Windows 3.1 Device Drivers (ddag31qh.hlp) (Table of Contents; Topic list)
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Windows for Pen Computing Compatibility
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Microsoft Windows for Pen Computing includes tablet drivers for input from a
handwriting stylus device. An application can use the Windows 3.1
GetMessageExtraInfo function to distinguish between a mouse-generated event
(the return value is 0L) and a stylus generated mouse event (the return
value is non-zero).
 
Tablet drivers use the SI and DI registers to communicate extended event
information to Windows. For this reason, mouse drivers should set these
registers to zero before a function calls the Mouse_Event function in the
Windows 3.1 USER module. This will allow Windows and Pen-Computing based
applications to distinguish between mouse and tablet events.
 
 
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