Option Explicit

Public Sub BresLine(ByVal x1 As Long, ByVal y1 As Long, ByVal x2 _
      As Long, ByVal y2 As Long, ByVal Color As Long)

  Dim LWidth    As Long
  Dim LHeight   As Long
  Dim d         As Long
  Dim ix        As Long
  Dim iy        As Long
  Dim dd        As Integer
  Dim id        As Integer
  Dim EmptyRect As RECT
  Dim SurfDesc  As DDSURFACEDESC2

  BackBuffer.Lock EmptyRect, SurfDesc, DDLOCK_WRITEONLY, 0

  LWidth = x2 - x1
  LHeight = y2 - y1
  d = 0

  If LWidth < 0 Then
    LWidth = -LWidth
    ix = -1
  Else
    ix = 1
  End If

  If LHeight < 0 Then
    LHeight = -LHeight
    iy = -1
  Else
    iy = 1
  End If

  If LWidth > LHeight Then
    dd = LWidth + LWidth
    id = LHeight + LHeight

    Do
      BackBuffer.SetLockedPixel x1, y1, Color
      If x1 = x2 Then Exit Do
      x1 = x1 + ix
      d = d + id

      If d > LWidth Then
        y1 = y1 + iy
        d = d - dd
      End If
    Loop

  Else
    dd = LHeight + LHeight
    id = LWidth + LWidth

    Do
      BackBuffer.SetLockedPixel x1, y1, Color
      If y1 = y2 Then Exit Do
      y1 = y1 + iy
      d = d + id

      If d > LHeight Then
        x1 = x1 + ix
        d = d - dd
      End If
    Loop
  End If

  BackBuffer.Unlock EmptyRect
End Sub