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<concept id="GUID-D76C7759-739D-5C98-B718-7297687FE630" xml:lang="en"><title>Extended

Bitmaps</title><shortdesc>The Font and Bitmap Server provides a framework for device creators

to add support for their own types of bitmap compression. Bitmaps that use

compression formats that are provided by device creators are known as extended

bitmaps. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p> <b>Variant</b>: <xref href="GUID-D93978BE-11A3-5CE3-B110-1DEAA5AD566C.dita">ScreenPlay</xref> and <xref href="GUID-F64E6551-670E-5E12-8103-DE504D3EC94F.dita">non-ScreenPlay</xref>. <b>Target

audience</b>: Device creators. </p>

<section><title>Natively supported bitmap formats</title> <p>Traditionally

Symbian has provided native support for bitmaps in relatively simple formats,

including the standard uncompressed bitmap format and bitmaps compressed using

simple Run-Length Encoding (RLE). The uncompressed format stores scan lines

as a sequence of individual colors, one for each pixel. The RLE compression

instead breaks each scan line into runs of consecutive pixels of the same

color. For each run it stores the color and the number of times it is repeated.

The exact details of the compression formats are internal to Symbian. </p> <p>The

natively-supported compression types are enumerated in <xref href="GUID-6E40B867-F7C6-35EA-8C6F-F54AB11BDD6E.dita"><apiname>TBitmapfileCompression</apiname></xref>.

You can use the Bitmap Conversion Tool to generate compressed bitmaps. In

addition, you can compress bitmaps at runtime by calling <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita#GUID-683A1D42-2764-3EB7-BD19-9E12559199AB/GUID-A6DEEA44-5EFF-3260-B003-35A6C9B0E70B"><apiname>CFbsBitmap::Compress()</apiname></xref> and <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita#GUID-683A1D42-2764-3EB7-BD19-9E12559199AB/GUID-0098D4B6-35F3-31DB-ADCE-9586601AAAFA"><apiname>CFbsBitmap::CompressInBackground()</apiname></xref>. </p> </section>

<section><title>The extended bitmap approach</title> <p>The extended bitmap

framework allows device creators to define and add their own compression formats.

Bitmaps that are created using this framework are known as <b>extended bitmaps</b>.

The Font and Bitmap Server simply stores the compressed data and does not

interpret it in any way. </p> <p>The key features of extended bitmaps are: </p> <ul>

<li id="GUID-57B99A75-79AB-50FD-BC32-E9B3D6D4D4BA"><p>They are read-only. </p> </li>

<li id="GUID-32159A2F-DEF7-562D-BAC7-0C782F292E8C"><p>They have a type, which

is unique ID (UID) that identifies the proprietary data format. </p> </li>

<li id="GUID-D972ECDE-FDDC-5518-999B-591FC22C5BE6"><p>There are no restrictions

on the data format. </p> </li>

<li id="GUID-47813A67-8550-51FB-8DFA-E911322EE9DC"><p>When an extended bitmap

cannot be decompressed for some reason, it is rendered as solid white. </p> </li>

</ul> <p>There are two ways that the bitmap can be decompressed prior to rendering.

Which one is used depends on whether the application draws the extended bitmap

by using the Window Server API (such as <xref href="GUID-0AEE5955-C530-35F1-A904-69183331B294.dita"><apiname>CWindowGc</apiname></xref>) for

on-screen rendering or the BitGDI API for off-screen rendering and Direct

Screen Access (DSA). </p> <p>To illustrate how it works, let us consider a

scenario in which extended bitmaps are used to store SVG data. (In the broadest

sense, you can consider SVG data to be a type of compression of bitmap data.)

The following diagram shows how an extended bitmap that represents an icon

is ultimately displayed on the screen. </p> <fig id="GUID-690043B5-EF70-59BB-87D4-8B0B6EEA3F31">

<title>              Example extended bitmap scenario            </title>

<image href="GUID-970A2948-5A72-5E92-84C0-86DDEE59A569_d0e261483_href.png" placement="inline"/>

</fig> <p>This is how it works: </p> <ol id="GUID-2B3B99F0-BF43-5F1C-A86E-5E9605460D7E">

