Update Chickadee manual and home page for 0.3.0.

Better late than never!
author: David Thompson <dthompson2@worcester.edu> 2018-12-12 09:20:10 -0500
committer: David Thompson <dthompson2@worcester.edu> 2018-12-12 09:20:10 -0500
commit: f16fed3d50fd3d56deb46a3d4641a81460e389de (patch)
tree: 71659ed643b65eadb17110b3f8f0c5d5cfdd3031 /manuals/chickadee/Grid.html
parent: c4b418c2dcfba3c741f67058a51a3e490aa4b297 (diff)
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+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<!-- Copyright (C) 2017  David Thompson davet@gnu.org
+
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.3
+or any later version published by the Free Software Foundation;
+with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
+A copy of the license is included in the section entitled "GNU
+Free Documentation License".
+
+A copy of the license is also available from the Free Software
+Foundation Web site at http://www.gnu.org/licenses/fdl.html.
+
+
+The document was typeset with
+http://www.texinfo.org/ (GNU Texinfo).
+ -->
+<!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+<title>Grid (The Chickadee Game Toolkit)</title>
+
+<meta name="description" content="Grid (The Chickadee Game Toolkit)">
+<meta name="keywords" content="Grid (The Chickadee Game Toolkit)">
+<meta name="resource-type" content="document">
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+<link href="index.html#Top" rel="start" title="Top">
+<link href="Index.html#Index" rel="index" title="Index">
+<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
+<link href="Math.html#Math" rel="up" title="Math">
+<link href="Matrices.html#Matrices" rel="next" title="Matrices">
+<link href="Rectangles.html#Rectangles" rel="prev" title="Rectangles">
+<style type="text/css">
+<!--
+a.summary-letter {text-decoration: none}
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+        margin-right: 4rem;
+        max-width: 52rem;
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+    body {
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+<link rel="stylesheet" type="text/css" href="https://dthompson.us/css/dthompson.css">
+
+
+</head>
+
+<body lang="en">
+<a name="Grid"></a>
+<div class="header">
+<p>
+Next: <a href="Matrices.html#Matrices" accesskey="n" rel="next">Matrices</a>, Previous: <a href="Rectangles.html#Rectangles" accesskey="p" rel="prev">Rectangles</a>, Up: <a href="Math.html#Math" accesskey="u" rel="up">Math</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html#Index" title="Index" rel="index">Index</a>]</p>
+</div>
+<hr>
+<a name="Grid-1"></a>
+<h4 class="subsection">2.2.4 Grid</h4>
+
+<p>The <code>(chickadee math grid)</code> module provides a simple spatial
+partitioning system for axis-aligned bounding boxes
+(see <a href="Rectangles.html#Rectangles">Rectangles</a>) in 2D space.  The grid divides the world into
+tiles and keeps track of which rectangles occupy which tiles.  When
+there are lots of moving objects in the game world that need collision
+detection, the grid greatly speeds up the process.  Instead of
+checking collisions of each object against every other object (an
+O(n^2) operation), the grid quickly narrows down which objects could
+possibly be colliding and only performs collision testing against a
+small set of objects.
+</p>
+<p>In addition to checking for collisions, the grid also handles the
+resolution of collisions.  Exactly how each collision is resolved is
+user-defined.  A player bumping into a wall may slide against it.  An
+enemy colliding with a projectile shot by the player may get pushed
+back in the opposite direction.  Two players colliding may not need
+resolution at all and will just pass through each other.  The way this
+works is that each time an object (A) is moved within the grid, the
+grid looks for an object (B) that may possibly be colliding with A.  A
+user-defined procedure known as a &ldquo;filter&rdquo; is then called with both
+A and B.  If the filter returns <code>#f</code>, it means that even if A and
+B are colliding, no collision resolution is needed.  In this case the
+grid won&rsquo;t waste time checking if they really do collide because it
+doesn&rsquo;t matter.  If A and B are collidable, then the filter returns a
+procedure that implements the resolution technique.  The grid will
+then perform a collision test.  If A and B are colliding, the resolver
+procedure is called.  It&rsquo;s the resolvers job to adjust the objects
+such that they are no longer colliding.  The grid module comes with a
+very simple resolution procedure, <code>slide</code>, that adjusts object A
+by the smallest amount so that it no longer overlaps with B.  By using
+this filtering technique, a game can resolve collisions between
+different objects in different ways.
