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+<?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-02BD38E7-A579-5BD5-9444-4E7C14C7809A" xml:lang="en"><title>Transparent
+Windows</title><shortdesc>This topic introduces the window transparency feature, which you
+can use to create semi-transparent UI content over other UI content. In ScreenPlay
+you can also use transparent windows to create semi-transparent UI content
+over external content, such as video and OpenGL ES. For example, in ScreenPlay
+you can display a semi-transparent dialog box over an OpenGL ES game. Transparent
+windows are implemented using alpha compositing, which means that the transparency
+information is embedded within the drawing commands. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p> <i>Note</i>: Semi-transparent UI content over content provided by Direct
+Screen Access (DSA) has never been supported and ScreenPlay does not change
+this. </p>
+<p> <b>Variant</b>: ScreenPlay and non-ScreenPlay. <b>Target audience</b>:
+Application developers. </p>
+<section><title>Alpha compositing</title> <p>In alpha compositing, an alpha
+channel is used to store opacity information along with the color values for
+each pixel. For example, if the color is represented as RGB values, the pixel
+values are typically stored as RGBA, where the final value is the alpha value.
+This represents the percentage opacity. Like the RGB values, the alpha value
+is frequently expressed in the range of 0 (completely transparent) to 255
+(fully opaque). For example, (0, 0, 0, 0) represents fully transparent black
+and (255, 255, 255, 127) represents white that has 50% opacity. </p> <p>Each
+of the RGB values are multiplied by the alpha percentage to give the opacity
+of the pixel. In order to reduce the need for multiplication during the compositing
+process, the RGB values are sometimes multiplied by the alpha value before
+storage. This is known as <b>premultiplied alpha</b> format. For example,
+a premultiplied alpha representation of white that has 50% opacity is (127,
+127, 127, 127). </p> </section>
+<section><title>Enabling transparency</title> <p>To enable transparency, call
+the <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow::SetTransparencyAlphaChannel()</apiname></xref> method
+on the window (which must be an <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref> type)
+before it is activated. The transparency is then determined by the alpha values
+of the content rendered to the window. Typically you set the background to
+be fully or partially transparent, as shown in the following example: </p> <codeblock id="GUID-C33B91C2-D83C-5A6D-91A5-AB29B8EF46A0" xml:space="preserve">// Set transparency mode on.
+iWindow.SetTransparencyAlphaChannel();
+    
+// Set the background to be fully transparent black.
+iWindow.SetBackgroundColor(TRgb(0,0,0,0)); 
+    
+// Activate the window.
+iWindow.Activate();
+    
+// Begin drawing to the window.
+...  </codeblock></section>
+<section><title>Note</title><p>In earlier versions of the Symbian
+platform, it was possible to create transparent windows using a mask and the <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref> class's <codeph>SetTransparencyFactor()</codeph>, <codeph>SetTransparencyBitmap()</codeph> and <codeph>SetTransparencyWsBitmap()</codeph> methods. <b>This mechanism is now deprecated and these methods are no longer
+functional</b>.</p><p>A new application and UI framework is planned for Symbian^4
+(S^4). In order for AVKON applications (and clients that draw using <xref href="GUID-5FAF3401-9EC6-3411-9AB3-BBDB4A448C65.dita"><apiname>CWindowGC</apiname></xref>)
+to work correctly on this new framework, the main view must be opaque. See <xref href="GUID-29272C8D-A0F6-4861-90FB-D1637D0D8CD8.dita">How will the New Application
+Architecture Affect my Applications?</xref> for more information.</p> </section>
+</conbody><related-links>
+<link href="GUID-99AE1D62-571A-5A63-B472-C0FBC0861F52.dita"><linktext>Window Types</linktext>
+</link>
+<link href="GUID-29272C8D-A0F6-4861-90FB-D1637D0D8CD8.dita"><linktext>How will
+the New Application Architecture Affect my Applications?</linktext></link>
+</related-links></concept>
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