RE: Finding width of a piece of text

["Ian Puleston" <ian underpressuredivers com>]

> -----Original Message-----
> From: Behdad Esfahbod 
> 
> On 05/20/2009 06:38 PM, Ian Puleston wrote:
> >> -----Original Message-----
> >> From: Ian Puleston
> >> Sent: Sunday, April 26, 2009 8:31 PM
> >>
> >>> -----Original Message-----
> >>> From:>  Behdad Esfahbod
> >>> Sent: Sunday, April 26, 2009 6:13 PM
> >>>
> >>> On 04/26/2009 07:27 PM, Ian Puleston wrote:
> >>>> with Pango I have a need to find the width that a piece of
> >>>> text will be displayed.
> >>>>
> >>>> I can't use pango_cairo_create_layout() at this point because I
> >>>> don't yet know what print device it will be printed on.
> >>> Then at least 1) make sure your context is set to 72 dpi, and 2)
> set
> >>> font options to disable metrics hinting.
> 
> I already told you what you need to do.
> 
> behdad

I think that I am doing everything that you suggested in the function below, but it is not producing quite the correct result. Do you see something that you suggest which is missing from it?

> 
> >>> behdad
> >> I added a call to pango_cairo_context_set_resolution(ctx, 72) and
> that
> >> fixed it.
> >
> > Well it nearly fixed it. I'm using this to truncate text to fit into
> fixed
> > width columns when it is printed, and although its generally working
> well
> > I've noticed that some text is getting truncated when it doesn't
> quite need
> > to be. So I added some debug printing of the text width and it is not
> being
> > reported quite the same as the width that the text is printed.
> >
> > The function that I wrote to get the text width is below. For the
> text "Ian
> > Puleston" with Arial font and point size 10 it returns width 60416
> Pango
> > units which translates to 0.82" (60416 / 1024 / 72), but when that is
> > printed the name takes just about exactly 0.75" width.
> >
> > So anyone got any idea what may be wrong with the following code to
> cause
> > that?
> >
> >
> >
> /*=====================================================================
> =====
> > ==*/
> > /*
> >   * This calculates the width that some given text will be when
> printed.
> >   */
> > int
> > getPrintWidth(const char *pText, PangoAttrList *textAttrs)
> > {
> >      GtkWidget               *lbl;
> >      PangoAttrList           *attrList;
> >      PangoLayout             *layout;
> >      PangoContext            *ctx;
> >      cairo_font_options_t    *fontOpts;
> >      int                     width, height;
> >
> >      /* We can find the size by putting the text into a label widget,
> setting
> >       * the resolution of that widget to 72dpi (dot == point) and
> querying
> > the
> >       * width of the resulting layout */
> >      lbl = gtk_label_new(pText);
> >      attrList = pango_attr_list_copy(textAttrs);
> >      g_assert(attrList);
> >      gtk_label_set_attributes(GTK_LABEL(lbl), attrList);
> >      layout = gtk_label_get_layout(GTK_LABEL(lbl));
> >      g_assert(layout);
> >
> >      /* To get the correct text width we need to make sure the label
> we put
> >       * it in has a resolution of 72dpi (a dot is equivalent to a
> text point)
> > */
> >      ctx = pango_layout_get_context(layout);
> >      g_assert(ctx);
> >      pango_cairo_context_set_resolution(ctx, 72);
> >
> >      /* This next probably isn't needed but to make sure font size is
> > consistent
> >       * we turn off font metrics hinting (to do with constant font
> size on
> > zoom) */
> >      fontOpts = cairo_font_options_create();
> >      cairo_font_options_set_hint_metrics(fontOpts,
> CAIRO_HINT_METRICS_OFF);
> >      pango_cairo_context_set_font_options(ctx, fontOpts);
> >
> >      pango_layout_get_size(layout,&width,&height);
> >
> >      gtk_widget_destroy(lbl);
> >      pango_attr_list_unref(attrList);
> >      cairo_font_options_destroy(fontOpts);
> >
> >      g_print("'%s' width %d\n", pText, width);
> >
> >      return (width);
> > }
> >
> >
> >
> >
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