WM_PAINT

[TpOreilly]

Hi, see:

HDC handleDeviceContext; 
    PAINTSTRUCT PaintSt;
	RECT aRect;

	switch(msg)
    {

		case WM_PAINT:

			handleDeviceContext = BeginPaint(hwnd, &PaintSt);
			
			GetClientRect(hwnd, &aRect);
			
			SetBkMode(handleDeviceContext, TRANSPARENT); 
			
			DrawText(handleDeviceContext, TEXT("It's a blizzard!"), -1, &aRect, DT_SINGLELINE|DT_CENTER| DT_VCENTER); 

			DrawText(handleDeviceContext, TEXT("It's a blizzard!!"), -1, &aRect, DT_SINGLELINE|DT_LEFT| DT_VCENTER); 
			
			EndPaint(hwnd, &PaintSt); 

			break;

Obviously "HDC handleDeviceContext;" makes a variable of the HDC type, What exactly am i passing to the handleDevliceContext variable by passing the return value of the BeginPaint() function?

Thanks.

[guestgulkan]

http://msdn.microsoft.com/en-us/library/dd183362(VS.85).aspx

[z05DSL3A]

TpOreilly wrote:

What exactly am i passing to the handleDevliceContext variable by passing the return value of the BeginPaint() function?

I am assuming you are asking 'what is stored in the variable handleDevliceContext?'
If you look at the typedef for a HGDIOBJ^* you would be forgiven for thinking that it is a pointer, it is not. Basically a Handle is an encoded number, in the case of a Handle to a GDI Object encoded in the number would be a bit to say if this a stock object, 7 bits to say what type of object it is (pen, brush, etc.) and a say 12 bits for an index for the object itself.


* HGDIOBJ is the most generic GDI object type.

[TpOreilly]

When i put "HDC handleDeviceContext;" im creating a handle with a name of handleDeviceContext arnt i?

And when i put handleDeviceContext = BeginPaint(hwnd, &PaintSt); I am giving handleDeviceContext the return value of BeginPaint() arnt it?

So i'm asking what is beginpaint() actually passing to to handleDeviceContext, so what is actually stored in the handleDeviceContext variable?

Thanks

[TpOreilly]

When i put "HDC handleDeviceContext;" im creating a handle variable and with name of handleDeviceContext arnt i.

When i put "handleDeviceContext = BeginPaint(hwnd, &PaintSt);" im assigning the return value of beginpaint() to the handleDeviceContext variable arnt i.

So im asking what is actually stored in the handleDeviceContext handle variable. Is the function creating a DC and then giving the variable handleDeviceContext the handle to this DC?

[z05DSL3A]

When i put "HDC handleDeviceContext;" im creating a handle variable and with name of handleDeviceContext arnt i.

Your are creating a variable named handleDeviceContext that is of type handle to a Device Context. This variable can store the HDC that is returned from BeginPaint().

So im asking what is actually stored in the handleDeviceContext handle variable. Is the function creating a DC and then giving the variable handleDeviceContext the handle to this DC?

Yes, BeginPaint() creates a DC that is stored away inside windows and returns a HDC so that you can refer to that DC with other functions. You assign it to the variable so that you don't loose it.

[TpOreilly]

Thanks

[TpOreilly]

I understand that the BeginPaint() function creates and provides a handle to a DC, but this function also "prepares the specified window for painting", im just wondering, what preparations does it do?

Cheers

[TpOreilly]

?

[guestgulkan]

The BeginPaint is an internal Windows OS function - I would imagine only certain privileged
people (microsoft programmers, and maybe some authors especially close to Microsoft) would
know the exact details.

Other non-priviledged programmers like you and I will get a Display Context handle and a PAINTSTRUCT variable with some data about the painting requirements.

[TpOreilly]

Fair enough :)