libgimpbase: add gimp_units_to_points()

because points is used in quite some external APIs (like Pango), and
having one conversion from gimp units is better than duplicating the
code.

libgimpbase/gimpbase.def

@@ -120,6 +120,7 @@ EXPORTS
 	gimp_unit_new
 	gimp_unit_set_deletion_flag
 	gimp_units_to_pixels
+	gimp_units_to_points
 	gimp_user_directory
 	gimp_user_directory_get_type
 	gimp_utf8_strtrim

libgimpbase/gimpunit.c

@@ -654,3 +654,30 @@ gimp_units_to_pixels (gdouble  value,
 
   return value * resolution / gimp_unit_get_factor (unit);
 }
+
+/**
+ * gimp_units_to_points:
+ * @value:      value in units
+ * @unit:       unit of @value
+ * @resolution: resloution in DPI
+ *
+ * Converts a @value specified in @unit to points.
+ *
+ * Returns: @value converted to points.
+ *
+ * Since: GIMP 2.8
+ **/
+gdouble
+gimp_units_to_points (gdouble  value,
+                      GimpUnit unit,
+                      gdouble  resolution)
+{
+  if (unit == GIMP_UNIT_POINT)
+    return value;
+
+  if (unit == GIMP_UNIT_PIXEL)
+    return (value * gimp_unit_get_factor (GIMP_UNIT_POINT) / resolution);
+
+  return (value *
+          gimp_unit_get_factor (GIMP_UNIT_POINT) / gimp_unit_get_factor (unit));
+}

libgimpbase/gimpunit.h

@@ -92,6 +92,9 @@ gdouble       gimp_pixels_to_units          (gdouble      pixels,
 gdouble       gimp_units_to_pixels          (gdouble      value,
                                              GimpUnit     unit,
                                              gdouble      resolution);
+gdouble       gimp_units_to_points          (gdouble      value,
+                                             GimpUnit     unit,
+                                             gdouble      resolution);
 
 
 G_END_DECLS