How to : Create a better mouse driver

Written by : Peter Quiring
The mouse driver is good for text modes, CGA and maybe VGA but when it comes to hi-res VESA modes it's not usable, and unreliable. So you need to build your own mouse driver using a special mouse function.

Step 1: Make sure there is a mouse driver

  mov ax,0
  int 33h
  cmp ax,0
  jz no_mouse_driver

If ax is still zero after calling INT 33h then there is no mouse driver and you should quit with an error message if the program needs the mouse driver.

Step 2: Enable the call back thing

  mov ax,0ch
  push cs
  pop es
  mov dx,offset my_proc
  mov cx,flags   ;each bit is explained later
  int 33h

Now my_proc will be called when ever the mouse is moved.
flags: (if these bits are set then my_proc will be called if the condition occurs)

  bit   condition
   0   cursor pos has changed
   1   left button pressed
   2   left button released
   3   right button pressed
   4   right button released
   5-15 not used  (but I believe 2 more must be used if you have a 3 button mouse)

my_proc should look like this:

my_proc proc
  ;ax=condition that triggered call (same as flags above)
  ;bx=button state (bit 0=left; 1=right)
  ;cx=horizontal position
  ;dx=vertical position
  ;si=horizontal mouse count since last call (mickeys)
  ;di=vertical mouse count since last call (mickeys)
..... ;do what ever you need to update the mouse and record the button states
  retf  ;make sure to use ret far !
my_proc endp

Notes:

Ignore AX always. Under Win95 I've noticed it does not properly set the bits (bug?). So just use BX instead for the button status.
CX/DX represent the mouses current pos according to the current resolution on screen, but many times the mouse driver does not know the correct resolution so I suggest you ignore these. In TEXT mode the mouse driver considers each cell (char) on screen to be 8x8 pixels (regardless of what it really is) and CX,DX would represent this.
SI and DI represent the mouses movement from the last time this callback feature was called. This is a SIGNED 16bit value. Unlike CX/DX this value never stops if the mouse hits the edge of the screen. This is good since the mouse driver never works properly anyways.

Step 3 : Disable call back.

  mov ax,0ch
  mov dx,0
  mov es,dx
  mov cx,0
  int 33h

To disable the call back set ES:DX and CX to zero and call INT 33h.
You must disable the call back before quiting or the mouse driver will crash
the system when calling a proc that no longer exists.



That's all it takes...

Now what I have shown here is how it is done in real mode.  To do the same
under PMODE depends on your DOS extender.  Some extenders will extend int 33h
and others do not.  DOS/4GW, PMODE/W and WDOSX do so the code would look
exactly the same as above except you should use ES:EDX.

Please refer to my DOS Extender's Descriptions page for more info on
DOS extenders.







BACK




Copyright © 1995-2005 Nexus Systems 
Privacy