<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

<!-- This component and the accompanying materials are made available under the terms of the License 

"Eclipse Public License v1.0" which accompanies this distribution, 

and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

<!-- Initial Contributors:

    Nokia Corporation - initial contribution.

Contributors: 

-->

<!DOCTYPE concept

  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-90644B52-69D7-595C-95E3-D6F7A30C060D" xml:lang="en"><title>Font

and Text Services Collection Overview</title><shortdesc>A font is a set of characters of matching size (height) and appearance.

In order to be displayed each character must ultimately be drawn as a series

of pixels (a bitmap). Symbian can store fonts in bitmap or vector form. A

vector font (for example, an OpenType font) must be converted to bitmaps (or

rasterized) before it can be drawn. Symbian caches and shares bitmaps for

performance and memory efficiency. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<ul>

<li id="GUID-DB17AE5F-54E9-5288-89DB-7A38473D9C94"><p> <b>Application developers</b> can

use Font and Text Services for selecting fonts for displaying text according

to various criteria (size and typeface). </p> </li>

<li id="GUID-ECFA8635-D278-5A1F-A8E8-8BADB73FE092"><p> <b> Device creators</b> can

add fonts and font rasterizers. Fonts can be included in the ROM or installed

on user drives. </p> </li>

</ul>

<section id="GUID-9F33DD34-F5E5-5EA0-8559-7A933D230129"><title>Concepts and

terms</title> <dl>

<dlentry>

<dt>Points, twips and pixels</dt>

<dd><p>Points (1/72th inch) and twips (a twentieth of a point) are absolute

measurements of distance and specify device-independent size. Pixel sizes

are only relevant for a specific graphics device. Each graphics device (screen

or printer) must provide a mechanism for converting between pixels and twips. </p> </dd>

</dlentry>

<dlentry>

<dt>Font</dt>

<dd><p>A named set of characters of matching size (height) and <b>font style</b> (normal,

bold, italic, underline). <b>Times Roman 14 point bold</b> is an example of

a font. </p> </dd>

</dlentry>

<dlentry>

<dt>Typeface</dt>

<dd><p>A group of fonts with similar appearance. The typeface does not include

the size or font style. <b>Times</b> is an example of a typeface. Typefaces

are sometimes referred to as <b>font families</b>. </p> <p>Typefaces are grouped

generically as mono-spaced, variable width, serif, sans-serif and symbol.

This allows the grouping of typefaces that have similar characteristics, so

that an alternative font can be selected when an exact match is not found.

This means that applications can display text relatively accurately when a

specific font is not available. </p> </dd>

</dlentry>

<dlentry>

<dt>OpenType font </dt>

<dd><p>A font that is stored as vector data, which can be rasterized to any

pixel size. OpenType fonts are sometimes simply called <b>open fonts</b>.

An open font can only be used with a corresponding font rasterizer. The <xref href="GUID-A03FB1BF-F67B-519D-A904-74CA3F8375D9.dita">Font and Bitmap Server</xref> caches

rasterized fonts into bitmap form. </p> <p>OpenType is an open source vector

font format, which is similar to TrueType. Like TrueType fonts, OpenType fonts

can contain font hinting information. However the font rasterizer's use of

the font hinting information in OpenType fonts is restricted by a software

patent. </p> </dd>

</dlentry>

<dlentry>

<dt>Character</dt>

<dd><p>A single element (such as a letter, number, ligature, symbol or punctuation

mark) of written language. Each character has a unique number (its <xref href="http://www.unicode.org/standard/WhatIsUnicode.html" scope="external">Unicode</xref> code point). </p> </dd>

</dlentry>

<dlentry>

<dt>Glyph</dt>

<dd><p>A graphical representation of a character in a specific font. The mapping

between a character and a glyph is not always direct. For example, a character

may be represented by different glyphs, depending on the context. </p> </dd>

</dlentry>

<dlentry>

<dt>Font metrics</dt>

<dd><p>Measurements (such as maximum height) that are common to all of the

characters in a font. </p> </dd>

</dlentry>

<dlentry>

<dt>Character metrics</dt>

<dd><p>Measurements (such as character width) that apply to an individual

character within a font. </p> </dd>

</dlentry>

<dlentry>

<dt>Bitmap font</dt>

<dd><p>A font stored as bitmap glyphs. The size of a font is described in

pixels. However, the actual size is dependent on the pixel size of the graphics

device. </p> </dd>

</dlentry>

<dlentry>

<dt>Rasterizing</dt>

<dd><p>The process of converting drawing instructions into bitmap data. Fonts

provided in vector form (OpenType fonts) must be rasterized into fixed size

fonts before they can be used. </p> </dd>

</dlentry>

<dlentry>

<dt>Linked font</dt>

<dd><p>A virtual font or typeface created from characters from other fonts.

