Moving the end of a line using mouse scroll wheel

[c.haslam]

Here is my code:

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#include <GUIConstantsEx.au3>
#include <StaticConstants.au3>
#include <WindowsConstants.au3>

GUIRegisterMsg($WM_MOUSEWHEEL, "WM_MOUSEWHEEL")

Local $Form1 = GUICreate("Form1", 623, 449, 192, 114)
GUISetState(@SW_SHOW)

Global $n = 39,$nMsg,$oldn=-1,$Graphic1=0
While 1
    If $n<>$oldn Then
        If $Graphic1<>0 Then
            GUICtrlDelete($Graphic1)
        EndIf
        $Graphic1 = GUICtrlCreateGraphic(0, 0, 605, 441)
        GUICtrlSetGraphic($Graphic1, $GUI_GR_MOVE, 9, 39)
        GUICtrlSetGraphic($Graphic1, $GUI_GR_LINE, 300, $n)
        $oldn = $n
    Else
        $nMsg = GUIGetMsg()
        Switch $nMsg
            Case $GUI_EVENT_CLOSE
                Exit
        EndSwitch
    EndIf
WEnd

Func WM_MOUSEWHEEL($hWnd,$iMsg, $iwParam, $ilParam)
    #forceref $hwnd, $iMsg, $ilParam
    Local $a = GUIGetCursorInfo($Form1)
    If $a[4] = $Graphic1 Then
        Local $iDelta = BitShift($iwParam, 16)
        If $iDelta > 0 Then $n += 5
        If $iDelta < 0 Then $n -= 5
    EndIf
  Return $GUI_RUNDEFMSG
EndFunc

When the wheel is "wheeled", the right end of the line should move up or down. It doesn't.

In fact, the line does not appear at all.

With the cursor inside the control, inserting MsgBox(0,'','here') after $oldn = $n shows me that the If .. Else code is executed.

Suggestions?

[c.haslam]

I am answering my own question.  It seems that the native functions are unable to handle the problem. I turned to GDI+, so here is a simple example of GDI+ graphics, thanks to Mat (Post 6)

I also thank all those others whose posts led me in a direction that works.

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#include <GDIPlus.au3>
#include <GUIConstantsEx.au3>
#include <WindowsConstants.au3>
Opt('MustDeclareVars',1)

Global Const $MK_SHIFT = 0x4
Global Const $MK_CONTROL = 0x8

GUIRegisterMsg($WM_MOUSEWHEEL, "WM_MOUSEWHEEL")

Global $gY0,$gY1,$ghGui,$gLabel

Example()

Func Example()
    Local $ghGui, $hGraphic, $hPen
    Local $oldY0,$oldY1

    ; Create GUI
    $ghGui = GUICreate("GDI+", 400, 330)
    $gLabel = GUICtrlCreateLabel('',0,0,400,250)
    GUICtrlCreateLabel('Scroll mouse to move whole line',10,251,300,17)
    GUICtrlCreateLabel('Control scroll to move left end',10,271,300,17)
    GUICtrlCreateLabel('Shift scroll to move right end',10,291,300,17)
    Local $btn = GUICtrlCreateButton('Exit',351,291,30,20)
    GUISetState(@SW_SHOW)
    _GDIPlus_Startup()
    Local $h = GUICtrlGetHandle($gLabel)    ; limit graphics to area of $label
    $hGraphic = _GDIPlus_GraphicsCreateFromHWND($h)
    $hPen = _GDIPlus_PenCreate()
    _GDIPlus_GraphicsDrawLine($hGraphic, 10, $gY0, 350, $gY1, $hPen)

    $gY0 = 150
    $gY1 = 150
    ; Loop until the user exits.
    While True
        If $gY0<>$oldY0 Or $gY1<>$oldY1 Then
            _GDIPlus_GraphicsClear($hGraphic,0xFFD4D0C8)
            _GDIPlus_GraphicsDrawLine($hGraphic, 10, $gY0, 390, $gY1, $hPen)
            $oldY0 = $gY0
            $oldY1 = $gY1
        Else
            Switch GUIGetMsg()
                Case $GUI_EVENT_CLOSE,$btn
                    Exit
            EndSwitch
        EndIf
    WEnd

    ; Clean up resources
    _GDIPlus_PenDispose($hPen)
    _GDIPlus_GraphicsDispose($hGraphic)
    _GDIPlus_Shutdown()
EndFunc

Func WM_MOUSEWHEEL($hWnd, $iMsg, $wParam, $lParam)
    #forceref $hWnd, $iMsg, $wParam, $lParam

    Local $vec = GUIGetCursorInfo($ghGui)
    If $vec[4] = $gLabel Then
        Local $iDelta = BitShift($wParam, 16)   ; positive = up
        Local $iKeys = _WinAPI_LoWord($wParam)
        If BitAND($iKeys,$MK_CONTROL)=$MK_CONTROL Then
            If BitAND($iKeys,$MK_SHIFT)=$MK_SHIFT Then
                ; do nothing
            Else
                If $iDelta > 0 And $gY0>3 Then $gY0 -= 1
                If $iDelta < 0 And $gY0<247 Then $gY0 += 1
            EndIf
        Else
            If BitAND($iKeys,$MK_SHIFT)=$MK_SHIFT Then
                If $iDelta > 0 And $gY1>3 Then $gY1 -= 1
                If $iDelta < 0  And $gY1<247 Then $gY1 += 1
            Else
                If $iDelta > 0 And $gY0>3 Then $gY0 -= 1
                If $iDelta < 0 And $gY0<247 Then $gY0 += 1
                If $iDelta > 0 And $gY1>3 Then $gY1 -= 1
                If $iDelta < 0 And $gY1<247 Then $gY1 += 1
            EndIf
        EndIf
    EndIf
    Return $GUI_RUNDEFMSG
EndFunc   ;==>WM_MOUSEWHEEL

The script provides the user with the ability to move the whole line, and its left end, as well as the right end. My application does not require the line to be moved horizontally.

It appears that GDI+ can empty a graphic of all lines, etc. but not just one.

Comments and suggestions are most welcome.

Edited October 8, 2017 by c.haslam