Why can't you pass the coordinates to sub C?

And do you call sub B, or does sub C call sub B? I think I'm distilling the notion that you want C to call B, am I right? Let's roll with that.

Why would this not work for you?

sub subA {
    # ...
    # generate array;
    # here be dragons, an' arrays an' pushes an' references
    # an' lots of dereferencing happens here, me lad.
    # ...    
    return \@array;
}

sub subB {
    my $chart_widget = shift;
    my $data_aref    = shift;

    $chart_widget->chart( $data_aref ) # or however Tk::Chart be used,
+ matey
}

sub subC {
    my $chart_widget = shift;
    my $data_aref    = shift;
    
    # ...
    # I don't have a clue what be happenin' here, me hearty.
    # ...

    subB($chart_widget, $data_aref);
}
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And from your main code:

my $chart = $mw->Chart( ... );

my $data_aref = subA;
subC($chart, $data_aref);
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