INT 33H: Mouse Support

  0000H Reset/Query driver presence  0013H Set max for speed doubling
  0001H Display pointer              0014H Exchange event handlers
  0002H Hide pointer                 0015H Query status buffer size
  0003H Query position & buttons     0016H Save mouse status
  0004H Move pointer                 0017H Restore mouse status
  0005H Query button-pressed count   0018H Install mouse+key event handler
  0006H Query button-released count  0019H Get addr of mou+key evt handler
  0007H Set horizontal range         001aH Set mouse sensitivity
  0008H Set vertical range           001bH Query mouse sensitivity
  0009H Set graphics pointer shape   001cH Set mouse interrupt rate
  000aH Set text pointer mask        001dH Set display page
  000bH Query last motion distance   001eH Query active display page
  000cH Set event handler            001fH Deactivate mouse driver
  000dH Enable lightpen emulation    0020H Activate mouse driver
  000eH Disable lightpen emulation   0021H Reset mouse driver
  000fH Set pointer speed            0024H Query mouse type, IRQ#
  0010H Set exclusion area

  To access the mouse support: load the registers as described under each
  function, set AX to the function number, and execute INT 33H.

  In most text-mode applications, very few functions are actually needed.
  In a graphics mode application, you had better stick to the Windows or
  other GUI or TUI environment mouse support.

  To determine if the mouse is present, use INT 33H 0000H.  This resets the
  mouse driver and, in general, all of the default settings are adequate.
  Note that you can probably assume that the user knows how to install the
  mouse (via executing MOUSE.COM or installing MOUSE.SYS in CONFIG.SYS).

  You may poll for mouse activity via INT 33H 0003H or install an event
  handler via INT 33H 000cH or INT 33H 0018H and take action whenever a
  button gets pressed.  A common technique is to have your event handler
  simply set values into global variables which can be examined by any part
  of your program at any time.

  One thing to note is that all screen coordinates used by the driver are
  specified as if the screen were in a "virtual graphics mode".  For text-
  mode applications, a character position is considered to be 8 points wide
  and 8 points tall.  Thus, to specify a screen (X,Y) of (10,11), pass the
  value (80,88).  Similarly, when the support indicates that the mouse is at
  (632,80), then the pointer is actually on character (79,10).  Just divide
  each coordinate by 8 (or shift right 3 times).

█▌Mouse Droppings▐█
  One tricky part of text-mode mouse programming relates to an effect I call
  mouse droppings.  When you perform direct writes to the video buffer (and
  in doing so, overwrite the position of the mouse), the mouse support won't
  know about any new character or attribute at the pointer position.  When
  the mouse is then moved, the driver will restore the old character and
  attribute instead of the new one you have written.

  To avoid this, you must use INT 33H 0002H (hide ptr) before writing
  directly to the video RAM and use INT 33H 0001H (show ptr) afterward.
  Note that if you stick to INT 10H video I/O, you won't have this problem,
  since the mouse support intercepts such I/O calls and eliminates the

█▌TSR Programs▐█
  When writing a TSR which uses the mouse, you must take care to avoid the
  mouse-droppings problem, as well as related problems having to do with
  interrupting an executing program.

  When installing your TSR, call INT 33H 0015H and allocate a buffer of the
  indicated size.  When the TSR is popped up, you must use INT 33H 0016H to
  save the state of the mouse, and use INT 33H 000cH, INT 33H 0014H, or
  INT 33H 0018H to install your event handler.  Upon exiting from your TSR,
  you must use INT 33H 0017H to restore the mouse state for the interrupted

  The Microsoft Mouse is the industry standard and it is generally okay for
  an application to assume that the mouse is 100% Microsoft compatible.

  MS Mouse driver version 6.0 (circa 1983) supported only MouFns 0-17H and
  1dH-1eH.  Driver version 6.1 (circa 1984) supports all the functions
  listed above, adding the ability to install a more flexible event handler
  (check for Shift-, Ctrl-, or Alt- clicks), CRT page awareness, mouse
  sensitivity control, and a way to disable the mouse driver.

  Since all of these improvements have existed for several years (with
  nothing new, to speak of), there should be no problem with using any of
  the newer functions.  However, a few  non-Microsoft mouse devices do not
  support the later fns.  For best compatibility, you might try sticking
  with fns 0000H-0017H.

See Also: API Service Index
          INT 15H 84H (joystick support)
          IRQs: Hardware Interrupts
          DOS Functions