Q31747: INFO: Changing the Mouse Cursor for a Window

Article: Q31747
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly kbInput kbMouse kbSDKPlatform kbWndw
Last Modified: 09-JUN-1999

3.00 3.10
WINDOWS
kbprg

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
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SUMMARY
=======

There are two different methods that an application can use to change the mouse
cursor in a window:

- The application can use the SetCursor function, which will change the mouse
  cursor immediately.

- The application can use the SetClassWord function to change the mouse cursor
  for all windows of a particular window class. This method affects the mouse
  cursor only while it resides within the client area of a window of that
  class.

This article provides additional details regarding these two methods.

MORE INFORMATION
================

A number of factors should be considered during the design of an application
that changes the mouse cursor. The major consideration is that Windows sends the
WM_SETCURSOR message any time the mouse cursor moves on the screen. Normally,
Windows sends the message to the window "under" the mouse cursor. However, if a
window sets the mouse capture, using the SetCapture function, that window
receives all mouse messages, without regard to the position of the mouse
cursor.

When an application calls SetCursor, the mouse cursor changes to reflect the
cursor specified in the call. The cursor retains that shape until SetCursor is
called again, either explicitly by the application, by the DefWindowProc
function, or by another application.

Because Windows is a nonpreemptive multitasking environment, no other application
will gain control of the processor until the application that has the processor
releases it. If the application calls one of a number of Windows functions, it
can potentially lose control of the processor. For a list of Windows functions
that can cause control of the processor to pass between applications, search on
the following words in the Microsoft Knowledge Base:

  prod(winsdk) and nonpreemptive and multitasking

When the DefWindowProc or DefDlgProc function processes a WM_SETCURSOR message,
it calls SetCursor to change the cursor to the default cursor for the
application's window.

The application can prevent the cursor from changing by processing the
WM_SETCURSOR message. A typical application that processes WM_SETCURSOR will
have a global variable for the handle to the current cursor. When the
application receives a WM_SETCURSOR message, it checks the global variable. If
the variable is NULL, the application passes the WM_SETCURSOR message to
DefWindowProc. Otherwise, the application calls SetCursor with the value in the
global variable. To return the cursor to the window default cursor, set the
global variable to NULL.

When Windows sends a WM_SETCURSOR message, it places the hit-test area code into
the low-order word of the lParam parameter. The application can use the hit-test
area code to determine what particular portion of the window is "under" the
mouse cursor. For more information on the hit-test area codes, see the
documentation for the WM_NCHITTEST message in the "Microsoft Windows Software
Development Kit Reference Volume 1."

Additional query words: 3.00 3.10 RegisterClass

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Keywords          : kb16bitonly kbInput kbMouse kbSDKPlatform kbWndw 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbinfo

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