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<span id="Quadtrees"></span><div class="header">
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<hr>
<span id="Quadtrees-1"></span><h4 class="subsection">5.6.4 Quadtrees</h4>
<p>The <code>(chickadee data quadtree)</code> module provides a 2D spatial
partitioning implementation known as a “quadtree”. A quadtree
recursively subdivides the world into rectangular quadrants. This
data structure is very useful for handling broad-phase collision
detection because it can quickly determine the objects that may
possibly be colliding with another, resulting in fewer narrow-phase
collision tests that are typically much more expensive.
</p>
<dl>
<dt id="index-make_002dquadtree">Procedure: <strong>make-quadtree</strong> <em>bounds [#:max-size 5] [#:max-depth 4]</em></dt>
<dd><p>Return a new quadtree that covers the area <var>bounds</var>. Each node
will try to hold at maximum <var>max-size</var> objects and the tree depth
will be restricted to <var>max-depth</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_003f">Procedure: <strong>quadtree?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a quadtree.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dclear_0021">Procedure: <strong>quadtree-clear!</strong> <em>quadtree</em></dt>
<dd><p>Clear all objects from <var>quadtree</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dinsert_0021">Procedure: <strong>quadtree-insert!</strong> <em>quadtree rect object</em></dt>
<dd><p>Insert <var>object</var> with bounding box <var>rect</var> into <var>quadtree</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002ddelete_0021">Procedure: <strong>quadtree-delete!</strong> <em>quadtree rect object</em></dt>
<dd><p>Delete <var>object</var>, who occupies the space <var>rect</var>, from
<var>quadtree</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dfind">Procedure: <strong>quadtree-find</strong> <em>rect pred</em></dt>
<dd><p>Return the first object in <var>quadtree</var> in the vicinity of
<var>rect</var> that satisfies <var>pred</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dfold">Procedure: <strong>quadtree-fold</strong> <em>quadtree rect init proc</em></dt>
<dd><p>Apply <var>proc</var> to all objects in the vicinity of <var>rect</var> in
<var>quadtree</var> to build a result and return that result. <var>init</var>
is the initial result. If there are no objects in the vicinity of
<var>rect</var>, just <var>init</var> is returned.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dfor_002deach">Procedure: <strong>quadtree-for-each</strong> <em>quadtree rect proc</em></dt>
<dd><p>Call <var>proc</var> for all objects in the vicinity of <var>rect</var> in
<var>quadtree</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dleaf_003f">Procedure: <strong>quadtree-leaf?</strong> <em>quadtree</em></dt>
<dd><p>Return <code>#t</code> if <var>quadtree</var> is a leaf node.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dbounds">Procedure: <strong>quadtree-bounds</strong> <em>quadtree</em></dt>
<dd><p>Return the bounding rectangle of <var>quadtree</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dmax_002ddepth">Procedure: <strong>quadtree-max-depth</strong> <em>quadtree</em></dt>
<dd><p>Return the maximum depth of <var>quadtree</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dmax_002dsize">Procedure: <strong>quadtree-max-size</strong> <em>quadtree</em></dt>
<dd><p>Return the desired per-node maximum object count of <var>quadtree</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002ddepth">Procedure: <strong>quadtree-depth</strong> <em>quadtree</em></dt>
<dd><p>Return the depth of the node <var>quadtree</var>.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dsize">Procedure: <strong>quadtree-size</strong> <em>quadtree</em></dt>
<dd><p>Return the number of objects stored in the node <var>quadtree</var>.
</p></dd></dl>
<p>Non-leaf nodes always have four child nodes, which correspond to the
quadrants of a Cartesian coordinate system:
</p>
<pre class="verbatim">*------*------*
| | |
| Q2 | Q1 |
| | |
*------*------*
| | |
| Q3 | Q4 |
| | |
*------*------*
</pre>
<dl>
<dt id="index-quadtree_002dq1">Procedure: <strong>quadtree-q1</strong> <em>quadtree</em></dt>
<dd><p>Return the upper-right child node of <var>quadtree</var>, or <code>#f</code> if
<var>quadtree</var> is a leaf node.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dq2">Procedure: <strong>quadtree-q2</strong> <em>quadtree</em></dt>
<dd><p>Return the upper-left child node of <var>quadtree</var>, or <code>#f</code> if
<var>quadtree</var> is a leaf node.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dq3">Procedure: <strong>quadtree-q3</strong> <em>quadtree</em></dt>
<dd><p>Return the lower-left child node of <var>quadtree</var>, or <code>#f</code> if
<var>quadtree</var> is a leaf node.
</p></dd></dl>
<dl>
<dt id="index-quadtree_002dq4">Procedure: <strong>quadtree-q4</strong> <em>quadtree</em></dt>
<dd><p>Return the lower-right child node of <var>quadtree</var>, or <code>#f</code> if
<var>quadtree</var> is a leaf node.
</p></dd></dl>
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