Supporting UI Scaling
GTK3 and above support integer scaling of UI components, most useful on HiDPI screens. In Xfce, this can be set in the Appearance settings panel. GTK3 will handle drawing widgets and windows at the new scale automatically, but care has to be taken to supply it with images and icons properly in order for them to be displayed at the correct resolution, without being blurry.
gtk_widget_get_scale_factor()to get the scale factor.
- If you don't have a widget handy, but for some reason have a
GdkWindow, you can use
- If you don't even have a window, you can use
- Scale factors are (unfortunately) integer-only. There's no such thing as a 1.5x scale, for example.
- You can connect to
GdkMonitorinstance to know when you might need to reload icons at a new scale factor.
Things that work
- Any manually-loaded
GdkPixbufinstances should be loaded at a width and height multiplied by the scale factor. Then, “wrap” the pixbuf in a
gdk_cairo_surface_create_from_pixbuf(), which takes the scale factor. It can also take a
GdkWindow, but it's fine to pass
- When loading themed icons, use the
gtk_icon_theme_lookup_by_gicon_for_scale(). Pass the unscaled size for the
sizeparameter, and the UI scale factor for the
scaleparameter. I also recommend passing
GIconis a useful alternative in cases where it's awkward to pass around a scale factor (for example, in a
GtkTreeModelimplementation, the model shouldn't really know “view” details like the UI scale factor).
GIconhas quite a few implementation types, like
GIcon. There's also
GLoadableIcon, which you can fairly easily implement if you need to do something custom.
- If using
GtkImage, you can get arbitrary sizing (that is, other sizes beyond what
GTK_ICON_SIZE_offers) by using
gtk_image_set_pixel_size(). The code in
GTK_ICON_SIZE_sizes if the pixel size is specified. For the pixel size, you want to specify the unscaled size.
- Most things that take a themed icon name will automatically handle the scale factor internally.
- Many things that take
GdkPixbufwill also take
cairo_surface_t, so look for another function variant when replacing existing calls.
Things that are problematic
GdkPixbufinstances manually will result in blurry icons without specifically handling the scale factor.
GtkCellRendererPixbufwork ok if you are only using “standard” GTK icon sizes (that is, the
GTK_ICON_SIZE_enum values). That should usually be fine for things like
GtkTreeView, but might not work well for
GtkIconView, as those size types max out at 48×48.
- Don't try to “outsmart”
GtkIconThemeby writing your own size selection and loading code.
GtkIconThemewill nearly always do the right thing, and handles a lot of the complex rules that can be encoded into an
index.themefile. Working around this can give results that aren't true to what the icon theme authors intended.