bf file format

Former-commit-id: 8d3cdbc62cc55d1361b6bb9abc8dbdbccc942af3

file-formats/bf.html

@@ -10,17 +10,18 @@
     <h1>.bf - bone forests</h1>
     <hr>
     <p>
-A .bf file contains a bone forest. That is possibly multiple bone trees, or
-skeletons. Singleton trees will be interpreted as point handles. Otherwise
-each edge in a tree will be interpreted as a bone segment.
-    </p>
+A .bf file contains a "bone forest". Normally a skeleton for linear blend
+skinning is a "bone tree" with a single root. But this format may store
+multiple trees, hence a forest.
     <p>
-Each line contains data about a vertex (joint) of a bone tree:
+Each line contains data about a vertex (joint) of the bone forest:
     </p>
     <pre><code>[weight index] [parent index] [x] [y] [z] [undocument optional data]</code></pre>
     <p>
 Indices begin with 0.  The weight index is -1 if the bone does not have an
-associated weight. The parent index is -1 for root nodes.
+associated weight. The parent index is -1 for root nodes. The x,y,z coordinates
+are offset vectors from this joint's parent's location (for roots, an offset
+from the origin).
     </p>
     <p>See also: <a href=.>file formats</a></p>
   </div>