<li id="GUID-77F3E86D-7FC1-5682-90C0-EE83C8C39A22"><p>An engine or server

(the Theme Server in this example) creates an extended bitmap that stores

the icon's SVG data. </p> </li>

<li id="GUID-3F46695F-DAD7-58D8-822A-18EB89A0D119"><p>To the application,

the bitmap appears like an ordinary compressed XIP ROM-based bitmap. The application

simply calls <xref href="GUID-0AEE5955-C530-35F1-A904-69183331B294.dita#GUID-0AEE5955-C530-35F1-A904-69183331B294/GUID-1A360BAF-D2EF-3D96-8E6A-C399631EFBB9"><apiname>CWindowGc::DrawBitmap()</apiname></xref> in the normal way,

passing in the <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> handle. (Applications should

not inspect the data inside the bitmap.) </p> </li>

<li id="GUID-557E0CDF-6B80-5D9F-B64B-2CA6571F7474"><p>The Window Server passes

the <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> handle to the <xref href="GUID-3A2785D4-6185-50C3-8D7E-5D94CD2B7C98.dita">render

stage chain</xref>. </p> </li>

<li id="GUID-7519E0F4-37FA-5B52-8060-73EE6E347C89"><p>The render stage identifies

the bitmap as an extended bitmap, interprets the SVG data and generates the

pixel data that is ultimately displayed on the screen. </p> </li>

</ol> <p>The internal steps are different when an application uses the BitGDI

API to draw the bitmap—for example, when an application draws the bitmap to

an off-screen bitmap by using the BitGDI graphic context class, <xref href="GUID-4A501086-7EFF-376D-8901-6D9B2EB4EFF2.dita"><apiname>CFbsBitGc</apiname></xref>.

For this to work, the device creator must provide an extended bitmap rasterizer

DLL that converts the compressed data to pixel data. However, this is also

transparent to the application. </p> <p>Extended bitmaps have the following

advantages: </p> <ul>

<li id="GUID-BAF6B974-AD40-58C2-AF10-9A9A894F8AAB"><p>Existing applications

can use extended bitmaps without modification. </p> </li>

<li id="GUID-33427210-B60D-55C0-BB00-02BE2559FD56"><p>Extended bitmaps provide

a mechanism for using compressed formats (such as vector data) that are much

more compact than raster data. This is an important consideration for high

screen resolutions. </p> </li>

</ul> </section>

<section><title>Architecture</title><p>The following diagram shows the main

participants in the extended bitmap framework. It is the device creator's

responsibility to provide appropriate support for the extended

bitmap format in the render stage and a suitable extended bitmap rasterizer

DLL, if support for drawing the extended bitmap through the BitGDI API is

required.</p><fig id="GUID-3A965E47-106D-4EC3-BCFA-E2D40EDB2647">

<title>The main participants in the extended bitmap framework, showing the

dependencies </title>

<image href="GUID-A67FFE7B-9573-543B-B3EA-0539278FE4AB_d0e261563_href.png" placement="inline"/>

</fig><p>Although it is not possible to have more than one extended bitmap

rasterizer DLL on a device, an extended bitmap rasterizer DLL can support

more  than one type of proprietary data. Similarly, support for multiple data

formats can be added to render stages.</p><p> The data format can be identified

from the type UID. When you implement  the extended bitmap feature in a device,

you must obtain UIDs for the format(s) that you want to support from Symbian

Signed in the normal way. </p><p>The Symbian platform does not define any

compression formats apart from those that are supported natively. It therefore

does not provide an implementation of an extended bitmap rasterizer. However,

it does provide a stub implementation and an example implementation, which

device creators can  use as a reference when creating their own extended bitmap

rasterizers.</p></section>

<section><title>Related APIs</title> <p>This section summarizes the extended

bitmap APIs. Note that the extended bitmap feature is new in Symbian^3. </p> <p><b>TBitmapfileCompression </b> </p> <p>The <xref href="GUID-6E40B867-F7C6-35EA-8C6F-F54AB11BDD6E.dita"><apiname>TBitmapfileCompression</apiname></xref> enum has a new value, <codeph>EProprietaryCompression</codeph>, which represents

an extended bitmap. </p> <p><b>CFbsBitmap </b> </p> <p>The following table

provides a summary of the new <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> functions that

provide support for extended bitmaps. </p> <table id="GUID-7CF90E7D-1908-50FB-84AB-36F04B04E2DF">

<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

<thead>

<row>

<entry>Function</entry>

<entry>Description</entry>

</row>

</thead>

<tbody>

<row>

<entry><p> <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita#GUID-683A1D42-2764-3EB7-BD19-9E12559199AB/GUID-F2AAAC53-3D74-3C9F-B275-58BD5FF81C85"><apiname>CFbsBitmap::CreateExtendedBitmap()</apiname></xref>  </p> </entry>

<entry><p>Creates an extended bitmap. There are two overloads of this function.

