Re: gtk_icon_theme_load_icon and GDK_SCALE=2 results in blurry icon


On Tue, 2017-10-03 at 19:32 +0200, infirit wrote:
Op 10/03/2017 om 03:28 PM schreef Alexander Shaduri:

I have a HiDPI Screen with DPI set to 192, GDK_SCALE=2 and GDK_DPI_SCALE=-1.

I need to get an icon as a pixbuf for GtkIconView.

Short answer, there is no way to do scaling properly with pixbufs. The
only way I found to do this was setting icon names and using cairo surfaces.

Unfortunately, GtkIconView expects pixbufs in the model.
I don't see a way to pass cairo surfaces to it.

This is the code in gtkmm:
Glib::RefPtr<Gtk::IconTheme> default_icon_theme = Gtk::IconTheme::get_default();
Glib::RefPtr<Gdk::Pixbuf> icon = default_icon_theme->load_icon("drive-harddisk", 64, 

As others have mentioned use the _at_scale() version of the icon theme
functions, it handles all the necessary scaling for you. To get the
scale factor use gtk_widget_get_scale_factor on the window/widget.

Yes, tried that, GtkIconView scales the resulting pixbuf.

Another thing to think about is the quality of the icons. I added proper
scaling for a project and found that the a couple of png icons it used
where in only a single size and of low quality. No matter what you do in
this case there is no way to prevent blurry icons.

The quality is not an issue here. I can get a sharp 128-size icon when not
using GDK_SCALE=2.

Internally Gtk handles this transparently as long as use icon-names
instead of pixbufs. I highly recommend you use icon-names whenever
possible and use cairo surfaces if you need to draw over or transform
the icon.

I ended up using gtk_icon_theme_lookup_icon_for_scale and then retrieve
the surface at the very last moment with gtk_icon_info_load_surface.
gtk_icon_info_load_surface also sets the correct scaling factor on the
surface so there is no need to change it with
cairo_surface_set_device_scale. Most widgets will accept the surface
these days and you should start using them.

Not GtkIconView, it seems.

Is there a way to get a sharp icon with gtk_icon_theme_load_icon?

Yes I managed it as described above. I have a silly experiment in python
that uses cairo surfaces at [1], maybe this helps. The moment you write
to png and use it as source on a widget things go blurry.



I'm at loss here, I guess this can be viewed as a bug in GtkIconView.


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