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Problem This is in response to Paamayim's post titled 'smooth scrolling for a gtkimage drawing'.
He has set up a bar graph and wants to allow the user to dynamically change the scale of the x-axis and y-axis through the scrollbars as shown below.
As there are quite a number of techniques involved, to make it easier to follow, I've spread the techniques over 5 parts:
- Part 1 - adds the vscrollbar
- Part 2 - aligns the graph to bottom left
- Part 3 (this article) - adds the hscrollbar
- Part 4 - adds both vscrollbar and hscrollbar
- Part 5 - use only one scrollbar to control scaling of both axis
In this Part 3, we will setup a hscrollbar for scaling the x-axis as shown below:
Solution
- Setting up the hscrollbar is very similar to setting up a vscrollbar as outlined in Part 1.
- The only difference is that instead of using the GtkVscrollbar, we use the GtkHscrollbar.
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$window = new GtkWindow();
$window->set_title($argv[0]);
$window->connect_simple('destroy', array('Gtk','main_quit'));
$window->add($vbox = new GtkVBox());
// display title
$title = new GtkLabel("Dynamically scale a bar graph using scrollbars\n".
"Part 3: x-direction only with hscrollbar");
$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);
$vbox->pack_start(new GtkLabel(), 0, 0);
setup_bargraph($vbox);
$window->show_all();
Gtk::main();
function setup_bargraph($vbox) {
global $img;
$vbox->pack_start($vbox2 = new GtkVBox());
$img = new GtkImage();
$vbox2->pack_start(new GtkVBox());
$vbox2->pack_start($hbox2 = new GtkHBox(), 0);
$hbox2->pack_start($img, 0);
$adj = new GtkAdjustment(0.5, 0.5, 2, 0.01, .5); // note 1
$hscrollbar = new GtkHScrollbar($adj); // note 2
$hscrollbar->connect('value-changed', 'on_value_changed'); // note 3
$vbox->pack_start($hscrollbar, 0);
$adj->set_value(1); // note 4
$adj->value_changed();
$vbox2->set_size_request(600, 210);
}
function draw_bargraph($x_scale, $y_scale) {
global $img;
$max_width = 360 * $x_scale;
$max_height = 200 * $y_scale;
$margin = 40;
$im = imagecreate($max_width, $max_height);
$white = imagecolorallocate($im,255,255,255);
$black = imagecolorallocate($im,0,0,0);
$blue = imagecolorallocate($im,0,0,255);
$data = array('120','160','300','240');
imageline($im, 10, 5, 10, $max_height-$margin, $black );
imageline($im, 10, $max_height-$margin,
$max_width-$margin, $max_height-$margin, $black );
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- Note that this is only 70% of the sample code. You have to be a registered member to see the entire sample code. Please login or register.
- Registration is free and immediate.
- Have some doubt about the registration? Please read this forum article.
Explanation The above code is very similar to that of Part 2. What's new here:
- Create the GtkAdjustment.
- Create the hscrollbar and binds the GtkAdjustment to the scrollbar.
- Register for the signal
value-changed.
- Set the initial value to 1.
- Get the current value of the Gtkadjustment/scrollbar.
- Redraw the bar graph.
Note
This example serves mainly to illustrate the use of GtkAdjustment and GtkVScrollbar. I will leave it to you to optimize and polish the gd2 portion (for the display of the bar graph).
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