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
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 dx,offset my_proc
mov cx,flags ;each bit is explained later
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
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:
;ax=condition that triggered call (same as flags above)
;bx=button state (bit 0=left; 1=right)
;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 !
- 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.
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
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