Displaying Alpha (32bit) Icons with ImageLists

Version 6 of ComCtl32.DLL (shipped with Windows XP) supports icons with alpha channels. This article describes how you can use icons with alpha channels with the vbAccelerator Image Lists.

Using ImageLists to Draw Alpha-Channel Icons

Versions of ComCtl32.DLL prior to 6.0 don't support drawing icons with alpha channels. For this reason, you first need to link your application to ComCtl32.DLL version 6.0. There are two articles which describe how to link your application to ComCtl32.DLL:

• At Design- and Debug- Time
• For a Compiled Executable

Once you've successfully set this up, then you're ready to create an alpha-channel ImageList. If you're using the vbAccelerator Image List Control, then you need to use version 2.0 (released on 14 January 2003) or above in order to persist icons added in the property pages. This was because the previous versions only persisted the icon graphics to a maximum of 24-bit colour resolution, resulting in the alpha channel begin discarded. If you're using the ImageList class or the System Image List then alpha channels are supported.

Then creating an ImageList which supports alpha icons is easy. Just set the ColourDepth to 32-bit (ILC_COLOR32) either prior to adding any images in the control or prior to calling Create in the class.

In Case You Can't

If your system doesn't support ImageLists allowing icons with alpha channels, or doesn't support alpha then trying to draw icons with an alpha channel will look bad:

Icon Drawn correctly with an Alpha Channel

Icon Drawn without Alpha Channel - the Drop Shadow renders all black.

You therefore should check in your application if alpha-icons are supported, and if not, fall back to icons without an alpha channel. There are two reasons why the system may not support alpha channels:

• Using a Pre-Windows XP version of ComCtl32.DLL
• If the system colour depth is less than 32 bits per pixel.

You can check whether the system supports alpha icons with the following code:

General Functions

Private Declare Function CreateDCAsNull Lib "gdi32" Alias "CreateDCA" ( _
    ByVal lpDriverName As String, _
    lpDeviceName As Any, _
    lpOutput As Any, _
    lpInitData As Any) As Long
Private Declare Function DeleteDC Lib "gdi32" ( _
    ByVal hdc As Long) As Long
Private Declare Function GetDeviceCaps Lib "gdi32" ( _
    ByVal hdc As Long, ByVal nIndex As Long) As Long
Private Const BITSPIXEL = 12         '  Number of bits per pixel
Private Const PLANES = 14            '  Number of planes

Private Type DLLVERSIONINFO
    cbSize As Long
    dwMajor As Long
    dwMinor As Long
    dwBuildNumber As Long
    dwPlatformID As Long
End Type
Private Declare Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" _
    (ByVal lpLibFileName As String) As Long
Private Declare Function FreeLibrary Lib "kernel32" _
    (ByVal hLibModule As Long) As Long
Private Declare Function GetProcAddress Lib "kernel32" _
    (ByVal hModule As Long, ByVal lpProcName As String) As Long
Private Declare Function DllGetVersion Lib "comctl32" _
    (pdvi As DLLVERSIONINFO) As Long
Private Const S_OK = 0

Public Function BitsPerPixel() As Long
Dim lhDCD As Long
Dim lBitsPixel As Long
Dim lPlanes As Long
   lhDCD = CreateDCAsNull("DISPLAY", ByVal 0&, ByVal 0&, ByVal 0&)
   lBitsPixel = GetDeviceCaps(lhDCD, BITSPIXEL)
   lPlanes = GetDeviceCaps(lhDCD, PLANES)
   BitsPerPixel = (lBitsPixel * lPlanes)
   DeleteDC lhDCD
End Function

Public Function ComCtlVersion( _
        ByRef lMajor As Long, _
        ByRef lMinor As Long, _
        Optional ByRef lBuild As Long _
    ) As Boolean
Dim hMod As Long
Dim lR As Long
Dim lptrDLLVersion As Long
Dim tDVI As DLLVERSIONINFO

    lMajor = 0: lMinor = 0: lBuild = 0

    hMod = LoadLibrary("comctl32.dll")
    If Not(hMod = 0) Then
        lR = S_OK
        ' You must get this function explicitly because earlier versions 
        ' of the DLL don't implement this function. That makes the 
        ' lack of implementation of the function a version 
        ' marker in itself.
        lptrDLLVersion = GetProcAddress(hMod, "DllGetVersion")
        If Not(lptrDLLVersion = 0) Then
            tDVI.cbSize = Len(tDVI)
            lR = DllGetVersion(tDVI)
            If (lR = S_OK) Then
                lMajor = tDVI.dwMajor
                lMinor = tDVI.dwMinor
                lBuild = tDVI.dwBuildNumber
            End If
        Else
            'If GetProcAddress failed, then the DLL is a 
            ' version previous to the one shipped with IE 3.x.
            lMajor = 4
        End If
        FreeLibrary hMod
        ComCtlVersion = True
    End If

End Function

Checking Code

   Dim bSupportsAlphaIcons As Boolean
   If (BitsPerPixel >= 32) Then
      Dim lMajor As Long
      Dim lMinor As Long
      ComCtlVersion lMajor, lMinor
      If (lMajor >= 6) Then
         bSupportsAlphaIcons = True
      End If
   End If