Make mouse pointer in the center of the dialog

[Davider]

My English is not good,
In the following code, I added a mouse mid button trigger

When I press the middle mouse button: 

I need the dialog window to be fully displayed, The central position of the dialog window is always in the center of the mouse pointer

But, When the middle mouse button is pressed at the edge of the screen, it needs to be processed, and the mouse pointer is located in the center of the dialog box 

Macro Macro2
Trigger #M     

Code:

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str dd=
;BEGIN DIALOG
;0 "" 0x90C802C8 0x0 0 0 224 136 "Dialog"
;1 Button 0x54030001 0x4 116 116 48 14 "OK"
;2 Button 0x54030000 0x4 168 116 48 14 "Cancel"
;END DIALOG
;DIALOG EDITOR: "" 0x2040800 "*" "" "" ""

if(!ShowDialog(dd &sub.DlgProc 0)) ret

#sub DlgProc
function# hDlg message wParam lParam

sel message
,case WM_INITDIALOG
,POINT p; xm(p) ;;get mouse position into p.x and p.y
,mov p.x p.y hDlg
,case WM_DESTROY
,case WM_COMMAND goto messages2
ret
;messages2
sel wParam
,case IDOK
,case IDCANCEL
ret 1