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<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>