code: public boolean setKerning(int char1, int char2, int kern) {
          int metrics[] = getMetricsTT(char1);
          if (metrics == null)
              return false;
          int c1 = metrics[0];
          metrics = getMetricsTT(char2);
          if (metrics == null)
              return false;
          int c2 = metrics[0];
          kerning.put((c1 << 16) + c2, kern);
          return true;
      }
docs: Sets the kerning between two Unicode chars.
  @param char1 the first char
  @param char2 the second char
  @param kern the kerning to apply in normalized 1000 units
  @return <code>true</code> if the kerning was applied, <code>false</code> otherwise