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diff --git a/manuals/chickadee/Grids.html b/manuals/chickadee/Grids.html new file mode 100644 index 0000000..ef364be --- /dev/null +++ b/manuals/chickadee/Grids.html @@ -0,0 +1,214 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 2017-2021 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. + + +* Chickadee: (chickadee). Game programming toolkit for Guile. + +The document was typeset with +http://www.texinfo.org/ (GNU Texinfo). + --> +<!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ --> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<title>Grids (The Chickadee Game Toolkit)</title> + +<meta name="description" content="Grids (The Chickadee Game Toolkit)"> +<meta name="keywords" content="Grids (The Chickadee Game Toolkit)"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<link href="index.html" rel="start" title="Top"> +<link href="Index.html" rel="index" title="Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Data-Structures.html" rel="up" title="Data Structures"> +<link href="Path-Finding.html" rel="next" title="Path Finding"> +<link href="Quadtrees.html" rel="prev" title="Quadtrees"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.indentedblock {margin-right: 0em} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +kbd {font-style: oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +span.nolinebreak {white-space: nowrap} +span.roman {font-family: initial; font-weight: normal} +span.sansserif {font-family: sans-serif; font-weight: normal} +ul.no-bullet {list-style: none} +@media (min-width: 1140px) { + body { + margin-left: 14rem; + margin-right: 4rem; + max-width: 52rem; + } +} + +@media (min-width: 800px) and (max-width: 1140px) { + body { + margin-left: 6rem; + margin-right: 4rem; + max-width: 52rem; + } +} + +@media (max-width: 800px) { + body { + margin: 1rem; + } +} + +--> +</style> +<link rel="stylesheet" type="text/css" href="https://dthompson.us/css/dthompson.css"> + + +</head> + +<body lang="en"> +<span id="Grids"></span><div class="header"> +<p> +Next: <a href="Path-Finding.html" accesskey="n" rel="next">Path Finding</a>, Previous: <a href="Quadtrees.html" accesskey="p" rel="prev">Quadtrees</a>, Up: <a href="Data-Structures.html" accesskey="u" rel="up">Data Structures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<span id="Grids-1"></span><h4 class="subsection">5.6.5 Grids</h4> + +<p>The <code>(chickadee data grid)</code> module provides a simple spatial +partitioning system for axis-aligned bounding boxes +(see <a href="Rectangles.html">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 “filter” 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’t waste time checking if they really do collide because it +doesn’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’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 id="index-make_002dgrid">Procedure: <strong>make-grid</strong> <em>[cell-size 64]</em></dt> +<dd><p>Return a new grid partitioned into <var>cell-size</var> tiles. +</p></dd></dl> + +<dl> +<dt id="index-grid_003f">Procedure: <strong>grid?</strong> <em>obj</em></dt> +<dd><p>Return <code>#t</code> if <var>obj</var> is a grid. +</p></dd></dl> + +<dl> +<dt id="index-cell_003f">Procedure: <strong>cell?</strong> <em>obj</em></dt> +<dd><p>Return <code>#t</code> if <var>obj</var> is a grid cell. +</p></dd></dl> + +<dl> +<dt id="index-cell_002dcount">Procedure: <strong>cell-count</strong> <em>cell</em></dt> +<dd><p>Return the number of items in <var>cell</var>. +</p></dd></dl> + +<dl> +<dt id="index-grid_002dcell_002dsize">Procedure: <strong>grid-cell-size</strong> <em>grid</em></dt> +<dd><p>Return the cell size of <var>grid</var>. +</p></dd></dl> + +<dl> +<dt id="index-grid_002dcell_002dcount">Procedure: <strong>grid-cell-count</strong> <em>grid</em></dt> +<dd><p>Return the number of cells currently in <var>grid</var>. +</p></dd></dl> + +<dl> +<dt id="index-grid_002ditem_002dcount">Procedure: <strong>grid-item-count</strong> <em>grid</em></dt> +<dd><p>Return the number of items in <var>grid</var>. +</p></dd></dl> + +<dl> +<dt id="index-grid_002dadd">Procedure: <strong>grid-add</strong> <em>grid item x y width height</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 id="index-grid_002dremove">Procedure: <strong>grid-remove</strong> <em>grid item</em></dt> +<dd><p>Return <var>item</var> from <var>grid</var>. +</p></dd></dl> + +<dl> +<dt id="index-grid_002dclear">Procedure: <strong>grid-clear</strong> <em>grid</em></dt> +<dd><p>Remove all items from <var>grid</var>. +</p></dd></dl> + +<dl> +<dt id="index-grid_002dmove">Procedure: <strong>grid-move</strong> <em>grid item position filter</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 id="index-for_002deach_002dcell">Procedure: <strong>for-each-cell</strong> <em>proc grid [rect]</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 id="index-for_002deach_002ditem">Procedure: <strong>for-each-item</strong> <em>proc grid</em></dt> +<dd><p>Call <var>proc</var> for each item in <var>grid</var>. +</p></dd></dl> + +<dl> +<dt id="index-slide">Procedure: <strong>slide</strong> <em>item item-rect other other-rect goal</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="Path-Finding.html" accesskey="n" rel="next">Path Finding</a>, Previous: <a href="Quadtrees.html" accesskey="p" rel="prev">Quadtrees</a>, Up: <a href="Data-Structures.html" accesskey="u" rel="up">Data Structures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |