29 September 2004

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Ubuntu seems to have taken off very quickly since the preview release came out a few weeks ago. In general, people seem to like the small tweaks we’ve made to the default Gnome install. Of course, after the preview came out people found bugs in some of my Gnome patches …

One of the things we added was the trash applet on the panel. I made a fair number of fixes that make the applet fit in with the desktop a bit better and handle error conditions a bit better.

Probably the biggest fix was adding support for multiple trash directories. Originally the applet would move files to ~/.Trash and didn’t monitor any other trash directories, which meant that moving to the trash took longer than necessary on slow volumes and the applet didn’t correctly reflect the trash’s empty state if you used the “move to trash” context menu item in Nautilus.

One of the problems implementing this was that the trash handling in Gnome is pretty much entirely private to Nautilus. I managed to adapt the Nautilus code into a small class (about 500 lines) that could provide an item count for the trash, notification of changes to the item count, and the ability to empty the trash. A lot of the complexity in this code is to handle plugging and and unplugging of removable volumes. It’d be nice if this kind of code was available in gnome-vfs or something though.

Icon Theme APIs

While working on various Ubuntu fixes, I found an error that seems to be quite common in various bits of the desktop. It goes something like this:

  1. Find the image file for an icon at size n using gnome_icon_theme_lookup_icon() or gtk_icon_theme_lookup_icon().
  2. Create a GdkPixbuf from the image file using gdk_pixbuf_new_from_file().
  3. Use the pixbuf as an nxn icon.

The first problem with this is that gtk_icon_theme_lookup_icon() is not guaranteed to return an image at the desired size. This is quite obvious when you consider that you can pass in an arbitrary size to the lookup function, but the icon theme will only contain a finite number of sizes. However, if you ask for a common sized icon and the icon theme contains that size image, it might appear that the function will always return an image file of the requested size. The fix is to check the size of the loaded pixbuf and scale it if it is of the wrong dimensions.

The second problem is to do with SVG image files. They can be rendered at arbitrary sizes, but gdk_pixbuf_new_from_file() doesn’t tell the loader backend what size is actually wanted. This means that the SVG will be rendered at whatever size is listed in the file itself, which could be very large or very small. To avoid having to resize the SVG image after rendering it (which could be slow), you can use the gdk_pixbuf_new_from_file_at_size() routine (new in GTK 2.4) which passes the desired size to the backend so that ones like the SVG backend can render at an appropriate size. This function will return a pixbuf that fits into the bounding height/width you pass to it, and will perform scaling if the backend can’t load the image at the requested size.

If this sounds complicated, there is an easier way. You can just use gtk_icon_theme_load_icon(), which will lookup the image, and load it at the desired size all in one go. I guess there aren’t many people using it because there wasn’t an equivalent in the older GnomeIconTheme API.