The component fonts must be open fonts or other linked fonts. Linked fonts

are typically used where a preferred font does not contain all of the characters

in the character set. One of the typefaces in a linked font must be designated

as the principal typeface from which any unspecified default metrics or characters

are used. </p> </dd>

</dlentry>

<dlentry>

<dt>Contextual shaping</dt>

<dd><p>In some scripts some characters are drawn differently depending on

the adjacent characters. This means that different glyphs are used to represent

a particular character in different contexts. Contextual shaping is the selection

of the appropriate glyph from several glyphs that represent a particular character

depending on the context. </p> <p>In Latin scripts, contextual shaping is

normally used only when simulating handwriting. For example, the glyph used

for the letter <b>p</b> might depend on whether the letter is at the start,

middle or end of a word, as shown in the following diagram. For example, when

it is in the middle of the word, it might have a "tail" on both sides to join

it to the letters that appear before and after. </p> <fig id="GUID-30A9DA99-E1C5-5EE5-AEB3-0BCD6DB0A692">

<title>                   Figure 1: Handwriting simulation might use different

glyphs for                   the letter p depending on its position in a word

                 </title>

<image href="GUID-8F19C257-9A41-5D38-BC8A-285D0EB16E1B_d0e640736_href.png" placement="inline"/>

</fig> <p>Contextual shaping is an essential feature of some scripts, including

Arabic and many Indian and East Asian scripts, such as Devanagari, Kannada,

Telugu, Tamil, Bengali, Malayalam and Gurmukhi. For this reason, support for

contextual shaping is sometimes referred to as <b>Brahmic support</b>. </p> </dd>

</dlentry>

<dlentry>

<dt>Text shaper</dt>

<dd><p>A plug-in that performs the contextual shaping for scripts that require

this feature. Text shapers are font and language specific. </p> </dd>

</dlentry>

<dlentry>

<dt>System font</dt>

<dd><p>A default font that is used when no font is specified. </p> </dd>

</dlentry>

</dl> </section>

<section><title>Architectural relationships</title> <p>The Font and Text Services

components are closely integrated with the Font and Bitmap Server, GDI, BitGDI

and Window Server components in the <xref href="GUID-975CBC70-81E6-5FA2-80CE-88DD2ABE9595.dita">Graphics

package</xref>. Font size is only meaningful in the context of the current

graphics device and its pixel size. Open fonts must be rasterized in the context

of the current graphics device. The diagram below shows how BitGDI implements

Graphics Devices and Contexts. </p> <fig id="GUID-36165480-E5BC-50F3-B205-5668EA7F0306">

<title>              Figure 2: The Graphics Device and Context Architecture.

           </title>

<desc><p>Note that the names of the BitGDI classes begin with <codeph>CFbs</codeph>. </p> </desc>

<image href="GUID-9D6D07D3-A93C-5290-AC08-15750AD34802_d0e640794_href.png" placement="inline"/>

</fig> <p>Applications access font services through the <xref href="GUID-71DADA82-3ABC-52D2-8360-33FAEB2E5DE9.dita">Font

and Bitmap Server (FBSERV)</xref> which caches font bitmaps in a shared heap.

The Font and Bitmap Server ensures that there is only ever a single instance

of a particular glyph bitmap in memory. However, eXecute In Place (XIP) ROM-based

bitmaps (including fonts) are used in place and are not copied into the heap. </p> <p>Use

of the Font and Bitmap Server is transparent to clients of the Window Server.

The Window Server client session (<xref href="GUID-643DDA78-C7A7-386D-AB3F-8710141DDDA9.dita"><apiname>RWsSession</apiname></xref>) automatically

creates an <xref href="GUID-E5B29AC0-4953-385F-84C5-13EE6CB77D46.dita"><apiname>RFbsSession</apiname></xref> and stores it in thread local storage

(TLS). The Font and Bitmap Server provides two client-side classes for fonts: <xref href="GUID-DE966D8B-6E00-39B6-B136-6CF29EA384D3.dita"><apiname>CFbsFont</apiname></xref> and <xref href="GUID-5E287BF6-08C1-36A2-9085-F6B61CC52550.dita"><apiname>CFbsTypefaceStore</apiname></xref>. These find and use the session in TLS automatically. Clients of the Window

Server are therefore automatically clients of the Font and Bitmap Server and

need perform no explicit session management. </p> <p>Classes representing

fonts, such as <xref href="GUID-DE966D8B-6E00-39B6-B136-6CF29EA384D3.dita"><apiname>CFbsFont</apiname></xref> (on the client side) and <xref href="GUID-25D4B920-6158-3014-8E7D-4E1C5267C5EF.dita"><apiname>CBitmapFont</apiname></xref> (on

the server side), are derived from the abstract class <xref href="GUID-2A12FE3B-47F2-3016-8161-A971CA506491.dita"><apiname>CFont</apiname></xref>. </p> <p>The <xref href="GUID-B798C19D-4030-564A-A208-D84738259D72.dita">Font Store</xref> lives in

the <xref href="GUID-71DADA82-3ABC-52D2-8360-33FAEB2E5DE9.dita">Font and Bitmap

Server</xref> and contains all of the fonts on the device and the font rasterizers

