Pango layout word wrap example

pango_layout_word_wrap.c

/*!
 * \file pango_layout_word_wrap.c
 * \brief pango layout word wrap
 *
 * \author Ben Pfaff http://benpfaff.org
 *
 * 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:
 *
<pre>
        pango_layout_set_width (layout, 1);
        pango_layout_set_wrap (layout, PANGO_WRAP_WORD);
        pango_layout_get_size (layout, &width, NULL);
</pre>
 * Later on, the width of the table column might have been adjusted upward or downward
 * or 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:
 * 
<pre>
        # ./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  |
        +------+
</pre>
 * Then giving the exact width reported by this run, plus word-char,
 * yields:
 *
<pre>
        # ./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 |
        +-----+
</pre>
 * To get word-char to produce the results that I expect, I have to add 5208,
 * which is the reported width of " ":
 *
<pre>
        # ./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  |
        +------+
</pre>
 * 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;
    PangoRectangle 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;
}


/* EOF */