Class CDirectScreenAccess

class CDirectScreenAccess : public CActive;

Description

An active object used to start direct screen access.

Direct screen access is a way of drawing to the screen without using the window server. As this avoids client-server communication, it is much faster, and may be useful for games and video. Note that some interaction with the window server is needed in order to prevent the application from drawing over other application's data.

The object's (private) RunL() function is called by the window server in order to abort direct screen access. This might occur when another window needs to be displayed in front or when the window with direct screen access is moved. The active object's priority is RDirectScreenAccess::EPriorityVeryHigh so that direct screen access will be aborted as quickly as possible.

Derivation

• CBase - Base class for all classes to be instantiated on the heap

• CActive - The core class of the active object abstraction

• CDirectScreenAccess - An active object used to start direct screen access

Members

Defined in CDirectScreenAccess:
DoCancel(), DrawingRegion(), Gc(), NewL(), RunL(), ScreenDevice(), StartL()

Inherited from CActive:
Cancel(), Deque(), EPriorityHigh, EPriorityIdle, EPriorityLow, EPriorityStandard, EPriorityUserInput, Extension_(), IsActive(), IsAdded(), Priority(), RunError(), SetActive(), SetPriority(), TPriority, iStatus

Inherited from CBase:
Delete(), operator new()

static IMPORT_C CDirectScreenAccess *NewL(RWsSession &aWs, CWsScreenDevice &aScreenDevice, RWindowBase &aWin, MDirectScreenAccess &aAbort);

Description

Allocates and constructs the object and adds it to the current active scheduler.

This function always causes a flush of the window server buffer.

Parameters

RWsSession &aWs A session with the window server. CWsScreenDevice &aScreenDevice Specifies the characteristics of the screen device to draw to. RWindowBase &aWin The window to draw to directly. MDirectScreenAccess &aAbort Defines an AbortNow() and a Restart() function which are both called on aborting, as part of the RunL(). Restart() is called from an idle time active object (CIdle).

Return value

CDirectScreenAccess * The newly constructed object.

IMPORT_C void StartL();

Description

Informs the window server that you are going to start direct screen access and sets up a graphics context with which you can draw to the screen.

It should also be called to restart direct screen access after Cancel() has been called to stop it.

While the DSA is in operation, it is strongly advised that the client should not make any call to WSERV that will affect the visible area of the window in which the DSA is taking place.

When WSERV tells the client that it needs to abort its DSA, it waits to receive the acknowledgment from the client that it has done so. However, it doesn't wait for ever, since the client may have entered some long running calculation or even an infinite loop. So WSERV also waits on a timer: if the timer expires before the client acknowledges, then WSERV continues; if, later on, WSERV gets notification from the client that it has aborted the DSA, then WSERV will invalidate the region in which the DSA was taking place, just in case there had been a conflict between the DSA and another client.

This function always causes a flush of the window server buffer.

inline CFbsBitGc *Gc();

Description

Gets the graphics context for drawing to the screen.

This is set up by calling StartL(). Its origin is set so that you should use window coordinates to specify which part of the screen to draw to and its clipping region is set to the visible part of the window.

Code built to run on the Emulator must call CFbsScreenDevice::Update() in order to see the results of drawing to this graphics context, but this may not be required on all target hardware.

Return value

CFbsBitGc * The graphics context for drawing to the screen.

inline CFbsScreenDevice *&ScreenDevice();

Description

Gets the screen device to draw to.

You should not use this screen device to create fonts because the object is deleted and recreated when direct screen access is aborted and restarted. Instead, create and use your own CFbsScreenDevice object to create fonts.

Return value

CFbsScreenDevice *& The target screen device.

inline RRegion *DrawingRegion();

Description

Gets the clipping region to draw to.

You must not draw outside of this region.

The clipping region is calculated when StartL() is called, and is only updated if StartL() is called again.

The region is specified in screen coordinates. This can be useful if you need to reapply the clipping region to the graphics context (CFbsBitGc::SetClippingRegion()).

Return value

RRegion * The clipping region to draw to.

private: virtual void DoCancel();

Description

Implements cancellation of an outstanding request.

This function is called as part of the active object's Cancel().

It must call the appropriate cancel function offered by the active object's asynchronous service provider. The asynchronous service provider's cancel is expected to act immediately.

DoCancel() must not wait for event completion; this is handled by Cancel().

private: virtual void RunL();

Description

Handles an active object's request completion event.

A derived class must provide an implementation to handle the completed request. If appropriate, it may issue another request.

The function is called by the active scheduler when a request completion event occurs, i.e. after the active scheduler's WaitForAnyRequest() function completes.

Before calling this active object's RunL() function, the active scheduler has:

1. decided that this is the highest priority active object with a completed request

2. marked this active object's request as complete (i.e. the request is no longer outstanding)

RunL() runs under a trap harness in the active scheduler. If it leaves, then the active scheduler calls RunError() to handle the leave.

Note that once the active scheduler's Start() function has been called, all user code is run under one of the program's active object's RunL() or RunError() functions.