_WinAPI_GetDC related

[JohnOne]

I'm not so sure about what exactly hdc is.

My question and code example might help to ask my question.

#include <WinAPI.au3>

$_GetPixel = _GetPixel(10, 10)

ConsoleWrite($_GetPixel &@LF)

Func _GetPixel($iX, $iY)
    $hDC = _WinAPI_GetDC(0)

    $aGetPixel = DllCall("Gdi32.dll", "dword", "GetPixel", "handle", $hDC, "int", $iX, "int", $iY)
    If @error Then
        Exit MsgBox(0, "DllCall Error", @error)
    EndIf

    $rtn = StringRight(Hex($aGetPixel[0]), 6)

    Return $rtn
EndFunc   ;==>_GetPixel

Code returns pixel color at screen coords.

Should I make the call to _WinAPI_GetDC each time my function is called or is it safe to have it called once globally, given that screen content can obviously change?

I'm not after a debate on the pro's and con's of global variables, and could just as well be static. Just whether the device context remains the same throughout the life of the script

I have tested this but I want to be sure.

[KaFu]

Afaik the DC stays the same as long as the hWnd stays the same, so as long as the desktop hwnd does not change, _WinAPI_GetDC(0) should stay the same and can be obtained one time globally. To free resources _WinAPI_ReleaseDC(0, $hDC) should also be called after usage, and btw., just saw in the MSDN doc comments that this will only get you the DC of the default monitor screen in a multi-monitor set-up, see said docs for a trick to get DC for whole screen in a multi-monitor set-up.

[JohnOne]

Thanks for the clarification KaFu.

Do you know what the relationship between desktop dc and desktop hwnd is?

For example If I try to perform a control* function on hwnd, it operates only on the desktop window.

If I perform GetPixel using the DC, I get the colour of anything visible on the whole screen regardless of what the window might be.

[KaFu]

About Device Contexts, something I still have to read too ...

[JohnOne]

Thank you very kindly KaFu.