227. How to set the tab position for GtkTextView - Part 2 - at every 4th character?

Problem

By default, GtkTreeView sets the tab at every eighth character as shown below:

Suppose you would like to set the tab position at every fourth character instead as shown below:

How to set the tab position for GtkTextView - Part 2 - at every 4th character?


Solution

  • Create a new PangoTabArray on the GtkTreeView.
  • Calculate the width of the font. With this information, we can calculate the width in pixels for every fourth character.
  • Set each tab position with PangoTabArray::set_tab()
  • Then impose the tabs on the textview with GtkTextView::set_tabs() on the GtkTreeView.

Sample Code

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<?php
$window = new GtkWindow();
$window->set_size_request(400, 240);
$window->connect_simple('destroy', array('Gtk','main_quit'));
$window->add($vbox = new GtkVBox());

// display title
$title = new GtkLabel("Set the Tab Position of GtkTextView\n".
"Part 2 - at every 4th character");
$title->modify_font(new PangoFontDescription("Times New Roman Italic 10"));
$title->modify_fg(Gtk::STATE_NORMAL, GdkColor::parse("#0000ff"));
$title->set_size_request(-1, 40);
$title->set_justify(Gtk::JUSTIFY_CENTER);
$alignment = new GtkAlignment(0.5, 0, 0, 0);
$alignment->add($title);
$vbox->pack_start($alignment, 0, 0);
$vbox->pack_start(new GtkLabel(), 0, 0);

// Create a new buffer and a new view to show the buffer.
$buffer = new GtkTextBuffer();
$view = new GtkTextView();
$view->set_buffer($buffer);
$view->modify_font(new PangoFontDescription("Courier New 16")); // note 6
$view->set_wrap_mode(Gtk::WRAP_WORD);
$buffer->set_text("123456781234567812345678\n");

$scrolled_win = new GtkScrolledWindow();
$scrolled_win->set_policy( Gtk::POLICY_AUTOMATIC, Gtk::POLICY_AUTOMATIC);
$vbox->pack_start($scrolled_win);
$scrolled_win->add($view);

$window->show_all();

$style = $view->get_style();
$font = $view->get_style()->font_desc;
$font_size_in_pango_unit = $font->get_size(); // note 1
$font_size_in_pixel = $font_size_in_pango_unit/1024; // note 2

$tabs = new PangoTabArray(0, true);
$index = 0;
for ($i=0; $i<400; $i=$i+$font_size_in_pixel*4) { // note 3
    $tabs->set_tab($index, PANGO::TAB_LEFT, $i); // note 4
    ++$index;
    print "pos $index: $i\n";
}
$view->set_tabs($tabs); // note 5

Gtk::main();

?>

Output

As shown above.

 

Explanation

  1. Get the font size. Note that this is in pango unit.
  2. Convert from pango unit to pixels.
  3. Note that we are using fixed-width font here. So we simply multiply the font width by 4.
  4. Set the tab positions. In this example, we set a tab for every 100 pixels.
  5. Set the tab on the treeview.
  6. Try changing this to other font size. You will see that the tab will always be set at every fourth character.

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