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Konstantine Voytenko's Forum Nokia Blog
Bitmap manipulation: Image buffer
Carbider | 13 June, 2008 10:16
The primary and secondary buffers may then be switched.
This is important because if to draw different picture elements to the main buffer (which continuously is mapped onto the screen of phone), user will watch flicker image. The same would be if try erasing the main buffer and then draw new frame of animation on it.
Use of the second bitmap can be attributed to the technology of "Dual buffering".
Let's look how can we realize this technique in a Symbian GUI project.
First, I'll abstract from the whole application and will show the core of creating and manipulating the buffer.
Secondary we will tie this to a simple 'Hello World!' GUI project which is available in Carbide.c++ IDE.
=== The Core ===
Let us create a Symbian C++ class that will have necessary properties and methods to organize the buffer. And also to draw to the buffer. That would be the RBitmapBuffer class.
{
public:
// Some constructors and cleanup stack operations omitted for clarity
The properties would be:
CFbsBitmap* iBitmapBuffer ; // Contains the bitmap whis is our buffer
CFbsBitGc * iDrawer ; // CFbsBitGc - the class to draw on Bitmap device
CFbsBitmapDevice* iBmpDevice ; // BitmapDevice is a mediator between the drawer and the buffer.
TRect iSizeOfScreenRect; // The size of the screen
TDisplayMode* pDisplayMode ; // The display mode of the buffer. In general this represents the color mode.
=============
The methods would be:
/* Two-phased constructor. */
RBitmapBuffer* RBitmapBuffer::NewL(const TDisplayMode&, const TRect& )
{
//omitted for clarity
//call to ConstructL
}
/* Initialize renderer */
void RBitmapBuffer::ConstructL(const TDisplayMode& aDisplayMode, const TRect& aSizeOfScreenRect)
{
setSizeOfScreen(aSizeOfScreenRect);
setDisplayMode (aDisplayMode);
iBitmapBuffer = new (ELeave) CFbsBitmap;
iBitmapBuffer ->Create(iSizeOfScreenRect.Size() , *pDisplayMode);
iDrawer = CFbsBitGc::NewL();
iBmpDevice = CFbsBitmapDevice::NewL(iBitmapBuffer);
// Activate virtual bitmap device
iDrawer -> Activate(iBmpDevice);
iDrawer -> SetPenColor(KRgbBlack);
/*
See the description below
*/
} // function
void RBitmapBuffer::setDisplayMode(const TDisplayMode& aDisplayMode)
{ pDisplayMode = (TDisplayMode*) &aDisplayMode; }
/* Sets sizeOfScreeen property */
void RBitmapBuffer::setSizeOfScreen(const TRect& aSizeOfScreenRect)
{ iSizeOfScreenRect = aSizeOfScreenRect; }
/* Returns the buffer pointer so any other class can use it */
CFbsBitmap* RBitmapBuffer::getBitmapBuffer()
{ return iBitmapBuffer; }
CFbsBitmap* RBitmapBuffer::Close()
{
delete iBitmapBuffer ; // Contains the bitmap whis is our buffer
delete iDrawer ; // CFbsBitGc - the class to draw on Bitmap device
delete iBmpDevice ; // BitmapDevice is a mediator between the drawer and the buffer.
}
} // class
Let's look through the ConstructL() method which prepares the bitmap buffer.
1. Set screen size.
2. Set display mode.
3. Allocate the object of CFbsBitmap class.
4. Initialize it by Create() method as empty buffer.
5. Allocate the CFbsBitGc and CFbsBitmapDevice objects to allow drawing to the bitmap buffer.
6. Show the iDrawer the device that it can draw. The device is iBmpDevice which is initialized with iBitmapBuffer object (the actual buffer).
7. Set the color of of drawer.
Now we can inherit the RBitmapBuffer class to create a new CBufferRenderer class which will draw something to the buffer.
Let's see:
{
public:
=============
The methods (except the constructors):
void CBufferRenderer::drawRect(TRect *aRect)
{
// Use parent's drawer mechanism
iDrawer->DrawRect ( *aRect );
}
void CBufferRenderer::~CBufferRenderer()
{
Close();
}
} // class
After instantiating the CBufferRenderer class we can draw some rectangles on it (or lots of other picture elements and bitmaps) and then return the buffer to the main program that will substitute the old screen image with the new one. The code will look like below:
{
TDisplayMode displayMode = iEikEnv->WsSession().GetDefModeMaxNumColors( color, gray );
TRect screenSize (10, 10, 20, 20);
TRect myRectangle (10, 10, 20, 20);
CBufferRenderer* myBackBuffer;
myBackBuffer = CBufferRenderer::NewL(screenSize, displayMode);
CleanupStack :: PushL(myBackBuffer);
myBackBuffer -> drawRect(&myRectangle);
someMainProgramDrawer -> (myBackBuffer->getBitmapBuffer);
CleanupStack :: Pop(myBackBuffer);
delete myBackBuffer;
} // function
Today I've shown the idea of the main core of the bitmap buffer.
This example has some pseudo code (the main program is not defined).
At the next post I'll show how to tie the RBitmapBuffer with the real Symbian GUI application.
However here is a list of the headers and libraries you will need to include to the project to use the above graphics classes:
bitgdi.lib
ws32.lib
S60, Symbian C++ |
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Comments (5) | 
Trackbacks (1)
Comments
RGA framework
Carbider | 14/06/2008, 10:49
Hi Lucian,
Yes thanks, here is a link to open C plugin for S60 3rd:
http://www.forum.nokia.com/main/resources/tools_and_sdks/openc_cpp/features.html
The questions is: can the RGA be mixed up with S60 GUI applications?
Re: Bitmap manipulation: Image buffer
ltomuta | 14/06/2008, 15:17
I would say yes but I wonder if in an efficient way. I expect that those using Avkon would ignore RGA and vice-versa, that's why your back buffer implementation will find I'm sure a lot of interested readers/users.
Re: Bitmap manipulation: Image buffer
korsun14 | 21/02/2009, 21:17
privet Konstantin, horoshaya stat'ya, pomogla mne reazobrat'sya s dual buffering tech. Mi gotovim materials for codeidol.com na temu symbian, mozhno copy tvoi stat'i?
hello, the good post, it helped me to learn dual buffering tech, can we use this essay on our webstore codeidol.com??
Re: Bitmap manipulation: Image buffer
ltomuta | 13/06/2008, 19:28
For those interested in the topic but willing a more standard/Open C++ approach they should have a look at the recently published RGA framework, it also provides back buffer implementation.