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'System & API - How to Limit Cursor Movement to Form Boundaries

Option Explicit
 
Public Type RECT
    left As Integer
    top As Integer
    right As Integer
    bottom As Integer
End Type
Public Type POINT
    x As Long
    y As Long
End Type
Declare Sub ClipCursor Lib "user32" (lpRect As Any)
Declare Sub GetClientRect Lib "user32" (ByVal hWnd As Long, lpRect As RECT)
Declare Sub ClientToScreen Lib "user32" (ByVal hWnd As Long, lpPoint As POINT)
Declare Sub OffsetRect Lib "user32" (lpRect As RECT, ByVal x As Long, ByVal y As Long)
 
'Add two Command Buttons to your form and set its caption as "Limit Cursor Movement", "Release Limit"

Private Sub Command1_Click()
    Dim client As RECT
    Dim upperleft As POINT
    GetClientRect Me.hWnd, client
    upperleft.x = client.left
    upperleft.y = client.top
    ClientToScreen Me.hWnd, upperleft
    OffsetRect client, upperleft.x, upperleft.y
    ClipCursor client
End Sub
 
Private Sub Command2_Click()
    ClipCursor ByVal 0&
End Sub
 
Private Sub Form_Unload(Cancel As Integer)
    'If you won't put the code line below in the form's unload event, the cursor will
    'be still limited to the last coordinates after the program unloaded.
    ClipCursor ByVal 0&
End Sub