How to set line height in Clutter.Text using Pango - gtk

Question

I want to have a Clutter.Text displaying text with double line spacing using Gtk.Pango.
note : in css, we would use line-height: 200% I think.
I tried this code and it didn't work:
var text_actor = new Clutter.Text.with_text ("Roboto 10", "Long long text") ;
text_actor.width= SIDE_PANE_WIDTH ;
text_actor.get_layout ().set_spacing (2*Pango.SCALE) ;
Apparently, Clutter.Text keeps a cached version of the Pango.Layout
Is there a way to achieve this?

Answer 1

One way working around this by using CoglPango directly:
var t = new Clutter.Actor ();
t.set_size (300, 300);
// add some more text to see it
var text = "Lorem ipsum dolor sit amet, consectetur adipisicing elit, ...";
var layout = t.create_pango_layout (text);
layout.set_width (200);
layout.set_spacing (24 * Pango.SCALE);
t.paint.connect (() => {
Cogl.pango_render_layout (layout, 0, 0,
Cogl.Color.from_4ub(0, 0, 0, 255), 0);
});
edit this is indeed the solution. Based on this, here's the code that I used:
actor = new Text () ;
actor.width= SIDE_PANE_WIDTH ;
var text = "Some long text<b>Bold</b>" ;
var pango_layout = bio_actor.create_pango_layout ("");
pango_layout.set_markup (text, text.length) ;
pango_layout.set_spacing (2 * Pango.SCALE);
pango_layout.set_font_description (Pango.FontDescription.from_string ("Roboto 10")) ;
pango_layout.set_width (SIDE_PANE_WIDTH * Pango.SCALE);
bio_actor.paint.connect (() => {
Cogl.pango_render_layout (pango_layout, 0, 0, Cogl.Color.from_4ub(255, 255, 255, 255), 0);
});
int width;
int height ;
pango_layout.get_size (out width, out height) ;
actor.height = height / Pango.SCALE;

Answer 2

Yes, ClutterText caches the PangoLayout instance to avoid having to re-measure text every time it has to retrieve the preferred size. It actually caches the latest three instances of PangoLayout, because of the width-for-height/height-for-width geometry requests, but that's just an implementation detail.
Changing properties on the PangoLayout instance of ClutterText is also not going to result in updates to the ClutterText: you'd have to call clutter_actor_queue_redraw() afterwards, as the PangoLayout sits at a lower level than the actor in the scene graph.
In general, the ClutterText actor does not allow you to tweak the PangoLayout it creates; it's expected that the actor is in charge of creating an modifying the layout, and attempts at overriding that will result in either poor performance or undefined behaviour.
If you want to introduce a line spacing property then you'll have to file a bug against ClutterText — though that would mean that you'd have to wait until September for the next stable release of Clutter.
If you don't need all that ClutterText does, and you just want to display text, you could subclass ClutterActor and use clutter_actor_create_pango_layout() to create a PangoLayout that you can measure inside the overridden get_preferred_width(), get_preferred_height(), and allocate() virtual functions, and paint inside the overridden paint() virtual function.