Re: [cairo] Writing a PangoLayoutLine on a line in cairo



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 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






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