pango example

From the gnome-pango manual, version 2.16.1 --

"Some example code would be really nice here; I don't have any at the
moment. So send something to the guile-gnome list and be famous on the
interwebs!"

On that note - here is a short program (attached) making use of the
(gnome pango) capabilities.

One issue came up - the pango API defines a macro PANGO_SCALE, an
integer value needed for conversion between pixels and "pango units".
As far as I can tell, (gnome pango) does not export this value or any
binding which does the conversion.  The manual mentions
"<pango-glyph-unit>" but this symbol is not bound by (gnome pango).
An easy workaround is to just hardcode the value of PANGO_SCALE into
your scheme code, on the theory that PANGO_SCALE has never changed and
probably never will - but still, it would be nice to use the actual
value from the pango library.

One solution is to wrap a newer version of the pango library.
guile-gnome-platform-2.16.1 depends on pango-1.14 or later.
Pango-1.16 and later define a function pango_units_from_double() which
takes care of the PANGO_SCALE conversion.  I tried regenerating
pango.defs from the latest pango (1.24).  I had to apply the patch
below to get it to compile.  In the resulting (gnome pango),
"pango-units-from-double" is bound and does the proper conversion.


diff --git a/gnome/overrides/pango.defs b/gnome/overrides/pango.defs
index 48c2c4c..54b24d6 100644
--- a/gnome/overrides/pango.defs
+++ b/gnome/overrides/pango.defs
@@ -174,6 +174,13 @@
  (return-type "GSList*-of-PangoLayoutLine*")
 )

+(define-method get_lines_readonly
+  (of-object "PangoLayout")
+  (c-name "pango_layout_get_lines_readonly")
+  (overrides "pango_layout_get_lines_readonly")
+  (return-type "GSList*-of-PangoLayoutLine*")
+)
+
 (ignore "pango_attr_shape_new_with_data"
        "pango_attr_iterator_get_font"
        "pango_attr_list_filter"

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