Re: pango_layout_set_width() versus measured widths

[Behdad Esfahbod <behdad behdad org>]

I've now pushed a fix to pango master.  I'll put in the next stable release 
also if/when that happens.


http://git.gnome.org/browse/pango/commit/?id=2cd9c4b416cbe55dd68106003f360e861a6722be


Thanks,
behdad

On 12/22/2009 11:13 PM, Ben Pfaff wrote:
> In working with Pango I found an oddity that I do not understand.
> It may be a bug, or it might just be my misunderstanding.
>
> As part of a table layout procedure for printing, my code wishes
> to find out the width of the longest word in a Pango layout, so
> it sets the width of the layout to 1, turns on word wrapping, and
> measures the width of the layout, something like this:
>
>          pango_layout_set_width (layout, 1);
>          pango_layout_set_wrap (layout, PANGO_WRAP_WORD);
>          pango_layout_get_size (layout,&width, NULL);
>
> Later on, the width of the table column might have been adjusted
> upward or downward for other reasons, so it renders it with
> PANGO_WRAP_WORD_CHAR to prevent overflowing the column
> boundary.  I was surprised to discover that, when the layout
> width is set to the same value returned by
> pango_layout_get_size(), this caused some words to wrap anyhow.
>
> I'm enclosing a simple example program.  You can invoke it to
> measure the size of rendering "A string of text" with a width of
> 1 and word-wrapping, as above, e.g. showing input, output, and
> an ASCII rendering of the produced foo.pdf:
>
>          # ./a.out "A string of text" 1 word
>          size: width=47032
>          extents: ink width=45416, logical width=47032
>          pixel extents: ink width=45, logical width=46
>
>          +------+
>          |A     |
>          |string|
>          |of    |
>          |text  |
>          +------+
>
> Then giving the exact width reported by this run, plus word-char,
> yields:
>
>          # ./a.out "A string of text" 47032 word-char
>          size: width=36632
>          extents: ink width=35112, logical width=36632
>          pixel extents: ink width=35, logical width=36
>
>          +-----+
>          |A    |
>          |strin|
>          |g of |
>          |text |
>          +-----+
>
> To get word-char to produce the results that I expect, I have to
> add 5208, which is the reported width of " ":
>
>          # ./a.out "A string of text" 52240 word-char
>          size: width=47032
>          extents: ink width=45416, logical width=47032
>          pixel extents: ink width=45, logical width=46
>
>          +------+
>          |A     |
>          |string|
>          |of    |
>          |text  |
>          +------+
>
> Any guidance would be appreciated.  I can always add the width of
> a space myself, but I don't understand why it is necessary.
>
> Here is my test program:
>
> #include<pango/pangocairo.h>
> #include<cairo/cairo-pdf.h>
> #include<cairo/cairo.h>
> #include<stdlib.h>
> #include<string.h>
>
> int
> main (int argc, char **argv)
> {
>    cairo_t *cr;
>    char *filename;
>    cairo_status_t status;
>    cairo_surface_t *surface;
>    PangoLayout *layout;
>    PangoFontDescription *desc;
>    PangoRectangle ink, logical;
>    int width;
>
>    if (argc != 4)
>      {
>        g_printerr ("Usage: pangocairo STRING WIDTH WRAP_MODE\n");
>        return 1;
>      }
>
>    /* Create surface and clear to all-white. */
>    surface = cairo_pdf_surface_create ("foo.pdf", 200, 200);
>    cr = cairo_create (surface);
>    cairo_set_source_rgb (cr, 1.0, 1.0, 1.0);
>    cairo_paint (cr);
>
>    /* Create Pango layout. */
>    layout = pango_cairo_create_layout (cr);
>    desc = pango_font_description_from_string ("Sans 12");
>    pango_layout_set_font_description (layout, desc);
>    pango_font_description_free (desc);
>    pango_layout_set_text (layout, argv[1], -1);
>
>    /* Set Pango options according to command line. */
>    pango_layout_set_width (layout, atoi (argv[2]));
>    if (!strcmp (argv[3], "word"))
>      pango_layout_set_wrap (layout, PANGO_WRAP_WORD);
>    else if (!strcmp (argv[3], "char"))
>      pango_layout_set_wrap (layout, PANGO_WRAP_CHAR);
>    else if (!strcmp (argv[3], "word-char"))
>      pango_layout_set_wrap (layout, PANGO_WRAP_WORD_CHAR);
>    else
>      {
>        g_printerr ("WRAP_MODE must be 'word' or 'char' or 'word-char'");
>        return 1;
>      }
>
>    /* Draw layout. */
>    cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
>    cairo_move_to (cr, 0, 0);
>    pango_cairo_show_layout (cr, layout);
>
>    /* Print various sizes. */
>    pango_layout_get_size (layout,&width, NULL);
>    printf ("size: width=%d\n", width);
>
>    pango_layout_get_extents (layout,&ink,&logical);
>    printf ("extents: ink width=%d, logical width=%d\n",
>            ink.width, logical.width);
>
>    pango_layout_get_pixel_extents (layout,&ink,&logical);
>    printf ("pixel extents: ink width=%d, logical width=%d\n",
>            ink.width, logical.width);
>
>    /* Clean up. */
>    g_object_unref (layout);
>
>    cairo_destroy (cr);
>
>    cairo_surface_finish (surface);
>    status = cairo_surface_status (surface);
>    cairo_surface_destroy (surface);
>
>    if (status != CAIRO_STATUS_SUCCESS)
>      {
>        g_printerr ("Could not save pdf to '%s'\n", filename);
>        return 1;
>      }
>
>    return 0;
> }
> --
> Ben Pfaff
> http://benpfaff.org
>
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