Overview

By default a control will draw itself on the screen by the system
default Gc, but in some cases developers need it to draw itself on a
bitmap, for example when implementing transition effect of view
switching both views' screen shots are needed. The article shows how to
force some controls (derived directly or indirectly from CCoeControl)
to draw them self on a specified bitmap instead of screen.

Solution

The CCoeControl::SetGc() or CCoeControl::SetCustomGc() can be used
to redirect the control's drawing to a custom Gc, but the functions
accept a pointer to a window gc only, that means a bitmap gc can no be
used directly. The CWindowToBitmapMappingGc introduced in Symbian OS
v7.0 can be used to resolve the problem, because it can map all the
operations on a window gc to a bitmap gc.

// .mmp<br /> ...<br /> // begin by chen<br /> LIBRARY egul.lib // CWindowToBitmapMappingGc<br /> LIBRARY bitgdi.lib // CFbsBitmapDevice<br /> LIBRARY imageconversion.lib // CImageEncoder<br /> // end by chen<br /> ...<br /> // .cpp<br /> ...<br /> // begin by chen<br /> #include <gulgcmap.h> // CWindowToBitmapMappingGc<br /> #include <ImageConversion.h> // CImageEncoder<br /> // end by chen<br /> ...<br /> TBool CGoodbyeHellAppUi::HandleDummyDrawNowMenuItemSelectedL( TInt aCommand )<br /> {<br /> // TODO: implement selected event handler<br /> // begin by chen<br /> RFs& fs = iCoeEnv->FsSession();<br /> CCoeControl* control = iGoodbyeHellContainer; // the control to be drawn<br /> CWsScreenDevice* wsScreenDevice = iCoeEnv->ScreenDevice();<br /> CFbsBitmap* bitmap = new(ELeave) CFbsBitmap; // the bitmap on which the control to be drawn<br /> CleanupStack::PushL(bitmap);<br /> TInt err = bitmap->Create(control->Size(), wsScreenDevice->DisplayMode());<br /> User::LeaveIfError(err);<br /> CFbsBitmapDevice* bitDevice = CFbsBitmapDevice::NewL(bitmap);<br /> CleanupStack::PushL(bitDevice);<br /> CFbsBitGc* bitGc = NULL;<br /> err = bitDevice->CreateContext(bitGc);<br /> User::LeaveIfError(err);<br /> CleanupStack::PushL(bitGc);<br /> CWindowToBitmapMappingGc* w2bGc = CWindowToBitmapMappingGc::NewL(*wsScreenDevice, *bitGc);<br /> CleanupStack::PushL(w2bGc);<br /> control->SetCustomGc(w2bGc); // set GC to the one we created<br /> control->DrawNow(); // then draw the control (now on the bitmap we created)<br /> control->SetCustomGc(NULL); // reset the GC </p> <p> // in this example we'd like to save the bitmap to a .bmp file<br /> // so that we can easily check it out<br /> _LIT(KFileName, "c://data//control.bmp");<br /> _LIT8(KMIME, "image/bmp");<br /> CImageEncoder* encoder = CImageEncoder::FileNewL(fs, KFileName, KMIME, CImageEncoder::EOptionAlwaysThread);<br /> CleanupStack::PushL(encoder);<br /> TRequestStatus status = KRequestPending;<br /> encoder->Convert(&status, *bitmap);<br /> User::WaitForRequest(status);<br /> User::LeaveIfError(status.Int());<br /> CleanupStack::PopAndDestroy(encoder);</p> <p> CleanupStack::PopAndDestroy(w2bGc);<br /> CleanupStack::PopAndDestroy(bitGc);<br /> CleanupStack::PopAndDestroy(bitDevice);<br /> CleanupStack::PopAndDestroy(bitmap);<br /> // end by chen<br /> return ETrue;<br /> }<br /> ...<br />

原文地址http://wiki.forum.nokia.com/index.php/How_to_draw_controls_on_bitmap