Apple II
Technical Notes
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                                                  Developer Technical Support

Apple IIgs
#85:    Moving the Mouse

Written by:    Matt Deatherage                                      July 1990

This Technical Note discusses moving the cursor on the screen without touching 
the mouse.
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It is sometimes desirable to programmatically move the QuickDraw II cursor on 
the screen without requiring the user to touch the mouse.  This can be 
effective, for example, in tutorial software that actually shows mouse actions 
such as pulling down menus and dragging windows.

There is not an easy or obvious way to do this in the toolbox.  This is not a 
bad thing; it prevents overzealous programmers from zapping the mouse all over 
the screen for suspicious reasons.  You must remember that the mouse belongs 
to the user, not to the application.  If the user has put the mouse somewhere, 
it should only be a user's action that causes the cursor to move elsewhere.  
Most of the time that action is touching the mouse and physically moving it.  
Do not move the mouse except in response to a user-initiated command.

The most obvious way to move the mouse position--calling PosMouse with the new 
mouse position--is not sufficient; PosMouse does not update the current mouse 
position.  When the mouse is next moved, a mouse interrupt comes through and 
the new deltas are added to the old mouse position, resulting in correct 
ReadMouse results after the mouse has been physically moved.  Also, PosMouse 
does not update the cursor on the screen.

Faking Out the System 

When you wish to move the mouse yourself, you are in effect replacing (or 
adding to) the standard mouse with a small programmatic mouse substitute--your 
code.  This qualifies as a "device" and can be considered an Event Manager 
"device driver."  You can then make the appropriate Event Manager call, 
FakeMouse.  When calling FakeMouse, you supply all the mouse information 
yourself, allowing you to move the mouse, simulate button presses, and in 
general replace the mouse.

Further Reference
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  o  Apple IIgs Toolbox Reference, Volumes 1-3