Drawing to the screen outside application framework

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Created: symbianyucca (04 Apr 2007)

Last edited: hamishwillee (18 Sep 2012)

The CWindowDrawer class illustrates how to construct a drawable screen outside the standard application framework. You usually use this kind of code when constructing a background server that normally needs to be hidden and only requires an UI in some parts of its operations.

As with this example the CWindowDrawer will not take focus which means that the current focused application still receives all key input. To disable this call the EnableReceiptOfFocus() method with ETrue.

For key catching you can also use CKeyCapturer

The active object implementation used in this example uses RWsSession's RedrawReady() method to receive redraw events. To get your own drawing code into it you only need to change the content of the Draw() method.

Also if you don't want to take the whole screen for your window you can change the values given in iWindow's SetExtent() method inside the ConstructL() method.

Library required:

LIBRARY gdi.lib  //CFont
LIBRARY ws32.lib //RWindowGroup ,CWsScreenDevice, CWindowGc
LIBRARY apgrfx.lib //CApaWindowGroupName

WindowDrawer.cpp

#include <apgwgnam.h> //CApaWindowGroupName
#include "WindowDrawer.h"
#include <coedef.h> //for ECoeWinPriorityAlwaysAtFront
 
CWindowDrawer* CWindowDrawer::NewL(void)
	{
	CWindowDrawer* self = CWindowDrawer::NewLC(void);
	CleanupStack::Pop(self);
	return self;
	}
 
 
CWindowDrawer* CWindowDrawer::NewLC(void)
	{
	CWindowDrawer* self = new (ELeave) CWindowDrawer(void);
	CleanupStack::PushL(self);
	self->ConstructL();
	return self;
	}
 
// the active object priority should be relatively low
CWindowDrawer::CWindowDrawer(void):CActive(EPriorityLow)
{
}
 
CWindowDrawer::~CWindowDrawer()
{	
	Cancel();
 
	if(iMyFont)
	{
		iScreenDevice->ReleaseFont(iMyFont);
		iMyFont = NULL;
	}
 
	delete iWindowGc;
	iWindowGc = NULL;
	delete iScreenDevice;
	iScreenDevice = NULL;
 
	iWindow.Close();
 
	iWindowGroup.Close();
	iWsSession.Close();
}
 
void CWindowDrawer::ConstructL(void)
{
	CActiveScheduler::Add(this);
 
	User::LeaveIfError(iWsSession.Connect());
 
	iScreenDevice=new (ELeave) CWsScreenDevice(iWsSession);
	User::LeaveIfError(iScreenDevice->Construct());
	User::LeaveIfError(iScreenDevice->CreateContext(iWindowGc));
 
	TFontSpec MyeFontSpec (KFontArial, 12*15);	
	MyeFontSpec.iTypeface.SetIsProportional(ETrue);
	User::LeaveIfError(iScreenDevice->GetNearestFontInTwips(iMyFont,MyeFontSpec));
 
	iWindowGroup=RWindowGroup(iWsSession);
	User::LeaveIfError(iWindowGroup.Construct((TUint32)&iWindowGroup, EFalse));
//	iWindowGroup.SetOrdinalPosition(0,ECoeWinPriorityNormal);
	iWindowGroup.SetOrdinalPosition(0,ECoeWinPriorityAlwaysAtFront);
	iWindowGroup.EnableReceiptOfFocus(EFalse);
 
	CApaWindowGroupName* winGroupName=CApaWindowGroupName::NewLC(iWsSession);
	winGroupName->SetHidden(ETrue);
	winGroupName->SetWindowGroupName(iWindowGroup);
	CleanupStack::PopAndDestroy();
 
	iWindow=RWindow(iWsSession);
	User::LeaveIfError(iWindow.Construct(iWindowGroup, (TUint32)&iWindow));
 
	TPixelsTwipsAndRotation SizeAndRotation;
	iScreenDevice->GetDefaultScreenSizeAndRotation(SizeAndRotation);
 
	iWindow.Activate();
	iWindow.SetExtent(TPoint(0,0),SizeAndRotation.iPixelSize);
	iWindow.SetBackgroundColor(KRgbBlue);
//	iWindow.SetOrdinalPosition(0,ECoeWinPriorityNormal);
	iWindow.SetOrdinalPosition(0, ECoeWinPriorityAlwaysAtFront);
	iWindow.SetNonFading(ETrue);	
	iWindow.SetVisible(ETrue);		
 
	Draw();
	iWsSession.RedrawReady(&iStatus);
	SetActive();
}
 
void CWindowDrawer::RunL()
{
	if (iStatus != KErrCancel) 
	{
		TWsRedrawEvent e;
		iWsSession.GetRedraw(e);
 
		// if Windows Server does not want a redraw the window handle is 0
		if (e.Handle() != 0)
			{
			// draw our only window
			Draw();
			}
 
		iWsSession.RedrawReady(&iStatus);
		SetActive();
	}
}
 
void CWindowDrawer::Draw(void)
{
	iWindowGc->Activate(iWindow);
 
	TRect DrwRect(TPoint(0,0), iWindow.Size());
 
	iWindow.Invalidate(DrwRect);
	iWindow.BeginRedraw();
	iWindowGc->Clear(DrwRect); 
 
	if(iMyFont)
	{
		iWindowGc->UseFont(iMyFont);
 
		TInt StartY ((DrwRect.Height() - iMyFont->HeightInPixels()) / 2);
 
		iWindowGc->DrawText(KtxHelloThere,TRect(0,StartY,DrwRect.Width(),(StartY + iMyFont->HeightInPixels())),iMyFont->AscentInPixels(), CGraphicsContext::ECenter, 0);
	}
 
	iWindow.EndRedraw();
 
	iWindowGc->Deactivate();
	iWsSession.Flush();
}
 
void CWindowDrawer::DoCancel()
{
	iWsSession.RedrawReadyCancel();
}

WindowDrawer.h

#include <gdi.h> // CFont
#include <w32std.h> //RWindowGroup, CWsScreenDevice, CWindowGc
 
_LIT(KtxHelloThere			,"Hi there !");
_LIT(KFontArial				,"Arial");
 
class CWindowDrawer : public CActive
{
public:
	static CWindowDrawer* NewL(void);
	static CWindowDrawer* NewLC(void);
	~CWindowDrawer();
protected:
	void DoCancel();
	void RunL();
private:
	CWindowDrawer();
	void ConstructL(void);
	void Draw(void);
private:
	RWsSession 			iWsSession; 
	CWindowGc* 			iWindowGc;
	CWsScreenDevice* 	iScreenDevice;
	RWindowGroup 		iWindowGroup; 
	RWindow 			iWindow; 
	CFont*				iMyFont;
};

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