Window State

The WND structure has from the start provided a set of bit fields in union with the state member as a ULONG. Microsoft’s names and definitions are known from symbol files for WIN32K.SYS from Windows 7 only.

The USEREXTS and USERKDX debugger extensions, as supplied in the Device Driver Kit (DDK) for Windows NT 3.51 through to Windows 2000 but apparently not since, have names that likely reproduce macros from Microsoft’s headers. These name a sort of index into the set of window flags that comprises the state, state2, ExStyle and style members considered as an array of bytes. The high byte in each such 16-bit index is the byte offset to the bit and the low byte is the bit mask within that byte.

All but half a dozen of these 32 bit fields are well-defined through the whole history of Windows—and those few changes are from as long ago as Windows 2000.

INT bHasMeun : 1;

INT bHasVerticalScrollbar : 1;

INT bHasHorizontalScrollbar : 1;

INT bHasCaption : 1;

INT bSendSizeMoveMsgs : 1;

INT bMsgBox : 1;

INT bActiveFrame : 1;

INT bHasSPB : 1;

INT bNoNCPaint : 1;

INT bSendEraseBackground : 1;

INT bEraseBackground : 1;

INT bSendNCPaint : 1;

INT bInternalPaint : 1;

INT bUpdateDirty : 1;

INT bHiddenPopup : 1;

INT bForceMenuDraw : 1;

INT bDialogWindow : 1;

INT bHasCreatestructName : 1;

INT bServerSideWindowProc : 1;

INT bAnsiWindowProc : 1;

INT bBeingActivated : 1;

INT bHasPalette : 1;

INT bPaintNotProcessed : 1;

INT bSyncPaintPending : 1;

INT bRecievedQuerySuspendMsg : 1;

INT bRecievedSuspendMsg : 1;

INT bToggleTopmost : 1;

INT bRedrawIfHung : 1;

INT bRedrawFrameIfHung : 1;

INT bAnsiCreator : 1;

INT bMaximizesToMonitor : 1;

INT bDestroyed : 1;

The mis-spellings bHasMeun, bRecievedQuerySuspendMsg and bRecievedSuspendMsg are Microsoft’s.

The first four flags, along with the later addition bHasClientEdge in state2, are recalculated whenever the window’s client rectangle is recalculated.

The bSendSizeMoveMsgs flag is set when a window is created but has neither the WS_CHILD nor WS_POPUP styles. Such a window is not sent WM_SIZE and WM_MOVE messages while being created. These messages are instead deferred until the first ShowWindow (which clears the flag).

Debugger extensions for both Windows NT 3.51 and 4.0 have WFNOPAINT for the 16-bit encoding that corresponds to the state mask 0x00000020. I know of no reason to disbelieve this name but neither do I know of any use of this bit field before version 5.0 evidently repurposed it. The same applies also to the 0x00100000 and 0x40000000 flags, whose encodings the debugger extensions name as WF16BIT and WFPALETTEWINDOW in the early versions.

Debugger extensions for both Windows NT 4.0 and Windows 2000 define WFANYHUNGREDRAW for the combination of closely related bit fields bRedrawIfHung and bRedrawFrameIfHung. Presumably, it is used—but if so, the only known use has the constant optimised away when testing whether either bit is set. If that is the only use, then it dates from version 3.51, no matter that the debugger extension for Windows NT 3.51 omits it.