public extern static Int32 GetThemeBackgroundRegion(IntPtr hTheme, IntPtr hdc, int iPartId, int iStateId, ref RECT pRect, out IntPtr pRegion);

Declare Function GetThemeBackgroundRegion Lib "uxtheme.dll" (TODO) As TODO

Public Shared Function GetThemeBackgroundRegion(hTheme As IntPtr, hdc As IntPtr, iPartId As Integer, iStateId As Integer, ByRef pRect As RECT, ByRef pRegion As IntPtr) As Int32