kc3-lang/freetype/docs/design/design-2.html
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Hash : 4cd68a09
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Date : 2000-10-25T23:42:02
updating the FT2 design documentation - note that the "modules.html" will soon disappear, it is now replaced by a more general and more detailed series of pages named "design-??.html" - the images have been seriously reworked, more will come tomorrow
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docs/design/design-2.html
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<html> <head><title>The Design of FreeType 2 - Basic Design</title> <basefont face="Georgia, Arial, Helvetica, Geneva"> <style content="text/css"> P { text-align=justify } H1 { text-align=center } H2 { text-align=center } LI { text-align=justify } </style> </head> <body text=#000000 bgcolor=#ffffff> <center><table width="500"><tr><td> <center><h1>The Design of FreeType 2</h1></center> <table width="100%" cellpadding=5><tr bgcolor="#ccccee"><td> <h1>I. Components and APIs</h1> </td></tr></table> <p>It's better to describe FreeType 2 as a collection of <em>components</em>. Each one of them is a more or less abstract part of the library that is in charge of one specific task. We will now explicit the connections and relationships between them.</p> <p>A first brief description of this system of components could be:</p> <ul> <li><p> client applications typically call the FreeType 2 <b>high-level API</b>, whose functions are implemented in a single component called the <em>Base Layer</em>. </p></li> <li><p> depending on the context or the task, the base layer then calls one or more <em>module</em> components to perform the work. In most cases, the client application doesn't need to know what module was called. </p></li> <li><p> the base layer also contains a set of routines that are used for generic things like memory allocation, list processing, i/o stream parsing, fixed point computation, etc.. these functions can also be called by a module at any time, and they form what is called the <b>low-level base API</b>. </p></li> </ul> <p>This is illustrated by the following graphics (note that component entry points are represented as colored triangles):</p> <center><img src="basic-design.png" width="394" height="313"></center> <p>Now, a few additional things must be added to complete this picture:</p> <ul> <li><p>some parts of the base layer can be replaced for specific builds of the library, and can thus be considered as components themselves. this is the case for the <b>ftsystem</b> component, which is in charge of implementing memory management & input stream access, as well as the <b>ftinit</b>, which is in charge of library initialisation (i.e. implementing <tt>FT_Init_FreeType</tt>). </p></li> <li><p> FreeType 2 comes also with a set of <em>optional components</em>, which can be used either as a convenience for client applications (e.g. the <b>ftglyph</b> component, used to provide a simple API to manage glyph images independently of their internal representation), or to access format-specific features (e.g. the <b>ftmm</b> component used to access and manage Multiple Masters data in Type 1 fonts) </p></li> <li><p> Finally, a module is capable of calling functions provided by another module. This is very useful to share code and tables between several font driver modules (for example, the <tt>truetype</tt> and <tt>cff</tt> both use the routines provided by the <tt>sfnt</tt> module). </p></li> </ul> <p>Hence, a more complete picture would be:</p> <center><img src="detailed-design.png" width="390" height="429"></center> <p>Please take note of the following important points:</p> <ul> <li><p> an optional component can use either the high-level or base API. This is the case of <b>ftglyph</b> in the above picture. </p></li> <li><p> some optional component can use module-specific interfaces ignored by the base layer. In the above example, <b>ftmm</b> directly accesses the Type 1 module to set/query data </p></li> <li><p> a replacable component can provide a function of the high-level API. For example, <b>ftinit</b> provides <tt>FT_Init_FreeType</tt> to client applications. </p></li> </ul> </td></tr></table></center> </body> </html>