<?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-1CF78E25-8C83-5812-AE6F-8612B3F9CDA9" xml:lang="en"><title>Deriving
from COpenFontRasterizer</title><prolog><metadata><keywords/></metadata></prolog><conbody>
<section><title>Overview</title> <p>Classes derived from <codeph>COpenFontRasterizer</codeph> are
used to recognize font files and create objects to manage them. To derive
from <codeph>COpenFontRasterizer</codeph> you need only provide an implementation
of its pure virtual function <codeph>NewFontFileL()</codeph>. The implementation
of this function is discussed in the following section. </p> <p>The derived
class <i>should</i> also define the DLL's single exported function. This function
is discussed further in the previous topic: <xref href="GUID-F477E82D-2929-5C69-BF6D-A69A61AC9EA5.dita#GUID-F477E82D-2929-5C69-BF6D-A69A61AC9EA5/GUID-ADA409CE-7326-5586-8DC4-B1E3FEBCE070">The
exported function</xref>. </p> <p>In addition, font rasterizer classes often
need to store an 'engine context'. For example, FreeType relies on a <codeph>TT_Engine</codeph> object;
this is kept in the <codeph>CFreeTypeRasterizer</codeph>, in a <codeph>CFreeTypeRasterizerContext</codeph>.
The context is derived from <codeph>COpenFontRasterizerContext</codeph>, a
utility base class that provides functions that make it easier to write the
glyph bitmap during rasterization. </p> </section>
<section><title>Implementing NewFontFileL()</title> <p>The implementation
must examine a specified file and, if it is of the correct type, attempt to
create a <codeph>COpenFontFile</codeph> derived object to open it. The function
must return NULL if it cannot recognize the file. It may also leave if there
is an error. The caller is responsible for deleting the <codeph>COpenFontFile</codeph> object. </p> <p>The
function prototype is given below: </p> <codeblock id="GUID-25C6CABB-E2C6-52E6-BEB8-36AD98AAAD0D" xml:space="preserve">virtual COpenFontFile* NewFontFileL(TInt aUid,
        const TDesC&amp; aFileName, RFs&amp; aFileSession) = 0;</codeblock> <p> <codeph>aUid</codeph> is
an ID to be used for the font file — the application framework requires that
each typeface have a UID, so one is dynamically allocated for font files that
are not Symbian-native. The ID must be passed to the <codeph>COpenFontFile</codeph> derived
class's constructor. </p> <p> <codeph>aFileName</codeph> is the full path
and filename of the file that the font rasterizer is attempting to open. This
filename must also be passed to the <codeph>COpenFontFile</codeph> derived
class's constructor. </p> <p> <codeph>aFileSession</codeph> is the file session
owned by the Font and Bitmap server. This reference should be used for any
file access. If <codeph>COpenFontFile</codeph> derived objects need to keep
files open, <codeph>aFileSession</codeph> should be stored in a place that
is accessible to them. </p> </section>
<example><p>The FreeType implementation of <codeph>NewFontFileL()</codeph> is
given below. It recognizes the file only by its extension, relying on the
construction of the font file object to perform stricter checking.</p><codeblock id="GUID-7AA7FB45-1399-5A22-892D-2B365F8F0C60" xml:space="preserve">COpenFontFile* CFreeTypeRasterizer::NewFontFileL(TInt aUid,
    const TDesC&amp; aFileName,RFs&amp; aFileSession)
    {
    TBool is_ttf = EFalse;

    //Tests if the filename extension is ".ttf" or ".ttc".
    if (aFileName.Length() &gt; 4)
        {
        _LIT(KExtensionTTF,".ttf"); // Extension for truetype font file.
        _LIT(KExtensionTTC,".ttc"); // Extension for truetype collection file.
        TPtrC ext = aFileName.Right(4);
        if ((ext.CompareF(KExtensionTTF) == 0) | (ext.CompareF(KExtensionTTC)==0))
          is_ttf = ETrue;
        }
    // If the extension is not .ttf or .ttc then we can't read the file.
    if (!is_ttf)  
      return NULL; 
    
    //If extension is .ttf then attempt to create the font file reader.
    //return it to the caller.
    return CFreeTypeFontFile::NewL(iContext,aUid,
    aFileName,aFileSession);
    }
</codeblock></example>
</conbody><related-links>
<link href="GUID-F477E82D-2929-5C69-BF6D-A69A61AC9EA5.dita"><linktext>Creating
a Font Rasterizer Plug-in</linktext></link>
<link href="GUID-BCF6FEF0-1792-5DEA-A2D7-896E47163547.dita"><linktext>Deriving
from COpenFontFile</linktext></link>
<link href="GUID-5A89E3C4-DEE7-5823-A109-92ED0D87B58C.dita"><linktext>Deriving
from COpenFont</linktext></link>
<link href="GUID-F44D974F-AADE-5E6C-8D69-8D3EEE4BD395.dita"><linktext>Deriving
from COpenFontRasterizerContext</linktext></link>
</related-links></concept>