Auto-Panning Windows 2

This code provides a simple way of adding full AutoScroll capability
to pretty much any window, I have provided a demo program which also incorporates
the all of the code you need. I believe it works the same way as Internet
Explorer, that is all of the behaviour I have seen from IE. The cursor
changes in every direction just as it does in IE, it uses the pointers
and origin bitmaps pretty much the same as IE, these are the cursors and
bitmaps supplied with the Intellipoint SDK with slight modificatiosn to
the bitmaps.

How to use it

OWnd is a DLL, I did it this way because it seemd the easiest way to use
it without having to copy resource fiels etc all over the place, plus it
really is a component that is shared amongst projects. Simply include the
OWnd DLL project  in as a subproject of yours, include the OWndDLL.h
file in your relevant source files and call StartPanning(…) in your OnMButtonDown
message handler. That’s it really.

Additionally you can respond to the registered message OWND_WINDOW_UPDATE
if you want to perform extra scrolling, the registered message  is
sent every time a scroll event is issued, your message handler should look
something like this:

static const UINT uOriginWindowUpdateMessage = ::RegisterWindowMessage( OWND_WINDOW_UPDATE );

LRESULT CPanningWindowView::OnOriginWindowUpdate(WPARAM , LPARAM lParam)
// Process the update message sent by the origin window.
// You only need to respond to this message if you want to do extra or different scrolling
    // psizeDistance will contain the distance the cursor is from the origin. We then use
    // this to calculate the new scroll position and the amount to scroll our window.
    const CSize *psizeDistance = reinterpret_cast<const CSize *>( lParam );
#ifdef _DEBUG
#endif // _DEBUG
    // Return 1 to signal to COriginWnd that you have handled the scrolling, return 0 if you
    // want COriginWnd to perform the scrolling.
    return 0;

The demo project shows all of this behaviour in the source file PanningWindowView.cpp.

This code imroves over the other examples posted to codeguru in the
following areas:

  • Much closer emulation of IE behaviour, I have tried to do exactly as IE

  • More easily extended and altered, the other examples have way too many
    hardcoded values scattered throughout the code.

  • Compiles at level four warnings with warnings as errors, it has been linted
    and it has been built and tested in UNICODE

  • Less code.

Please let me know of any bugs, fixes or modifications.

Download demo project and source code – 42KB

Date Posted: 6/24/98

Posted by: Pat Laplante.

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