Mouse Callback

One of the most useful routines is an Interrupt callback.
The ability to receive an instruction triggered by an interrupt enables users to continue working until the interrupt occurs.

The most usefull of these is the mouse interrupt. The mouse uses interrupt 33h.

The following code example show how to start the callback procedure and how to handle it.

This code tracks the movement by displaying a yellow symbol on a text display.
When a button is pressed it diplays the AX, BX, CX and DX registers at the current mouse position.

In the screen shot below the 4 registers show these values, A left button click starting with a 2 button down and folowed by the button up.
Then the right button click starting with an 8. The mouse symbol here is a yellow X.

The callback routine handling the request must return as a FAR RET for locall calls or an IRET for drivers in a different segment.

Initialize and Register the mouse callback handler.

To start a callback the mouse drivers must be Initialized, and then register the address of the callback routine.

; Start the Mouse Callback procedure ; Set CX=Hex value corresponding to these bits ; 0=mouse pointer moved ; 01h ; 1=left button pressed ; 02h ; 2=left button released ; 04h ; 3=right button pressed ; 08h ; 4=right buttom released ; 10h ; 5=center buttom released ; 20h ; 6=center buttom released ; 40h SubMouseStartCallBack: PUSHA MOV AX, 0x0000 ; Initialize Mouse INT 0x33 MOV CX, 0x007F ; Request all mouse actions or just those required MOV DX, SubMouseCallBack ; Specify the callback routine MOV AX, 0x000C ; Register the callback request INT 0x33 POPA RET

Handle the Mouse Callback.

The callback handler should either handle the request itself or pass the request to an appropriate sub routine.
This example compares the mouse action in AX and redirects the callback to the correct sub routine.

; Process Mouse Callback by calling the associated sub routines SubMouseCallBack: PUSHA CMP AX, 0x0001 JE SubMouseMoveCallBack ; Move and Wheel CMP AX, 0x0002 JE SubMouseLeftCallBack ; Down CMP AX, 0x0004 JE SubMouseLeftCallBack ; Up CMP AX, 0x0008 JE SubMouseRightCallBack ; Down CMP AX, 0x0010 JE SubMouseRightCallBack ; Up CMP AX, 0x0020 JE SubMouseCentreCallBack ; Down CMP AX, 0x0040 JE SubMouseCentreCallBack ; Up POPA RETF ; Far return

Handle Mouse Movement

Tracking the mouse is relatively easy with the callback. Every movement of the mouse triggers a callback.
The CX register holds the horizontal position (usually multiplied by 8 pixels).
The DX register holds the vertical position (usually multiplied by 8 pixels).

; Displays Mouse moves and displays ; a cursor symbol ; Returns CX=Horizontal, DX=Vertical SubMouseMoveCallBack: PUSHA PUSH CS POP DS PUSH CS ; Reset ES and DS to local CS code section POP ES PUSH EDX PUSH ECX MOV CX, 0x2607 ; Turn off the text cursor MOV AX, 0x0100 INT 0x10 MOV CX, 0x0001 ; blank the contents at the current text position MOV BX, 0x0000 ; Colour Black on Black MOV AX, 0x0908 ; Backspace character INT 0x10 POP ECX POP EDX SHR CX, 0x03 ; divide Colunm by 8 to get text column SHR DX, 0x03 ; divide Row by 8 to get text row SHL DX, 0x08 ; Set up DX (DH=Colunm,DL=Row) MOV DL, CL MOV AX, 0x0200 MOV BX, 0x0000 INT 0x10 MOV CX, 0x0001 ; Display one character MOV BX, 0x000E ; Set colour Yellow on Black MOV AX, 0x09CF ; Display a symbol to show the cursor INT 0x10 POPA RETF ; Far return

Handle Mouse Button Presses.

The mouse button clicks are reported on button down and button up. These can be detected independantly when required.
This example passes them to the same routine.

The callback provides the following registers. AX=Mouse Action, BX=Mouse Down or Up, CX=Horizontal position, DX=Vertical position.

The left and right mouse buttons are handle in the same way.

; Displays Mouse button presses ; Returns AX=(2=Mouse Down,4=Mouse Up) ; BX=(1=Mouse Down,0=Mouse Up) ; CX=Horizontal position ; DX=Vertictal position SubMouseLeftCallBack: PUSHA ; Recover the DS and ES registers if they are needed. ; They will have been changed by the callback interrupt process. PUSH CS POP DS PUSH CS POP ES ; Do something with the button click ; or Display AX, BX, CX, DX, SI and DI POPA RETF ; Far return

Cancelling the Callback.

You can cancel the callback by registering the callback again with CX set to NULL.

; Cancel the Mouse Callback procedure SubMouseCancelCallBack: PUSHA MOV CX, 0x0000 MOV AX, 0x000C INT 0x33 POPA RET

Last Update 9/03/2023