[Solved?] How to convert from Gtk::FontButton to Cairo::Context::select_font_face / set_font_size?

Platform
1

I can pick fonts easily with Gtk::FontButton, but fonts are returned as a string (glib::ustring).

How can this font be used, then, in a Cairo::Context ? It does not have any function to provide this string. Instead, it wants independent parameters for font name, style and size.

I tried looking for this as best as possible, but I can’t find any method to convert from one format to the other.

2

I have the feeling this would help but it seems broken:

https://developer.gnome.org/pangomm/unstable/classPango_1_1FontDescription.html

3

Nope, I can’t seem to use pango for this, I Can’t get the font size reliably from FontDescription… how is this done properly? Nothing in these APIs makes any sense.

4

The documentation in fontdescription.h in pangomm is very confusing, the one in pygtk is different and better, I had to divide the size by Pango::SCALE… so not quite sure if it’s right. It works, though.

5

GtkFontButton implements the GtkFontChooser interface, which contains a GtkFontChooser::font-desc property. But note that font descriptions, by nature, don’t contain every aspect of a font. See pango_font_description_get_set_fields() for the bit-mask of what has been set.

Some of that data can’t be “resolved” until the font is used in context, so that a font map can be applied as well as other display specific conditions.

To use the PangoFontDescription with cairo, you can use a PangoLayout. If you are are rendering to a GTK widget, gtk_widget_create_pango_layout() will get you one. If you are using cairo only, pango_cairo_create_layout() can be used with your cairo_t.

A quick example:

PangoFontDescription *font_desc = gtk_font_chooser_get_font_desc (GTK_FONT_CHOOSER (button));
PangoLayout *l = gtk_widget_create_pango_layout (GTK_WIDGET (self));
pango_layout_set_font_description (l, font_desc);
pango_layout_set_text (l, "Foo", -1);
pango_cairo_show_layout (cr, l);
g_object_unref (l);
g_object_unref (font_desc);
6

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