required to render them. The Font Store loads font files when the phone starts

up. It scans all of the drives on the device so that new fonts can be installed

from user drives. Font files can be loaded by the Font Store while the phone

is running. However, font rasterizers can only be installed by restarting

the phone. If a new font requires a font rasterizer to be installed, the phone

must be restarted before the font can be used. </p> <p>Open font rasterizers

are implemented as ECOM plug-ins. An open font file (represented by <xref href="GUID-FC62EDD7-A3F7-3611-A899-CA5F17BB2EEE.dita"><apiname>COpenFontFile</apiname></xref>)

can contain one or more open fonts in proprietary vector format. A corresponding

font rasterizer plug-in (<xref href="GUID-CA16238D-478A-302A-9671-97B62B0E738A.dita"><apiname>COpenFontRasterizer</apiname></xref>) must convert

the vector data into bitmaps that the Font and Bitmap Server can cache and

access using the <xref href="GUID-25D4B920-6158-3014-8E7D-4E1C5267C5EF.dita"><apiname>CBitmapFont</apiname></xref> and <xref href="GUID-039375D3-AFD9-3E31-9C1C-ACEDC10E27CE.dita"><apiname>COpenFont</apiname></xref> APIs.

Applications use rasterized open fonts by using <xref href="GUID-DE966D8B-6E00-39B6-B136-6CF29EA384D3.dita"><apiname>CFbsFont</apiname></xref> in

exactly the same way as native bitmap fonts. The open font framework means

that Symbian can support any font in any format. There is a performance impact

associated with open fonts, however, as they must be rasterized. </p> <p>Text

shapers (<xref href="GUID-FF3DFCCC-DCFE-3DD9-B497-B96C46B4FDD1.dita"><apiname>CShaper</apiname></xref>) are used for contextual scripts, which

require their glyphs to be modified according to the adjacent characters.

Text shapers are font and language specific. </p> </section>

<section><title>Components</title> <p>The Font and Text Services collection

is made up of the following components: </p> <ul>

<li id="GUID-0C4363B1-4340-5638-8A59-ECDF2AFFA088"><p><xref href="GUID-B798C19D-4030-564A-A208-D84738259D72.dita">Font

Store</xref>. This manages font matching, ownership and rasterizing. </p> </li>

<li id="GUID-AAE1BCA4-B9B4-5AD1-AC79-3308F231FCE7"><p> <xref href="GUID-75C5A614-CEC1-5832-ACEA-E3C31B8A0DE8.dita">FreeType

Font Rasterizer</xref>. This open source plug-in rasterizes OpenType fonts.

More information can be found at <xref href="http://www.freetype.org/" scope="external">www.freetype.org</xref>.

This rasterizer is normally loaded by default. </p> </li>

<li id="GUID-7EB97752-0F44-5625-8474-FDCF64654AE6"><p><xref href="GUID-DB453F9B-55B6-50C7-984D-7154F1E84AE6.dita">ICU

Layout Engine Component</xref>. A plug-in that performs contextual shaping

for specific scripts that require this feature. When a function, such as <xref href="GUID-4A501086-7EFF-376D-8901-6D9B2EB4EFF2.dita#GUID-4A501086-7EFF-376D-8901-6D9B2EB4EFF2/GUID-176B0A61-867E-35A6-AE53-0BABA48741D9"><apiname>CFbsBitGc::DrawText()</apiname></xref> draws

text in one of these scripts, internally a text shaper is used to convert

the string of characters into the appropriate series of glyphs. </p> </li>

<li id="GUID-DED869DB-C45B-51A6-B594-BA1321BC272B"><p><xref href="GUID-F4C53728-B54B-5680-82FC-9A365B45F4B5.dita">Reference

Fonts</xref>. This provides a collection of reference font files including

bitmap and OpenType fonts. By default the Symbian platform supports the DejaVu

OpenType typeface (which includes variable-width, monospaced, serif and sans

serif fonts) and legacy Calculator and Agenda symbols (which are bitmap fonts). </p> </li>

</ul> <p> <i>Note</i>: The <xref href="GUID-771AC6EC-348D-5535-9D91-5A0232BB9576.dita"> iType

Font Rasterizer</xref> is an OpenType font rasterizer from MonoType Imaging®.

This provides additional features compared to the FreeType font rasterizer,

such as four color blending, which is required for outline and shadow fonts.

This component is not provided by the Symbian Foundation because it belongs

to Monotype. However, the Symbian platform has test cases for the four color

blending that the iType Font Rasterizer provides. These test cases can be

used by device creators who obtain this font rasterizer from MonoType. </p> </section>

</conbody><related-links>

<link href="GUID-71DADA82-3ABC-52D2-8360-33FAEB2E5DE9.dita"><linktext>Font and

Bitmap Server Component Overview </linktext></link>

<link href="GUID-416A3756-B5D5-5BCD-830E-2371C5F6B502.dita"><linktext> Font Store

Component Overview</linktext></link>

</related-links></concept>