INT 33h AX=0004h: move the mouse pointer — 8086 assembly guide

Put the pointer at CX, DX. The position is clipped to the range set by 0007h/0008h, and in text mode rounded down to a character cell.

INT 33h AX=0004h moves the pointer to a position the program chooses: to the default button of a dialog, back to the centre after a mode change, or under a menu item. The coordinates are in the same virtual-screen pixels INT 33h AX=0003h reports. If the pointer is visible, the driver redraws it at the new place.

The driver does not take the numbers blindly. A position outside the range (set by INT 33h AX=0007h and 0008h, the whole screen by default) is moved to the nearest edge, and in text mode the reported position is rounded down to the cell. The example sets two positions and reads each back:

prints: 96 48 632 192

XOR     AX, AX        ; reset: the range is the whole 640x200
INT     33h
MOV     AX, 0004h     ; move to 100, 50
MOV     CX, 100
MOV     DX, 50
INT     33h
CALL    SHOWP1        ; 96 48: the cell at column 12, row 6
MOV     AX, 0004h     ; far off the screen
MOV     CX, 5000
MOV     DX, 5000
INT     33h
CALL    SHOWP1        ; 632 192: held at the last cell
 
SHOWP1  PROC    NEAR  ; print the mouse position: x y
MOV     AX, 0003h
INT     33h           ; CX = x, DX = y
MOV     BX, DX        ; keep y: printing uses DL
MOV     AX, CX
CALL    PDEC
MOV     DL, " "
MOV     AH, 02h
INT     21h
MOV     AX, BX
CALL    PDEC
MOV     DL, " "
MOV     AH, 02h
INT     21h
RET
SHOWP1  ENDP
PDEC    PROC    NEAR  ; print AX in decimal; keeps every register
PUSH    AX
PUSH    BX
PUSH    CX
PUSH    DX
MOV     BX, 10
XOR     CX, CX        ; digits on the stack
DECD1:
XOR     DX, DX
DIV     BX            ; AX = AX / 10, DX = the last digit
PUSH    DX
INC     CX
TEST    AX, AX
JNZ     DECD1
DECD2:
POP     DX            ; the digits come back first to last
ADD     DL, "0"
MOV     AH, 02h
INT     21h
LOOP    DECD2
POP     DX
POP     CX
POP     BX
POP     AX
RET
PDEC    ENDP

Pitfalls

Moving the pointer does not generate a movement event for the handler installed with INT 33h AX=000Ch, and does not change the mickey counters: it is a jump, not a motion. Coordinates are signed words, so a negative value clips to the left or top edge. Set the range first and the position after, or the position may be clipped by the old range. In DOSBox-X with the host pointer integrated, moving the real mouse over the window right after this call moves the DOS pointer straight back.