[VB6] - about DC's

[Cambalinho]

i did 1 class for working with DC's(double buffering):

Option Explicit

Private Type DC
     handleDC As Long
     handleBMP As Long
     handleRefBMP As Long
End Type

Private Declare Function CreateCompatibleBitmap Lib "gdi32" (ByVal hdc As Long, ByVal nWidth As Long, ByVal nHeight As Long) As Long
Private Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) As Long
Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long
Private Declare Function DeleteDC Lib "gdi32" (ByVal hdc As Long) As Long
Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long

Dim SourceDC As DC
Dim lngWidth As Long
Dim lngHeight As Long

Public Sub GetImage(ByRef hdc As Long, ByRef Width As Long, ByRef Height As Long)
    SourceDC.handleDC = CreateCompatibleDC(hdc)
    SourceDC.handleBMP = CreateCompatibleBitmap(SourceDC.handleDC, Width, Height)
    SourceDC.handleRefBMP = SelectObject(SourceDC.handleDC, SourceDC.handleBMP)
    BitBlt SourceDC.handleDC, 0, 0, Width, Height, hdc, 0, 0, vbSrcCopy
    lngHeight = Height
    lngWidth = Width
End Sub

Public Sub DrawImage(ByRef hdc As Long)
    BitBlt hdc, 0, 0, lngWidth, lngHeight, SourceDC.handleDC, 0, 0, vbSrcCopy
End Sub

Private Sub Class_Terminate()
    DeleteObject SelectObject(SourceDC.handleDC, SourceDC.handleRefBMP)
    DeleteObject SourceDC.handleBMP
    DeleteDC SourceDC.handleDC
End Sub

why instead copy\draw the image, copy a mask image?