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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-02BD38E7-A579-5BD5-9444-4E7C14C7809A" xml:lang="en"><title>Transparent

    13 Windows</title><shortdesc>This topic introduces the window transparency feature, which you

    14 can use to create semi-transparent UI content over other UI content. In ScreenPlay

    15 you can also use transparent windows to create semi-transparent UI content

    16 over external content, such as video and OpenGL ES. For example, in ScreenPlay

    17 you can display a semi-transparent dialog box over an OpenGL ES game. Transparent

    18 windows are implemented using alpha compositing, which means that the transparency

    19 information is embedded within the drawing commands. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    20 <p> <i>Note</i>: Semi-transparent UI content over content provided by Direct

    21 Screen Access (DSA) has never been supported and ScreenPlay does not change

    22 this. </p>

    23 <p> <b>Variant</b>: ScreenPlay and non-ScreenPlay. <b>Target audience</b>:

    24 Application developers. </p>

    25 <section id="GUID-7208D287-D0D9-4E19-89F0-87DB9BCE4736"><title>Alpha compositing</title> <p>In alpha compositing, an alpha

    26 channel is used to store opacity information along with the color values for

    27 each pixel. For example, if the color is represented as RGB values, the pixel

    28 values are typically stored as RGBA, where the final value is the alpha value.

    29 This represents the percentage opacity. Like the RGB values, the alpha value

    30 is frequently expressed in the range of 0 (completely transparent) to 255

    31 (fully opaque). For example, (0, 0, 0, 0) represents fully transparent black

    32 and (255, 255, 255, 127) represents white that has 50% opacity. </p> <p>Each

    33 of the RGB values are multiplied by the alpha percentage to give the opacity

    34 of the pixel. In order to reduce the need for multiplication during the compositing

    35 process, the RGB values are sometimes multiplied by the alpha value before

    36 storage. This is known as <b>premultiplied alpha</b> format. For example,

    37 a premultiplied alpha representation of white that has 50% opacity is (127,

    38 127, 127, 127). </p> </section>

    39 <section id="GUID-ED7D01C9-6B18-4280-B44E-B62ADE9EBA90"><title>Enabling transparency</title> <p>To enable transparency, call

    40 the <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow::SetTransparencyAlphaChannel()</apiname></xref> method

    41 on the window (which must be an <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref> type)

    42 before it is activated. The transparency is then determined by the alpha values

    43 of the content rendered to the window. Typically you set the background to

    44 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.

    45 iWindow.SetTransparencyAlphaChannel();

    46     

    47 // Set the background to be fully transparent black.

    48 iWindow.SetBackgroundColor(TRgb(0,0,0,0)); 

    49     

    50 // Activate the window.

    51 iWindow.Activate();

    52     

    53 // Begin drawing to the window.

    54 ...  </codeblock></section>

    55 <section id="GUID-66EBABCC-4BF4-4DE8-9AD3-27598F3A0025"><title>Note</title><p>In earlier versions of the Symbian platform,

    56 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

    57 mechanism is now deprecated and these methods are no longer functional</b>.</p><p>A

    58 new application and UI framework is planned for Symbian^4 (S^4). In order

    59 for AVKON applications (and clients that draw using <xref href="GUID-0AEE5955-C530-35F1-A904-69183331B294.dita"><apiname>CWindowGc</apiname></xref>)

    60 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

    61 Architecture Affect my Applications?</xref> for more information.</p> </section>

    62 </conbody><related-links>

    63 <link href="GUID-99AE1D62-571A-5A63-B472-C0FBC0861F52.dita"><linktext>Window Types</linktext>

    64 </link>

    65 <link href="GUID-29272C8D-A0F6-4861-90FB-D1637D0D8CD8.dita"><linktext>How will

    66 the New Application Architecture Affect my Applications?</linktext></link>

    67 </related-links></concept>