92 lines
3.0 KiB
HTML
92 lines
3.0 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>Data Structures</title>
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<link href="style.css" rel="stylesheet" type="text/css">
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</head>
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<body background="images/back.gif">
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<!--START-->
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<h1>Data structures</h1>
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<i><b>This functionality is only available in the Pro Edition of Game Maker.</b></i>
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<p>
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In games you often need to store information. For example you need to store
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lists of items that a person carries or you want to store places that still
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need to be visited. You can use the arrays for this. But if you want to do more
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complicated operations, like sorting the data or searching for a particular item,
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you need to write large pieces of GML code which can be slow to execute.
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<p>
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To remedy this, <i>Game Maker</i> has a number of built-in data
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structures that can be accessed through functions. At the moment
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there are six different types of data structure available: stacks,
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queues, lists, maps, priority queues, and grids. Each of these data structures
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is tuned for a particular type of use (see below).
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<p>
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All data structures work globally in the same way. You can create a data
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structure with a function that returns an id for the structures. You use
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this id to perform operations on the data structures. Once you are done
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you destroy the data structure again to save storage. You can use as many
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of the structures at the same moment as you want. All structure can store
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both strings and real values.
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<p>
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Please note that data structures and their content are not saved when you
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save the game using the actions or functions for that. If you use data
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structures and want to allow for saves you have to create your own mechanism
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for that.
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<p>
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When comparing values, for example when searching in a map or sorting a list,
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<i>Game Maker</i> must decide when two values are equal. For strings and integer
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values this is clear but for real numbers, due to round-off errors, equal number
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can easily become unequal. For example (5/3)*3 will not be equal to 5. To avoid
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this, a precision is used. When the difference between two numbers is smaller
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than this precision they are considered equal. Default a precision of 0.0000001
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is used. You can change this precision using the following function:
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<p>
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<blockquote>
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<tt><b>ds_set_precision(prec)</b></tt>
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Sets the precision used for comparisons.<br>
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</blockquote>
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<p>
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This precision is used in all data structures but not in other comparisons in GML!
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<!--HELPONLY-->
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<P>
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Information on data structures can be found in the following pages:
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<P>
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<p>
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<blockquote>
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<a href="411_01_stacks.html">Stacks</a><br>
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<a href="411_02_queues.html">Queues</a><br>
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<a href="411_03_lists.html">Lists</a><br>
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<a href="411_04_maps.html">Maps</a><br>
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<a href="411_05_priority.html">Priority Queues</a><br>
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<a href="411_06_grid.html">Grids</a><br>
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</blockquote>
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<p>
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<!--ENDHELPONLY-->
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<!--END-->
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</body>
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</html>
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<!-- KEYWORDS
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data structures
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ds_set_precision()
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-->
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