Re: Gtk::Image and HiDPI

[Kasper Peeters <kasper peeters phi-sci com>]

> Try using a Cairo surface (or cairo_surface_t) with the appropriate
> scaling factor (see cairo_surface_set_device_scale).
>
> A GdkPixbuf doesn't have a scaling factor attached to it, but a Cairo
> surface does. Generally speaking, these days there's a trend to move
> towards the latter wherever possible and makes sense.

I tried using a Gtk::DrawingArea instead of my Gtk::Image, and then used
the following override of 'DrawingArea::on_draw' to draw my pixbuf onto
the Cairo surface provided by the DrawingArea:

-----
bool MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr)
   { 
   if(!pixbuf) return false;

   auto surface = cr->get_target();
   auto csurface = surface->cobj();
   cairo_surface_set_device_scale(csurface, 1.0, 1.0);
   Gdk::Cairo::set_source_pixbuf(cr, pixbuf, 0, 0);
   cr->paint();
   }
-----

Unfortunately, the inclusion of that 'cairo_surface_set_device_scale'
makes the widget go black completely, unless the scale factor already
was 1.0. 

So this is probably not what you meant... Can you give me a pointer?

Thanks,
Kasper