Why doesn't WTSConnectSession work when I first tried it?

Because the MSDN documentation on WTSConnectSession is wrong.

If you follow it:

Parameters

LogonId [in]

The logon ID of the current session, where the user of that session has permissions to connect to an existing session.

TargetLogonId [in]

The logon ID of the session that you want to connect to.

And call the function this way, your program will merely disconnect your current session with ERROR_NOT_CONNECTED, leaving you to wonder if the execution of the program stops in the middle of the call.

Once you find out that WTSConnectSession is just a wrapper for the undocumented WinStationConnect, which exists in earlier versions of Windows than its wrapper, you should realize that the first two parameters as documented are swapped.

RichTextBox is not a simple RichEdit wrapper?

There are several annoyances with the Rich Edit control. For example, using EM_STREAMIN / EM_STREAMOUT with EditStreamCallback will clear its undo and redo queues. Why would this caused by simply reading the stream is beyond me.

The .net RichTextBox inherits this problem, which means accessing its Text, Rtf, and Lines properties will clear the queues. What's more, calling its GetCharIndexFromPosition and GetPositionFromCharIndex functions will also clear the queues. Why is that? Don't GetCharIndexFromPosition and GetPositionFromCharIndex just wrap EM_CHARFROMPOS and EM_POSFROMCHAR?

Workarounds?

• Replace functions GetCharIndexFromPosition / GetPositionFromCharIndex with EM_CHARFROMPOS / EM_POSFROMCHAR
• Replace property Text with EM_GETTEXTEX / RichTextBox.SelectAll / SelectedText
• Replace property Lines with EM_GETTEXTEX / String.Split / Join
• Replace property Rtf with... no idea.

What's wrong with WS_EX_LAYERED and WS_EX_COMPOSITED?

From MSDN:

WS_EX_COMPOSITED

Windows XP: Paints all descendants of a window in bottom-to-top painting order using double-buffering. For more information, see Remarks. This cannot be used if the window has a class style of either CS_OWNDC or CS_CLASSDC.

WS_EX_LAYERED

Windows 2000/XP: Creates a layered window. Note that this cannot be used for child windows. Also, this cannot be used if the window has a class style of either CS_OWNDC or CS_CLASSDC.

Remarks

Windows XP: With WS_EX_COMPOSITED set, all descendants of a window get bottom-to-top painting order using double-buffering. Bottom-to-top painting order allows a descendent window to have translucency (alpha) and transparency (color-key) effects, but only if the descendent window also has the WS_EX_TRANSPARENT bit set. Double-buffering allows the window and its descendents to be painted without flicker.

If WS_EX_COMPOSITED is set on a dialog window (e.g. to reduce flickers from child windows resize), then, with the default XP theme, mouse hover on the minimize button or mouse down on the close button will have no visual feedback. It seems that the back buffer for the non client area does not get updated. One obvious workaround is to only add WS_EX_COMPOSITED on WM_ENTERSIZEMOVE and remove it on WM_EXITSIZEMOVE.

What if WS_EX_LAYERED is also set? The above workaround will not work, and worse, the client area will have all sorts of update problems: edit window will not show or receive blinking insertion point, push button will not show sunken/raised border on mouse down/up. Again it seems that the back buffer is not updated. Yet another obvious workaround is to only add WS_EX_LAYERED on WM_ENTERSIZEMOVE and remove it on WM_EXITSIZEMOVE.

What's next? I'm waiting to be hit by more poorly documented styling bugs.