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Windows CE Basics

Windows CE is an operating system optimised for the embedded devices.It is a subset of its parent OS windows which runs on desktops.Not all the win32 API's are supprted by windows CE.But it has sufficient of them to carry out most basic of oprations.If you have previously worked on windows than working with windows CE is not that different.Only you need to take of some new functions and procedures.And you need to optimize your code so that it consumes less resources and executes in shorter time.

WHERE to START

Make sure you know about the basics of windows CE.Like

1.WinCE supports UNICODE programming model.

2.Study about the GDI of Windows CE.GDI is the part of GWES(Graphics Windowing and Event subsystem) which takes care of your all drawing needs from drawing a single line to AlphaBlendind an bitmap image.

3.you should know the basic flow of the program.When you build a non empty smartdevice project from your visual studio,it will generate a code which contains the basic skeleton of windows CE application.

a.Winmain is the starting point of the program

int WINAPI WinMain(HINSTANCE hInstance,

HINSTANCE hPrevInstance,

LPTSTR lpCmdLine,

int nCmdShow)

b.Before we create a window we need register its windows Class, which is done by myregisterclass

function.Here we can modify the styles of the window,background color etc.By default background color is White.If we use HOLLOW_BRUSH instead of WHITE_BRUSH than it will not paint our window.It will produce a transparent window.We have to take care about painting and erasing the window.

ATOM MyRegisterClass(HINSTANCE hInstance, LPTSTR szWindowClass)

{

WNDCLASS wc;

wc.style = CS_HREDRAW | CS_VREDRAW;

wc.lpfnWndProc = WndProc;

wc.cbClsExtra = 0;

wc.cbWndExtra = 0;

wc.hInstance = hInstance;

wc.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_NONAME));

wc.hCursor = 0;

wc.hbrBackground = (HBRUSH) GetStockObject(WHITE_BRUSH);

wc.lpszMenuName = 0;

wc.lpszClassName = szWindowClass;

return RegisterClass(&wc);

}

c.After u register you window class,it creates a window using CreateWindow API.This function returns a handle to that window which is termed as window handle(HWND).In this function we can give the initial position ,width and height of our window.

hWnd = CreateWindow(szWindowClass, szTitle, WS_VISIBLE,

CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL);

d.Than we encounter the Message Loop.This is the Main part of the Code.Here all the meesages sent by the os are dispatched and sent to Windows Procedure.

while (GetMessage(&msg, NULL, 0, 0))

{

if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))

{

TranslateMessage(&msg);

DispatchMessage(&msg);

}

}

f.As explained before windows procedure is the one which gets all the messages sent by the os.SO here we can see the switch statements are used to take custom actions to the messages sent by the OS.There are huge set of messages that u may receive from the OS.We need not to take care about all of them.The DefWndProc at the default case statement takes care about the unhandled windows messages

default:

return DefWindowProc(hWnd, message, wParam, lParam);

}

return 0;

Now you know the basic skeleton of the windows CE.Few more random important points for the beginners.

1.Make sure u delete all the HDC(handle to the Device Context) that u created using createcompatibleDC api.If u got HDC from GetDC api u should release the DC by calling releaseDC api.

2.If u r trying to load a image into your application either from resource or from remote path.Make sure that your image is 24bit bit wide .BMP file.Winodows CE doesnt support loadind 32bit wide bmp images.U can load images by either LoadImage() or ShloadBitmap() api's

3.AlphaBlend() function returns zero if the size of the source provided in the function mismatches with the original size of the source.What I mean to say is that you cannot partially alphablend the source.

4.In order to have flicker free controls in windows CE use Off-Screen DC.Do all your drawings onto to an off-screen DC.Than later transfer the contents from offscreen DC into the main DC usin BitBlt function.Create off-Screen DC using createcompatibleDC function and laod a compatible bitmap into it.Make sure you delete your Off-Screen DC after you use it.

5.Windows CE doesnt support alphablended windows.So we need to simulate the alhablending effect.This can be achieved by capturing the screen image using GetDC(NULL) and alpha blendind that with our windows HDC.GetDC(NULL) returns the HDC of the current ScreenMake sure you release the HDC which you got from GetDC function .

5.How to remove the window startup animation?

Use WS_EX_NOANIMATION flag in your createwindowEx function.This will remove the animation and it will also remove the applications reference from the task manager and taskbar.

6.How to get our window on top of full screen video?

Use WS_EX_TOPMOST flag in your createWindowEx function.

7.Child Window X,Y position is with respect to parent window X,Y positions not with screen's X,Y positions.