LOCAL oForm
oForm = CREATEOBJECT("Tform")
oForm.Show(1)
* end of main
 
DEFINE CLASS Tform As Form
    Width=350
    Height=160
    BorderStyle=2
    MaxButton=.F.
    MinButton=.F.
    Autocenter=.T.
    Caption="Magnifier"
    hForm=0
    hDC=0
 
    ADD OBJECT chMagnify As CheckBox WITH Value=.F.,;
    Left=20, Top=20, Autosize=.T., Caption="Activate Magnifier"
 
    ADD OBJECT chInvert As CheckBox WITH Value=.F.,;
    Left=20, Top=56, Autosize=.T., Caption="Invert colors"
 
    ADD OBJECT lbl1 As Label WITH;
    Left=190, Top=20, Autosize=.T., Caption="Scale:"
 
    ADD OBJECT cmbScale As ComboBox WITH Style=2,;
    Left=240, Top=20, Width=70, Height=21
 
    ADD OBJECT cmdClose As CommandButton WITH Cancel=.T.,;
    Left=140, Top=112, Width=70, Height=27, Caption="Close"
 
PROCEDURE Init
    THIS.declare
 
PROCEDURE Activate
    IF THIS.hForm = 0
        THIS.hForm = GetFocus()
        THIS.hDC = GetDC(THIS.hForm)
    ENDIF
 
PROCEDURE Destroy
    IF THIS.hDC <> 0
        = ReleaseDC(THIS.hForm, THIS.hDC)
    ENDIF
 
PROCEDURE cmdClose.Click
    ThisForm.Release
 
PROCEDURE cmbScale.Init
    WITH THIS
        .AddItem("Normal")
        .AddItem("x 2")
        .AddItem("x 3")
        .AddItem("x 4")
        .ListIndex=3
    ENDWITH
 
PROCEDURE MouseMove
LPARAMETERS nButton, nShift, nXCoord, nYCoord
    THIS.Magnify
 
PROCEDURE chMagnify.MouseMove
LPARAMETERS nButton, nShift, nXCoord, nYCoord
    ThisForm.Magnify
 
PROCEDURE chInvert.MouseMove
LPARAMETERS nButton, nShift, nXCoord, nYCoord
    ThisForm.Magnify
 
PROCEDURE lbl1.MouseMove
LPARAMETERS nButton, nShift, nXCoord, nYCoord
    ThisForm.Magnify
 
PROCEDURE cmbScale.MouseMove
LPARAMETERS nButton, nShift, nXCoord, nYCoord
    ThisForm.Magnify
 
PROCEDURE cmdClose.MouseMove
LPARAMETERS nButton, nShift, nXCoord, nYCoord
    ThisForm.Magnify
 
PROCEDURE Magnify
#DEFINE SRCCOPY 0xCC0020
#DEFINE NOTSRCCOPY 0x00330008
#DEFINE cnDstWidth 600
#DEFINE cnDstHeight 140
 
    IF THIS.chMagnify.Value
        LOCAL cBuffer, nX, nY, hDstWin, hDstDC,;
            nMode, nSrcWidth, nSrcHeight, nScale
 
        hDstWin = GetActiveWindow()
        hDstDC = GetWindowDC(hDstWin)
 
        cBuffer = REPLICATE(Chr(0), 8)
        = GetCursorPos(@cBuffer)
        = ScreenToClient(THIS.hForm, @cBuffer)
 
        nX = buf2dword(SUBSTR(cBuffer, 1,4))
        nY = buf2dword(SUBSTR(cBuffer, 5,4))
 
        nScale = THIS.cmbScale.ListIndex
        nSrcWidth = INT(cnDstWidth/nScale)
        nSrcHeight = INT(cnDstHeight/nScale)
 
        nMode = IIF(THIS.chInvert.Value,;
            NOTSRCCOPY, SRCCOPY)
 
        = StretchBlt(hDstDC, 10, 100,;
            cnDstWidth, cnDstHeight, THIS.hDC,;
            nX-nSrcWidth/2, nY-nSrcHeight/2,;
            nSrcWidth, nSrcHeight, nMode)
 
        = ReleaseDC(hDstWin, hDstDC)
    ENDIF
 
PROCEDURE declare
    DECLARE INTEGER GetActiveWindow IN user32
    DECLARE INTEGER GetCursorPos IN user32 STRING @lpPoint
    DECLARE INTEGER GetWindowDC IN user32 INTEGER hwnd
    DECLARE INTEGER GetDC IN user32 INTEGER hwnd
    DECLARE INTEGER GetFocus IN user32
 
    DECLARE INTEGER ReleaseDC IN user32;
        INTEGER hWindow, INTEGER hdc
 
    DECLARE INTEGER ScreenToClient IN user32;
        INTEGER hWindow, STRING @lpPoint
 
    DECLARE INTEGER StretchBlt IN gdi32;
        INTEGER hdcDest, INTEGER nXOriginDest,;
        INTEGER nYOriginDest, INTEGER nWidthDest,;
        INTEGER nHeightDest, INTEGER hdcSrc,;
        INTEGER nXOriginSrc, INTEGER nYOriginSrc,;
        INTEGER nWidthSrc, INTEGER nHeightSrc,;
        INTEGER dwRop
 
ENDDEFINE
 
FUNCTION buf2dword(lcBuffer)
RETURN Asc(SUBSTR(lcBuffer, 1,1)) + ;
    BitLShift(Asc(SUBSTR(lcBuffer, 2,1)), 8) +;
    BitLShift(Asc(SUBSTR(lcBuffer, 3,1)), 16) +;
    BitLShift(Asc(SUBSTR(lcBuffer, 4,1)), 24)