Window +Surface Implementation

Target audience: Device creators.

Symbian windows

Window surfaces are created by +the eglCreateWindowSurface() function, to which is passed +a handle to a window provided by the Symbian Window +Server. Key Window Server classes include the following:

RWindow, +which is a handle to a standard window.
RWsSession, +which is the Window Server session class. This is required to create Window +Server objects.
CWsScreenDevice, +which is a Window Server client-side object representing the screen.

Non-ScreenPlay

In the non-ScreenPlay variant +there is no composition engine and both Symbian API drawing (for example, +through CWindowGc) and EGL client API drawing are rendered +to a single display. The EGL implementation can achieve this in a number of +ways, including:

Using Direct Screen +Access (DSA) to render the EGL client API drawing directly to the screen. +This is done in cooperation with the Window Server, which provides clipping +instructions. This approach is particularly suitable when graphics acceleration +hardware is available.
Rendering the EGL client +API drawing to an offscreen CFbsBitmap and then calling +a Window Server API to blit the CFbsBitmap onto the screen, +with any necessary clipping.

ScreenPlay

ScreenPlay has introduced the Graphics Composition Collection, +which enables a number of surfaces to be arranged in layers and to +be composed together to produce the final output on the display. In this section, +these surfaces are called composition surfaces in order to distinguish +them from EGL surfaces. Each composition surface is mapped to memory, which +can be specialized graphics memory for faster performance.

All +Window Server drawing (such as the application UI) is rendered to a composition +surface called the UI surface, which is usually the topmost layer and +can be semi-transparent.

When the EGL implementation creates an EGL +window surface for a Symbian window (represented by RWindow), +the EGL implementation must do the following:

Create a new composition +surface with the same width and height as the RWindow.
Position the composition +surface in a layer below the UI layer, directly below the RWindow.
Make the RWindow transparent +in order for the composition surface to show through.

All of the EGL client API drawing to the EGL window surface +is then rendered to the composition surface and the application's UI appears +as a semi-transparent layer above it.

When a window is resized, a new +composition surface needs to be created with the new width and height, and +positioned as a layer below the RWindow in place of the +previous composition surface.

A composition surface can have more than +one pixel buffer associated with it (each buffer has the same dimensions). +For an EGL window surface, the composition surface should have two buffers +for double-buffered drawing. This means, for example, that OpenVG commands +can draw to the back buffer, while the front buffer is being +composed to the screen.