addiconhandle needs to know if the icon is alpha

I got an application needs to list the most recent open files in the popup button in commandbars.

 

I got no problem to get the icon handle with SHGetFileInfo API.

 

but when I try to use addIconHandle to add the icon to the commandbars, there is a problem when setting the "Alpha" parameter.

 

when I use    mainCommandbars.AddIconHandle fileIconHandle, fileIconHandle, xtpImageNormal, True

 

when I use    mainCommandbars.AddIconHandle fileIconHandle, fileIconHandle, xtpImageNormal, false

 

it seems when icon has no alpha channel, the parameter has to be set to false , otherwise it wouldn't show. But when set parameter to false, some icons with alpha channel would show a black around itself instead of shadow.

 

is there  a way to tell from icon handle if the icon has alpha channel?

 

 

thank you very much!!!