36 lines
2.3 KiB
XML
36 lines
2.3 KiB
XML
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<title>Behind the Scenes</title>
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<section id='&s2.idroot;howworks'>
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<title>How it all works, in a nutshell</title>
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<para>
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The web app get a request and decides what user it's for, and what type of resource it's for.
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</para>
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<para>The web application loads the user's style for that resource and then loads each
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layer for that style, unless it's already loaded. (layers are selectively cached) </para>
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<para>
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The S2 system builds a <emphasis role="bold">context</emphasis> which contains the property values
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set by the top-most layer for each property, as well as a function vtable
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computed the same way. </para>
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<para>
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Next the web application invokes the global <function>prop_init()</function> function which the layout layer might've
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implemented. The job of this function is to initialize the <emphasis role="bold">constructional properties</emphasis>.
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Constructional properties are properties which the web app looks at to influence
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its subsequent data structure population. For example, FotoBilder examines
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the value of <varname>$*gallery_max_page_size</varname> to determine how many thumbnails
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to load and return for a gallery. However, a layout wouldn't always want
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to directly expose this property to the users. What if the layout was a
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grid and the user wanted a page size that was a prime number? How do you
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make an even grid out of 37 pictures? This sort of layout should ask the
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user for the number of rows and columns they want, then compute <varname>$*gallery_max_page_size</varname>
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in <function>prop_init()</function> by multiplying <varname>$*rows</varname> and <varname>$*cols</varname>.
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</para>
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<para> The web app looks at the current context and determines both the version
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number of the core layer and the values of all the constructional properties,
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then builds an appropriate data-structure for the resource requested. This
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instantiated object is likely pretty deep, containing dozens of instantiated
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objects all hanging off it. </para>
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<para>
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The web app invokes the entry point method (probably called <function>->print()</function>)
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on the object it just instantiated. From here, S2 code runs, printing what
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it wants, and invoking methods on other objects in its huge data structure
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which may also print. </para>
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</section>
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