<?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-37393245-6AA1-528F-A5C1-EC114779791E" xml:lang="en"><title>Screen

Driver Graphics Acceleration Support</title><shortdesc>This topic introduces the 2D graphics hardware acceleration support

provided by the Screen Driver component. This is generally used only in the

non-ScreenPlay variant, because ScreenPlay provides better alternatives for

implementing support for graphics acceleration hardware. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p> <b>Variant</b>: <xref href="GUID-F64E6551-670E-5E12-8103-DE504D3EC94F.dita">Non-ScreenPlay</xref>. <b>Target

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

<p>2D graphics acceleration enables improved performance for multimedia applications.

The Screen Driver component provides an API for hardware acceleration. This

is defined in <filepath>graphicsaccelerator.h</filepath> and is abstract.

The abstract base class for all accelerators is <xref href="GUID-26AD7E66-3C68-308D-9612-98438622FAC9.dita"><apiname>CGraphicsAccelerator</apiname></xref>.

The API also defines a set of common 2D graphics operations that are capable

of being accelerated in hardware (by a separate graphics processor), or in

software (by a DLL that optimizes the algorithms for particular devices and

display modes). The API may or may not be implemented by device creators. </p>

<p>Note that graphics acceleration, if implemented in the Screen Driver component,

is designed to be used transparently within <xref href="GUID-EAAD1719-C02C-5705-A5C3-993E36441BE6.dita">BitGDI</xref>,

not called explicitly by clients. </p>

<section><title>Architectural relationships</title> <p>The Screen Driver API

for 2D graphics hardware acceleration is closely related to the following: </p> <ul>

<li id="GUID-6BCB5C4E-1D79-5E40-9E5D-0AE96D9E2524"><p><xref href="GUID-B6D4AEE9-5C17-51D9-BBDE-7CCB5218279D.dita">GDI</xref>.

The graphics acceleration support that is provided by the Screen Driver component

is integrated into the underlying implementation of the GDI API. Applications

do not need to be aware of whether or not a particular graphics operation

is accelerated. If an accelerated implementation of a function is available,

it is used in preference to the generic algorithm. </p> </li>

<li id="GUID-A670E135-AAF3-55DB-A2F6-DF519B71A434"><p><xref href="GUID-EAAD1719-C02C-5705-A5C3-993E36441BE6.dita">BitGDI</xref>.

Software graphics accelerators can draw to standard bitmaps (the <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> class),

as well as hardware bitmaps (represented by the <xref href="GUID-DE8E21D9-FF93-358D-A479-F84435DBECAD.dita"><apiname>RHardwareBitmap</apiname></xref> class).

However, hardware graphics accelerators can only draw to hardware bitmaps. </p> </li>

</ul> </section>

<section><title>Description</title> <p>Each class derived from <xref href="GUID-B741084F-D353-3298-9F97-2F93DF5B2CE3.dita"><apiname>TGraphicsOperation</apiname></xref> represents

a different accelerated graphics operation. The subset of these operations

supported by an accelerator is hardware-dependent and varies from device to

device. The graphics accelerator's capabilities can be queried before it is

used. The <xref href="GUID-EAA3593A-95E4-33BC-A43D-AC1E9E354245.dita"><apiname>TGraphicsAcceleratorCaps</apiname></xref> class gives some of

the capabilities, for instance whether mask bitmaps must be in a certain display

mode. To find out whether a particular operation is supported, an attempt

should be made to execute it. Unsupported functions should simply return <codeph>KErrNotSupported</codeph>.

The user of the API does not need to be aware of whether an operation is accelerated

in hardware or in software—the API is the same for both. </p> <p>The types

of accelerated operations that are enabled by this API include: </p> <ul>

<li id="GUID-BB4A305D-5EA2-56B9-8F9E-78F6A8669CAA"><p>filling a rectangle

with a color or pattern; fading and inverting colors </p> </li>

<li id="GUID-6A4EDF8C-6C0F-52A8-98F0-F26083A4A2F1"><p>a variety of bitblt

operations, including using a mask, transparency or alpha blending. These

operations may involve scaling the bitmap </p> </li>

<li id="GUID-4F5086F2-1886-5E1D-87F1-30106EC7C82F"><p>filling a polygon with

a color or a pattern. </p> </li>

</ul> <p>All of these operations may optionally take place within a clipping

region. </p> <p>Hardware graphics acceleration can only draw to hardware bitmaps.

These are bitmaps that are stored in a static, contiguous area of physical

memory that is accessible to both the CPU and a separate graphics processor.

The interface to a hardware bitmap is the class <xref href="GUID-DE8E21D9-FF93-358D-A479-F84435DBECAD.dita"><apiname>RHardwareBitmap</apiname></xref>.

Software graphics acceleration can write to both <codeph>CFbsBitmap</codeph> s

and <codeph>RHardwareBitmap</codeph> s. </p> </section>

<section><title>Limitations</title> <p>The Screen Driver provides a synchronous

API for the implementation of hardware acceleration. This means that although

each operation may execute faster than within a software implementation, the

calling thread on the CPU must wait for each GPU operation to complete. This

can cause significant delay within the context of the Window Server. In addition,

graphics acceleration hardware is generally designed to accept a pipeline

of instructions rather than the individual instructions provided by the Screen

Driver. The Screen Driver's one-by-one approach causes greater latency than

could be achieved using a pipeline approach. These limitations are part of

the rationale for the introduction of the <xref href="GUID-D93978BE-11A3-5CE3-B110-1DEAA5AD566C.dita">ScreenPlay

architecture</xref>. </p> </section>

</conbody><related-links>

<link href="GUID-F64E6551-670E-5E12-8103-DE504D3EC94F.dita"><linktext>The Non-ScreenPlay

Architecture</linktext></link>

<link href="GUID-9E7D563E-9FFB-5FA9-8944-9CBAC281FDD2.dita"><linktext>Screen Driver

Component</linktext></link>

<link href="GUID-E9FF94D2-AFFD-54A4-A6C2-00929BC70DB0.dita"><linktext>BitGDI Concepts</linktext>

</link>

<link href="GUID-0AB9B221-38AE-576E-AC5A-C4C106E3D93B.dita"><linktext>GDI Overview</linktext>

</link>

</related-links></concept>