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<concept id="GUID-F477E82D-2929-5C69-BF6D-A69A61AC9EA5" xml:lang="en"><title>Creating

a Font Rasterizer Plug-in</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<section><title>Overview</title> <p>The steps required to write a font rasterizer

DLL are: </p> <ul>

<li id="GUID-C0A88FBF-7D70-5EAC-8754-41AE322A80E0"><p>Implement an exported <codeph>NewL()</codeph> factory

function to create rasterizer objects (which you derive from <codeph>COpenFontRasterizer</codeph>).

You may choose to implement this as part of your rasterizer object. </p> </li>

<li id="GUID-1ED7EC05-4217-5FA5-AFBC-D25C1517343F"><p>Write a class derived

from <codeph>COpenFontRasterizer</codeph>. This will need to store any context

associated with the rasterization process rather than with individual typefaces.

It also implements a function to create your <codeph>COpenFontFile</codeph> derived

objects. </p> </li>

<li id="GUID-7B5E3CCB-FD32-554F-9BBE-2784C98FEB4B"><p>Write a class derived

from <codeph>COpenFontFile</codeph>. This class manages a single file representing

a typeface. </p> </li>

<li id="GUID-EA14EC9D-615D-5344-A91C-3171A51E3208"><p>Write a class derived

from <codeph>COpenFont</codeph>. </p> </li>

<li id="GUID-8D14151F-B779-5B31-B94D-F4FFA2D8F093"><p>Place all the code into

a DLL of the right type and provide an exported function to create the rasterizer

object. </p> </li>

</ul> <p>Deriving from <codeph>COpenFontRasterizer</codeph>, <codeph>COpenFontFile</codeph> and <codeph>COpenFont</codeph> are

discussed in the "See also" topics below. This section describes the operations

required to package the code as a polymorphic DLL. </p> <p>For more information,

see: </p> <ul>

<li id="GUID-13833E45-6481-5D93-847D-06F09BFA2717"><p> <xref href="GUID-1CF78E25-8C83-5812-AE6F-8612B3F9CDA9.dita">Deriving

from COpenFontRasterizer</xref>  </p> </li>

<li id="GUID-6ED0A7A3-8DB8-556D-8B77-46DA7D448D6F"><p> <xref href="GUID-BCF6FEF0-1792-5DEA-A2D7-896E47163547.dita">Deriving

from COpenFontFile</xref>  </p> </li>

<li id="GUID-94F5442E-9A77-53BB-B42E-316C62DCB032"><p> <xref href="GUID-5A89E3C4-DEE7-5823-A109-92ED0D87B58C.dita">Deriving

from COpenFont</xref>  </p> </li>

<li id="GUID-027B74C4-6CE7-5D33-B00B-33016734189E"><p> <xref href="GUID-F44D974F-AADE-5E6C-8D69-8D3EEE4BD395.dita">Deriving

from COpenFontRasterizerContext</xref>  </p> </li>

</ul> </section>

<section><title>The DLL</title> <p>A font rasterizer DLL is an ordinary Symbian

polymorphic DLL. It exports just one function and has no unusual behavior. </p> <p>In

particular, it must have no writable static data. This is an important constraint

on the use of code from outside sources. See <xref href="GUID-5BDE6462-E6CA-5738-A587-C7D875574789.dita">Static

Data</xref> for more information. </p> </section>

<section id="GUID-ADA409CE-7326-5586-8DC4-B1E3FEBCE070"><title>The exported

function</title> <p>The exported function is a factory function that creates

objects of a class derived from <codeph>COpenFontRasterizer</codeph>. It will

be called just once — when the Font and Bitmap Server loads the DLL. </p> <p>Although

the name of the function does not matter because it is loaded by ordinal,

implementers should follow the practice of making it a static member of the

rasterizer class, called <codeph>NewL()</codeph>. Therefore, if the rasterizer

class is <codeph>CExampleRasterizer</codeph> (derived from <codeph>COpenFontRasterizer</codeph>),

the exported function is: </p> <codeblock id="GUID-45589D16-BF32-54F0-ADFB-566231281110" xml:space="preserve">static COpenFontRasterizer* CExampleRasterizer::NewL()</codeblock> <p>The function must take no arguments. It must create a <codeph>COpenFontRasterizer</codeph> derived

object on the heap, returning it to the caller. The caller is responsible

for deleting the object. As the name of the example function suggests, it

is allowed to leave. </p><p><b>Example </b> </p> <p>The exported function

used in the FreeType rasterizer is given below: </p> <codeblock id="GUID-1B22E569-A3DD-52B6-AEA2-F1CF8A721BAB" xml:space="preserve">EXPORT_C COpenFontRasterizer* CFreeTypeRasterizer::NewL()

    {

    CFreeTypeRasterizer* r = new(ELeave) CFreeTypeRasterizer;

    CleanupStack::PushL( r );

    r->iContext = CFreeTypeContext::NewL();

    CleanupStack::Pop();

    return r;

    }

</codeblock> </section>

<section><title>Project file</title> <p>The name of the rasterizer DLL, its

type, and its UIDs are all specified in the MMP file. Note that: </p> <ul>

<li id="GUID-AAD480A0-9010-5999-9677-9F7C1C94EC2F"><p>All capabilities except

TCB (Trusted Computing Base) are required. </p> </li>

<li id="GUID-38FDC5A5-5AA4-530C-AC34-D6BBE852959C"><p>The <i>targettype</i> must

be <b>PLUGIN </b>. </p> </li>

<li id="GUID-7EE45983-7578-527C-97A6-88ABFFA4EEBB"><p>The <i>UID</i> line

identifies the project's UID2 and UID3 values. UID2 must be <codeph>0x10009D8D</codeph>,

which identifies the DLL as an ECOM plug-in. UID3 must be <codeph>0x100012A7</codeph>,

which identifies the ECOM plug-in as a font rasterizer. </p> </li>

</ul> <p><b>Example </b> </p> <p>A fragment of the project file for the freetype

DLL is given below. </p> <codeblock id="GUID-1E2029EE-E2C8-5D48-B965-A8EBC991C513" xml:space="preserve">target freetype.dll

CAPABILITY All -Tcb

targettype PLUGIN

UID 0x10003B1F 0x100012A7</codeblock> </section>

<section><title>Header files</title> <p>Font rasterizer DLLs must <codeph>#include</codeph> the

following header files, which are located in the standard include directory <filepath>\epoc32\include\</filepath>: </p> <ul>

<li id="GUID-29A10FF8-E5F4-5FF3-AAE9-5DB6769672B7"><p> <filepath>openfont.h</filepath> for

the Font Store classes </p> </li>

<li id="GUID-E85D522E-5EA4-5931-906B-1C9B190BE61E"><p> <filepath>e32uid.h</filepath> for

the UID value for a dynamic library </p> </li>

<li id="GUID-BB94D8BC-24B2-5BE3-8C46-9394FE3585A6"><p> <filepath>f32file.h</filepath> for

the file handling classes </p> </li>

</ul> </section>

</conbody><related-links>

<link href="GUID-1CF78E25-8C83-5812-AE6F-8612B3F9CDA9.dita"><linktext>Deriving

from COpenFontRasterizer</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>

<link href="GUID-5BDE6462-E6CA-5738-A587-C7D875574789.dita"><linktext>Static data</linktext>

</link>