PangoGlyphItem and the corresponding
text, determine the screen width corresponding to each character. When
multiple characters compose a single cluster, the width of the entire
cluster is divided equally among the characters.pangoGlyphItemGetLogicalWidths(glyph.item, text)glyph.itemtextglyph.item corresponds to
  (glyph_item->item->offset is an offset from the
   start of text)logical.widthspangoGlyphStringGetLogicalWidths.  
  Since 1.26