Q31149: Mouse-Cursor State and EGA Memory
Article: Q31149 Product(s): See article Version(s): 6.x Operating System(s): MS-DOS Keyword(s): ENDUSER | | mspl13_basic Last Modified: 28-JUN-1988 The Microsoft Mouse driver EGA interface maintains the mouse-cursor state in the unused 8K of video memory available at the top of the four 64K buffers that comprise the 256K of total video memory available on a loaded EGA adapter. Normally this is of little consequence in programming such systems; however, if you resize the video buffer by reprogramming the CRT Controller's Offset register, problems may occur. You will know there is a problem if garbage appears on the display after panning through an enlarged virtual screen. To work around this problem, do not use Mouse Function 1 to show the mouse cursor. Instead, use an alternative method of monitoring the mouse's screen location (e.g. XOR some graphical object to the screen).
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