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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-&gt;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>
</related-links></concept>