Would it be possible to document how the common controls are drawn? (parts, states, borders, margins etc.)  I'm trying to custom draw a header control so I can have multiple lines of text in each item but retain the standard appearance. It's great that functions are provided for retrieving the sizes of the various parts (GetThemeMetrics(), GetThemeMargins(), GetThemeInt() etc.) but they're not that useful if you don't know what sizes to request. The main problem I have is that I don't know how to determine the size of the button when using the HDF_SPLITBUTTON header item flag. Any information you can provide will be gratefully received.

DOH!

 I got so focused on the visual styles API's that I completely overlooked the Header_GetItemDropDownRect function.