+ * We want to display every character from this string in
+ * the centre of its own character cell. In the worst case,
+ * this requires a separate text-drawing call for each
+ * character; but in the common case where the font is
+ * properly fixed-width, we can draw many characters in one
+ * go which is much faster.
+ *
+ * This still isn't really ideal. If you look at what
+ * happens in the X protocol as a result of all of this, you
+ * find - naturally enough - that each call to
+ * gdk_draw_layout() generates a separate set of X RENDER
+ * operations involving creating a picture, setting a clip
+ * rectangle, doing some drawing and undoing the whole lot.
+ * In an ideal world, we should _always_ be able to turn the
+ * contents of this loop into a single RenderCompositeGlyphs
+ * operation which internally specifies inter-character
+ * deltas to get the spacing right, which would give us full
+ * speed _even_ in the worst case of a non-fixed-width font.
+ * However, Pango's architecture and documentation are so
+ * unhelpful that I have no idea how if at all to persuade
+ * them to do that.
+ */
+
+ /*
+ * Start by extracting a single UTF-8 character from the
+ * string.