Transparent: Drawing Transparent Windows

This example application demonstrates how to implement the following window server features using the RWindow::BeginRedraw() and RWindow::EndRedraw() functions:

• creating transparent, non-transparent and blank windows,

• changing the transparency of a window,

• drawing content on a window.

This example is located in the examples\Graphics\WS\transparent folder. The following sections provide more information about this example application.

This example creates a blank window on which a background and a foreground window are drawn. The blank window is constructed using the RBlankWindow class. The CPeriodic class triggers periodic redraws on the window. The following functions are used to re-draw content on the window:

• RWindow::Invalidate()

• RWindow::BeginRedraw()

• RWindow::EndRedraw()

• RWindow::Activate()

The transparency of the foreground window is changed using the following functions:

• RWindow::SetTransparencyFactor(): The transparency factor of the foreground window is incremented from 0 to 255 (transparent to opaque) using this function.

• RWindow::SetTransparentRegion(): The transparent region is moved on the foreground window by changing the offset of the transparent region using this function.

• RWindow::SetTransparencyBitmap(): The transparency bitmap of the transparent window is changed based on the bitmap mask using this function. This bitmap mask is created using the CFbsBitmap class. The bitmap mask contains some content drawn on it using the CBitmapDevice and CBitmapGc classes.

The user-defined class CEventHandler handles pointer events when transparent areas of the window are clicked on by the pointer device. An appropriate message is displayed when a click event is detected.

The following principal classes are used in this example application:

• CPeriodic

• RWindowGroup

• RBlankWindow

• RWindow

• RWsSession

• CWsScreenDevice

• CWindowGc

• CFbsBitmap

• CFbsBitmapDevice

• CFbsBitGc

• TRegionFix

• TWsEvent

The Symbian OS build process describes how to build this example.

The Transparent builds an executable called transparent.exe in the standard location (\epoc32\release\winscw\<build_variant> for Carbide).