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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="reordering-in-levels-0-and-1"></a>Reordering in levels 0 and 1</h2></div></div></div> |
| <p> |
| Another common operation in the more complex shapers is glyph |
| reordering. In order to maintain a monotonic cluster sequence |
| when glyph reordering takes place, HarfBuzz merges the clusters |
| of everything in the reordering sequence. |
| </p> |
| <p> |
| For example, let us again start with the character sequence (top |
| row) and initial cluster values (bottom row): |
| </p> |
| <pre class="programlisting"> |
| A,B,C,D,E |
| 0,1,2,3,4 |
| </pre> |
| <p> |
| If <code class="literal">D</code> is reordered to the position immediately |
| before <code class="literal">B</code>, then HarfBuzz merges the |
| <code class="literal">B</code>, <code class="literal">C</code>, and |
| <code class="literal">D</code> clusters — all the clusters between |
| the final position of the reordered glyph and its original |
| position. This means that we get: |
| </p> |
| <pre class="programlisting"> |
| A,D,B,C,E |
| 0,1,1,1,4 |
| </pre> |
| <p> |
| as the final cluster sequence. |
| </p> |
| <p> |
| Merging this many clusters is not ideal, but it is the only |
| sensible way for HarfBuzz to maintain the guarantee that the |
| sequence of cluster values remains monotonic and to retain the |
| true relationship between glyphs and characters. |
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