Creating Alpha Mask Using Difference Between Two Images

[user2037]

In order to cope with custom-pointer images I'm trying to create an alpha mask by sampling a screen region with and without the pointer. Creating the mask of the unchanged pixels is not obvious to me. (Being new to GDI.)

Any ideas?

[eukalyptus]

You can blit one image on the other using the XOR operator:

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#include <WinAPI.au3>
#include <WindowsConstants.au3>
#include <GDIPlus.au3>


Global $hGui = GUICreate("", 604, 202)
GUISetBkColor(0x0000FF)
Global $hDC = _WinAPI_GetDC($hGui)
Global $hCDC = _WinAPI_CreateCompatibleDC($hDC)
GUISetState()

Global $hBMP_1, $hBMP_2
_CreateGraphics($hBMP_1, $hBMP_2)

Local $hOBJ = _WinAPI_SelectObject($hCDC, $hBMP_1)
_WinAPI_BitBlt($hDC, 1, 1, 200, 200, $hCDC, 0, 0, $SRCCOPY)
_WinAPI_SelectObject($hCDC, $hBMP_2)
_WinAPI_BitBlt($hDC, 202, 1, 200, 200, $hCDC, 0, 0, $SRCCOPY)


Global $iMode = 0
Global $iTimer = TimerInit()
While GUIGetMsg() <> -3
    If TimerDiff($iTimer) > 500 Then
        $iTimer = TimerInit()
        Switch $iMode
            Case 1
                _WinAPI_SelectObject($hCDC, $hBMP_2)
                _WinAPI_BitBlt($hDC, 403, 1, 200, 200, $hCDC, 0, 0, $SRCCOPY)
                $iMode = 2
            Case 2
                _WinAPI_SelectObject($hCDC, $hBMP_1)
                _WinAPI_BitBlt($hDC, 403, 1, 200, 200, $hCDC, 0, 0, $SRCCOPY)
                _WinAPI_SelectObject($hCDC, $hBMP_2)
                _WinAPI_BitBlt($hDC, 403, 1, 200, 200, $hCDC, 0, 0, $SRCINVERT) ;<---- XOR
                $iMode = 0
            Case Else
                _WinAPI_SelectObject($hCDC, $hBMP_1)
                _WinAPI_BitBlt($hDC, 403, 1, 200, 200, $hCDC, 0, 0, $SRCCOPY)
                $iMode = 1
        EndSwitch
    EndIf
WEnd

_WinAPI_SelectObject($hCDC, $hOBJ)
_WinAPI_DeleteObject($hBMP_1)
_WinAPI_DeleteObject($hBMP_2)
_WinAPI_DeleteDC($hCDC)
_WinAPI_ReleaseDC($hGui, $hDC)









Func _CreateGraphics(ByRef $hBMP_1, ByRef $hBMP_2)
    _GDIPlus_Startup()

    Local $hBitmap = _GDIPlus_BitmapCreateFromScan0(200, 200)
    Local $hContext = _GDIPlus_ImageGetGraphicsContext($hBitmap)
    _GDIPlus_GraphicsSetSmoothingMode($hContext, 2)
    _GDIPlus_GraphicsClear($hContext, 0xFFFFFFFF)
    Local $hPen = _GDIPlus_PenCreate(0xFF00FF00, 5)


    For $i = 1 To 10
        _GDIPlus_PenSetColor($hPen, BitOR(0xFF000000, BitShift(Random(0, 255, 1), -16), BitShift(Random(0, 255, 1), -8), Random(0, 255, 1)))
        _GDIPlus_GraphicsDrawLine($hContext, Random(0, 200), Random(0, 200), Random(0, 200), Random(0, 200), $hPen)
    Next
    $hBMP_1 = _GDIPlus_BitmapCreateHBITMAPFromBitmap($hBitmap)

    For $i = 1 To 4
        _GDIPlus_PenSetColor($hPen, BitOR(0xFF000000, BitShift(Random(0, 255, 1), -16), BitShift(Random(0, 255, 1), -8), Random(0, 255, 1)))
        _GDIPlus_GraphicsDrawLine($hContext, Random(0, 200), Random(0, 200), Random(0, 200), Random(0, 200), $hPen)
    Next
    $hBMP_2 = _GDIPlus_BitmapCreateHBITMAPFromBitmap($hBitmap)


    _GDIPlus_PenDispose($hPen)
    _GDIPlus_GraphicsDispose($hContext)
    _GDIPlus_BitmapDispose($hBitmap)
    _GDIPlus_Shutdown()
EndFunc   ;==>_CreateGraphics