+</p>
+<dl>
+<dt><a name="index-make_002dgrid"></a>Procedure: <strong>make-grid</strong> <em>[<var>cell-size</var> 64]</em></dt>
+<dd><p>Return a new grid partitioned into <var>cell-size</var> tiles.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-grid_003f"></a>Procedure: <strong>grid?</strong> <em><var>obj</var></em></dt>
+<dd><p>Return <code>#t</code> if <var>obj</var> is a grid.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-cell_003f"></a>Procedure: <strong>cell?</strong> <em><var>obj</var></em></dt>
+<dd><p>Return <code>#t</code> if <var>obj</var> is a grid cell.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-cell_002dcount"></a>Procedure: <strong>cell-count</strong> <em><var>cell</var></em></dt>
+<dd><p>Return the number of items in <var>cell</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-grid_002dcell_002dsize"></a>Procedure: <strong>grid-cell-size</strong> <em><var>grid</var></em></dt>
+<dd><p>Return the cell size of <var>grid</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-grid_002dcell_002dcount"></a>Procedure: <strong>grid-cell-count</strong> <em><var>grid</var></em></dt>
+<dd><p>Return the number of cells currently in <var>grid</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-grid_002ditem_002dcount"></a>Procedure: <strong>grid-item-count</strong> <em><var>grid</var></em></dt>
+<dd><p>Return the number of items in <var>grid</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-grid_002dadd"></a>Procedure: <strong>grid-add</strong> <em><var>grid</var> <var>item</var> <var>x</var> <var>y</var>                             <var>width</var> <var>height</var></em></dt>
+<dd>
+<p>Add <var>item</var> to <var>grid</var> represented by the axis-aligned bounding
+box whose lower-left corner is at (<var>x</var>, <var>y</var>) and is
+<var>width</var> x <var>height</var> in size.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-grid_002dremove"></a>Procedure: <strong>grid-remove</strong> <em><var>grid</var> <var>item</var></em></dt>
+<dd><p>Return <var>item</var> from <var>grid</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-grid_002dclear"></a>Procedure: <strong>grid-clear</strong> <em><var>grid</var></em></dt>
+<dd><p>Remove all items from <var>grid</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-grid_002dmove"></a>Procedure: <strong>grid-move</strong> <em><var>grid</var> <var>item</var> <var>position</var> <var>filter</var></em></dt>
+<dd><p>Attempt to move <var>item</var> in <var>grid</var> to <var>position</var> (a 2D
+vector) and check for collisions.  For each collision, <var>filter</var>
+will be called with two arguments: <var>item</var> and the item it collided
+with.  If a collision occurs, <var>position</var> may be modified to
+resolve the colliding objects.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-for_002deach_002dcell"></a>Procedure: <strong>for-each-cell</strong> <em><var>proc</var> <var>grid</var> [<var>rect</var>]</em></dt>
+<dd><p>Call <var>proc</var> with each cell in <var>grid</var> that intersects
+<var>rect</var>, or every cell if <var>rect</var> is <code>#f</code>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-for_002deach_002ditem"></a>Procedure: <strong>for-each-item</strong> <em><var>proc</var> <var>grid</var></em></dt>
+<dd><p>Call <var>proc</var> for each item in <var>grid</var>.
+</p></dd></dl>
+
+<dl>
+<dt><a name="index-slide"></a>Procedure: <strong>slide</strong> <em><var>item</var> <var>item-rect</var>                          <var>other</var> <var>other-rect</var> <var>goal</var></em></dt>
+<dd>
+<p>Resolve the collision that occurs between <var>item</var> and <var>other</var>
+when moving <var>item-rect</var> to <var>goal</var> by sliding <var>item-rect</var>
+the minimum amount needed to make it no longer overlap
+<var>other-rect</var>.
+</p></dd></dl>
+
+<hr>
+<div class="header">
+<p>
+Next: <a href="Matrices.html#Matrices" accesskey="n" rel="next">Matrices</a>, Previous: <a href="Rectangles.html#Rectangles" accesskey="p" rel="prev">Rectangles</a>, Up: <a href="Math.html#Math" accesskey="u" rel="up">Math</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html#Index" title="Index" rel="index">Index</a>]</p>
+</div>
+
+
+
+</body>
+</html>
author	David Thompson <dthompson2@worcester.edu>	2018-12-12 09:20:10 -0500
committer	David Thompson <dthompson2@worcester.edu>	2018-12-12 09:20:10 -0500
commit	f16fed3d50fd3d56deb46a3d4641a81460e389de (patch)
tree	71659ed643b65eadb17110b3f8f0c5d5cfdd3031 /manuals/chickadee/Grid.html
parent	c4b418c2dcfba3c741f67058a51a3e490aa4b297 (diff)