[cairo] Writing a PangoLayoutLine on a line in cairo

[Dov Grobgeld]

I'm not sure that depth is a good name as it according to the MetaFont
book page 101 describes the distance from the baseline of a character
to the bottom of the character bounding box. Since both pango and
cairo work in a top-bottom coordinate system, the depth is usually not
what is needed but rather  the "distance_from_top_of_the
logical_rect_to_baseline" but that is a bit long to type. Perhaps just
"get_top_baseline_pos":

/**
 * Returns the "baseline" of a layout, that is the distance from the
 * top of the layout to the baseline of the first line in the
 * layout.
  */
int pango_layout_get_top_baseline_pos(PangoLayout *layout)
{
  PangoLayoutLine *layout_line = pango_layout_get_line(layout,0);
  PangoRectangle rect;

  pango_layout_line_get_extents(layout_line,
                                NULL,
                                &rect);

  return PANGO_ASCENT(rect);
}

The terminology is problematic for vertical layouts though...

Regards,
Dov
On 2/3/07, Owen Taylor <otaylor at redhat.com> wrote:
> On Sat, 2007-02-03 at 21:48 +0200, Dov Grobgeld wrote:
> > I
> > In pango_cairo_show_layout() on the other hand, the layout logical
> > upper left corner is aligned at the current cairo point when drawing,
> > and I could not find any PangoLayout call that gets the distance from
> > the top of the logical rectangle to the baseline position. Is this a
> > bug, or did I miss something?
>
> Well, one easy way to do it is to just draw the first line of the
> layout instead of the entire layout - since the y origin when drawing a
> single line is at the baseline of the line.
>
>  PangoLayoutLine *line = pango_layout_get_lines(layout)->data;
>  pango_show_layout_line(cr, line);
>
> If you want to draw an entire layout with the first line positioned
> at a particular y position, then you'd need to get the ascent of the
> first line:
>
>  PangoRectangle rect;
>  pango_layout_line_get_extents(line, NULL, &rect);
>  double ascent = (double)PANGO_ASCENT(rect) / PANGO_SCALE;
>
> It might be handy to have a convenience function to get this -
> pango_layout_get_depth(), say, to steal terminology from TeX.
>
>                                         - Owen
>
>
>