Re: Finding width of a piece of text

[Behdad Esfahbod <behdad behdad org>]

On 04/26/2009 07:27 PM, Ian Puleston wrote:
> Hi,
>
> I'm having (yet another) problem with Pango. I have a need to find the width
> that a piece of text will be displayed. I thought this piece of code would
> do it, but the result is not quite right. The Pango attributes have been set
> for "Courier" font and point size 10:
>
>      lbl = gtk_label_new(pText);
>      gtk_label_set_attributes(GTK_LABEL(lbl), attrList);
>      layout = gtk_label_get_layout(GTK_LABEL(lbl));
>      g_assert(layout);
>      pango_layout_get_size(layout,&width,&height);
>
>      gdouble wid = (gdouble)width / (72 * PANGO_SCALE);
>      g_print("'%s' width %d units (%.2g\")\n", pText, width, wid);
>
> An example of what it prints is:
>
> 'Ken Hanlon' width 81920 units (1.1")
> 'Ian Puleston' width 98304 units (1.3")
>
> But those don't match the widths it prints on paper with the same font and
> point size - these names are both about 1" wide.

Why are you measuring a GtkLabel layout, but talk about print?  A GtkLabel is 
a widget to be shown on the screen.  Text metrics depend on the target surface 
(by way of surface font options).  Create a layout using 
pango_cairo_create_layout() directly for your target PDF/PS/etc surface.

behdad


> I also tried getting the PangoLayoutLine from the layout and using
> pango_layout_line_get_extents but got the same result.
>
> Note that the following code gets the width of a character from the font and
> reports it as 6074. Converting that from Pango units to points and then to
> inches works out at 0.988" for the above 12-digit strings, which looks
> exactly right. So why would this yield the correct width when
> pango_layout_get_size apparently does not?
>
>      ctx = pango_layout_get_context(layout);
>      g_assert(ctx);
>      fontDesc = pango_context_get_font_description(ctx);
>      g_assert(fontDesc);
>      lang = pango_context_get_language(ctx);
>      g_assert(lang);
>      metrics = pango_context_get_metrics(ctx, fontDesc, lang);
>      g_assert(metrics);
>      g_print("char width %d\n",
> pango_font_metrics_get_approximate_char_width(metrics));
>
> Ian
>
>
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