Sample Code 420: How to place a background image in GtkWindow - Part 5 - align top left - using GdkDrawable draw_pixbuf? |
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Written by kksou
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Thursday, 24 January 2008 |
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Problem This is in response to Andreas' Post titled "Possible to add not tiled backgrounds".
Suppose you want to have a single background image that always stayed at the top left corner of a GtkWindow (no matter how the user changes the window size) as shown below.
This article presents a more advanced and flexible solution that uses GdkDrawable::draw_pixbuf().
Solution
- The concept is actually very simple: get the underlying GdkWindow (which is a subclass of GdkDrawable), and then draw the background image directly onto this GdkWindow!
- However, for those we have tried this method before, the most challenging part is where do you put this piece of code — to have the background image shown, and yet without any program error!
- It took me a couple of days of trials and errors to get this working! It's in the callback function of the expose-event!
- I thought getting the GdkDrawable and GdkGC would be complicated. Take a look at the solution below. You'll be surprised how simple the solution turns out to be!
Sample Code Note: The following image file is required by the sample code below. Please save a copy of the image files and put them in the same directory where you store the sample code.
 | sample6_150a.png |
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| <?php
$window = new GtkWindow();
$window->set_size_request(480, 240);
$window->connect_simple('destroy', array('Gtk','main_quit'));
$window->add($vbox = new GtkVBox());
// display title
$title = new GtkLabel(
" Place a background image in GtkWindow\n".
"Part 5 - align top left - using GdkDrawable::draw_pixbuf()");
$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);
$vbox->pack_start($title, 0);
$vbox->pack_start(new GtkLabel(), 0);
$vbox->pack_start(new GtkLabel("Try enlarge the window."));
$vbox->pack_start(new GtkLabel("There's only one image."));
$vbox->pack_start(new GtkLabel(
"And the background image stays at the same place!"));
// set background image
/*$pixbuf=GdkPixbuf::new_from_file("sample6_1920_br.png");
list($pixmap,$mask)=$pixbuf-> render_pixmap_and_mask(255);
$style = $window->get_style();
$style=$style->copy();
$style->bg_pixmap[Gtk::STATE_NORMAL]=$pixmap;
$window->set_style($style);*/
$window->connect('expose_event', 'expose_event'); // note 1
$window->show_all();
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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
- Register for the signal 'expose_event'.
- Load the background image. This works with all standard image file format such as .gif, .jpg or .png.
- Surprised by this one-liner?! Yes, this is the line that sets the background image! I was quite surprised that this even works for the alpha/Gnope version!
Note
Try compare this method with that described in How to place a background image in GtkWindow - Part 3 - align top left - using GtkStyle? and you'll understand why this method is more advanced and seemingly "better":
- Did you notice that this method supports transparencies in .png and .gif file?
- As we're drawing each image directly onto the underlying GdkWindow, there's no issue of tiled images.
- You can use the image file as-is. When using the GtkStyle method, you have to "pad" the image to 1920x1200.
- You can position the image to the exact location you want, as we shall see in the next article.
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