They both have a parameter for the UID of the proprietary data format. One

takes a pointer to the raw data, whereas the other takes a pointer to an initializer,

which is an implementation of the <xref href="GUID-C950A55E-B52A-3680-B897-04E7C3A7BB71.dita"><apiname>MFbsExtendedBitmapInitializer</apiname></xref> interface.

The second overload is the recommended approach because it avoids unnecessary

memory copying. </p> </entry>

</row>

<row>

<entry><p> <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita#GUID-683A1D42-2764-3EB7-BD19-9E12559199AB/GUID-9274BB13-2BE4-3B3B-A55C-2500E2FE432C"><apiname>CFbsBitmap::ExtendedBitmapType()</apiname></xref>  </p> </entry>

<entry><p>Gets the UID of the proprietary data format. Returns null if it

is not an extended bitmap. </p> </entry>

</row>

<row>

<entry><p> <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita#GUID-683A1D42-2764-3EB7-BD19-9E12559199AB/GUID-BF789218-A647-3D94-AF56-05265C45F7E7"><apiname>CFbsBitmap::DataSize()</apiname></xref>  </p> </entry>

<entry><p>Returns the size in bytes of the data stored in the bitmap. For

an extended bitmap this is the size of the proprietary data (not the size

of the rasterized pixel data). </p> </entry>

</row>

</tbody>

</tgroup>

</table> <p>Here is a code snippet that shows how a content provider can create

an extended bitmap: </p> <codeblock id="GUID-4511B5FF-1A17-5B8B-8471-C6F696D049F3" xml:space="preserve">const TUid KUidMyProprietaryFormat = { &lt;UID in hex&gt; };

const TSize KSize(640, 480);

const TInt KDataSize = 100;

// Only needed if not connected to the Window Server.

User::LeaveIfError(RFbsSession::Connect());

CFbsBitmap* bmp = new(ELeave) CFbsBitmap();

CleanupStack::PushL(bmp);

MFbsExtendedBitmapInitializer* initializer = GetMyInitializerL();

User::LeaveIfError(bmp->CreateExtendedBitmap(KSize, EColor16MAP, KUidMyProprietaryFormat, 

                                             KDataSize, *initializer));</codeblock> <p>The

following <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> functions provide support for extended

bitmaps, provided a suitable extended bitmap rasterizer DLL is available: </p> <ul>

<li id="GUID-6ABAA42C-1270-5F5C-9D4E-7F1750C05659"><xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita#GUID-683A1D42-2764-3EB7-BD19-9E12559199AB/GUID-838CF3C5-C513-33B7-9C81-0EBCE075F6B7"><apiname>CFbsBitmap::GetPixel()</apiname></xref> </li>

<li id="GUID-876BA701-AE33-515F-8756-6052A37991F8"><xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita#GUID-683A1D42-2764-3EB7-BD19-9E12559199AB/GUID-D24300BA-20D7-34E6-BD23-ED281A0D957E"><apiname>CFbsBitmap::GetScanLine()</apiname></xref> </li>

<li id="GUID-152C155E-94DB-5462-80EE-AF409C001B49"><xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita#GUID-683A1D42-2764-3EB7-BD19-9E12559199AB/GUID-57BC8EB1-B9F4-39A9-A18B-594CFB7786B6"><apiname>CFbsBitmap::GetVerticalScanLine()</apiname></xref> </li>

</ul> <p>It is possible to access the proprietary data inside an extended

bitmap by calling the <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita#GUID-683A1D42-2764-3EB7-BD19-9E12559199AB/GUID-2AB943ED-7DBE-3FDA-82AF-317F152EDB03"><apiname>CFbsBitmap::DataAddress()</apiname></xref> function.

For example, the render stage that decompresses the extended bitmap makes

use of this function. Note that clients must not modify the proprietary data. </p> <p><b>CFbsRasterizer </b> </p> <p>This

is an interface for which the extended bitmap rasterizer DLL must provide

an implementation. See <xref href="GUID-E6E6A439-B3CC-5FEA-9148-2DB5F37003F2.dita">Creating

an Extended Bitmap Rasterizer</xref> for more information. </p> </section>

</conbody><related-links>

<link href="GUID-E6E6A439-B3CC-5FEA-9148-2DB5F37003F2.dita"><linktext> Creating

an Extended Bitmap Rasterizer</linktext></link>

<link href="GUID-3A2785D4-6185-50C3-8D7E-5D94CD2B7C98.dita"><linktext>Render Stages</linktext>

</link>

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

Bitmap Server Overview</linktext></link>