[vb6] Get the current color depth

If you are displaying graphics, you might like to learn the current color depth - true-color bitmaps generally don't look good on 256-color screens. The ColorDepth function returns the color depth as a bits per pixel number, for example on a true-color display the function will return 24. The function obtains a screen dc because the GetDeviceCaps function needs a dc for input.

    Private Const PLANES& = 14
    Private Const BITSPIXEL& = 12
    Private Declare Function GetDeviceCaps& Lib "gdi32" (ByVal hdc As Long, ByVal nIndex As Long)
    Private Declare Function GetDC& Lib "user32" (ByVal hwnd As Long)
    Private Declare Function ReleaseDC& Lib "user32" (ByVal hwnd As Long, ByVal hdc As Long)
    
    Private Function ColorDepth() As Integer
      Dim nPlanes As Integer, BitsPerPixel As Integer, dc As Long
      dc = GetDC(0)
      nPlanes = GetDeviceCaps(dc, PLANES)
      BitsPerPixel = GetDeviceCaps(dc, BITSPIXEL)
      ReleaseDC 0, dc
      ColorDepth = nPlanes * BitsPerPixel
    End Function