = Gtk3::Window->new(q<toplevel>);
my $scrWin = Gtk3::ScrolledWindow->new();
my $tView = Gtk3::TextView->new();
my $provider = Gtk3::CssProvider->new();
$provider->load_from_path("the.css");
my $style = $tView->get_style_context();
$style->add_provider($provider, Gtk3::STYLE_PROVIDER_PRIORITY_APPLICATION);
my $css = CSS::Tiny->read_string($provider->to_string);
#hardwired data for the TextView
my $str = qx(perldoc -T -t -f split 2>&1);
my $buf = $tView->get_buffer();
$buf->set_text($str);
my $sIter = $buf->get_start_iter();
$buf->place_cursor($sIter);
$tView->set_editable(FALSE);
$window->add_events(q<GDK_KEY_PRESS_MASK>);
$window->add_events(q<GDK_SCROLL_MASK>);
$window->signal_connect(delete_event => sub{Gtk3->main_quit; FALSE});
$window->signal_connect(key_press_event => \&killKey);
$window->signal_connect(
scroll_event =>
\&catchScroll,
[$css, $provider, $style]
);
$window->set_decorated(FALSE);
$window->set_position(q<center>);
$window->fullscreen;
$scrWin->add($tView);
$window->add($scrWin);
$window->show_all;
Gtk3::main;
the.css
text {
background-color: rgb(0,0,0);
color: rgb(0,255,0);
}
textview {
font-size: 40px;
}