Transparent -Windows

Transparent -WindowsThis 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. -

Note: Semi-transparent UI content over content provided by Direct -Screen Access (DSA) has never been supported and ScreenPlay does not change -this.

Variant: ScreenPlay and non-ScreenPlay. Target audience: -Application developers.

Alpha compositing

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.

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 premultiplied alpha format. For example, -a premultiplied alpha representation of white that has 50% opacity is (127, -127, 127, 127).

Enabling transparency

To enable transparency, call -the RWindow::SetTransparencyAlphaChannel() method -on the window (which must be an RWindow 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:

// 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. -...

Note

In earlier versions of the Symbian platform, -it was possible to create transparent windows using a mask and the RWindow class's SetTransparencyFactor(), SetTransparencyBitmap() and SetTransparencyWsBitmap() methods. This -mechanism is now deprecated and these methods are no longer functional.

A -new application and UI framework is planned for Symbian^4 (S^4). In order -for AVKON applications (and clients that draw using CWindowGc) -to work correctly on this new framework, the main view must be opaque. See How will the New Application -Architecture Affect my Applications? for more information.

-Window Types - -How will -the New Application Architecture Affect my Applications? + + + + + +Transparent +WindowsThis 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. +

Note: Semi-transparent UI content over content provided by Direct +Screen Access (DSA) has never been supported and ScreenPlay does not change +this.

Variant: ScreenPlay and non-ScreenPlay. Target audience: +Application developers.

Alpha compositing

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.

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 premultiplied alpha format. For example, +a premultiplied alpha representation of white that has 50% opacity is (127, +127, 127, 127).

Enabling transparency

To +enable transparency, call the RWindow::SetTransparencyAlphaChannel() method +on the window (which must be an RWindow 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:

// 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. +...

Note

In +earlier versions of the Symbian platform, it was possible to create transparent +windows using a mask and the RWindow class's SetTransparencyFactor(), SetTransparencyBitmap() and SetTransparencyWsBitmap() methods. This mechanism +is now deprecated and these methods are no longer functional.

A +new application and UI framework is planned for Symbian^4 (S^4). In order +for AVKON applications (and clients that draw using CWindowGc) +to work correctly on this new framework, the main view must be opaque. See How will the New Application +Architecture Affect my Applications? for more information.

+Window Types + +How will +the New Application Architecture Affect my Applications? +Drawing transparent +windows example

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