C++ pango text orientation

Question

I'm trying to label the y-axis in a plot built using pango.

I'm unable to orient the text to run vertically up along the y-axis.

Relevant portion of code is:

 #include <gtkmm.h>

 Pango::FontDescription font;
 cr->save();  // where cr is Glib::RefPtr<Cairo::Context> const &
 cr->set_source_rgba(1.0,1.0,1.0,0.5);
 font.set_family("Monospace");
 font.set_style(Pango::STYLE_ITALIC);
 font.set_weight(Pango::WEIGHT_BOLD);
 font.set_absolute_size(20);
 Glib::RefPtr<Pango::Layout> x_axis_label = this->create_pango_layout("x-axis label");
 x_axis_label->set_font_description(font);
 cr->move_to(0.38,0.465);
 x_axis_label->show_in_cairo_context(cr);

 // so far so good, renders as expected

 // now trying to render the y-axis label
 Glib::RefPtr<Pango::Context> t_y_axis_label_ctxt = x_axis_label->get_context();
 Pango::Matrix p_matrix;
 // apply some transformation
 p_matrix.xx = 0.0;
 p_matrix.xy = 1.0;
 p_matrix.yx = 1.0;
 p_matrix.yy = 0.0;
 p_matrix.x0 = 0.0;
 p_matrix.y0 = 0.0;
 t_y_axis_label_ctxt->set_matrix(p_matrix);
 Glib::RefPtr<Pango::Layout> y_axis_label = Pango::Layout::create(t_y_axis_label_ctxt);

 y_axis_label->set_text("y-axis label"); // if this line of code is omitted I would expect, at least the text "x-axis label" to be rendered. But this does not happen.
 y_axis_label->set_font_description(font);
 cr->move_to(0.0,0.0);
 y_axis_label->show_in_cairo_context(cr);  // renders no output
 cr->restore();

I suspect the problem has something to do with context that i retrieve from x-axis label, and the expected copy behaviour is not manifesting.

Answer 1

Are you sure you want to rotate the Pango context? I believe that functionality was introduced in the pre-Cairo days; now you would just rotate the Cairo context, like:

cr->save();
cr->rotate_degrees(90);
Glib::RefPtr<Pango::Layout> y_axis_label = this->create_pango_layout("y-axis label");
y_axis_label->set_font_description(font);
cr->move_to(...); // wherever you wanna put it
y_axis_label->show_in_cairo_context(cr);
cr->restore();

If you still don't see anything, make sure you are not moving the label out of the visible area.