; program with keyboard handler

.model small
.486
.stack 100h

.data

Hitime	EQU 1h		; delay time constants (approximate 1/10 sec.)
Lotime  EQU 8000h
hdtime	equ 10		; 1/100 seconds, used by delay2

rows	dw 9            ; variables to store size of bitmap
columns	dw 24
kbd     dd ?

; use this 24x9 bit map for the shape of a flying saucer (you can 
; change it of course).  Can you figure out a way to interpret 00 as
; transparent instead of as color black?
shape	db 9,0,24,0
	db 00,00,00,00,00,00,00,00,00,00,04,04,04,04,04,00,00,00,00,00,00,00,00,00
	db 00,00,00,00,00,00,00,00,04,04,04,04,04,04,04,04,04,00,00,00,00,00,00,00
	db 00,00,00,00,00,00,00,00,04,04,04,04,04,04,04,04,04,00,00,00,00,00,00,00
	db 00,00,00,00,00,00,04,04,04,04,02,04,02,04,02,04,04,04,04,00,00,00,00,00
	db 00,00,04,04,04,04,04,04,04,04,02,04,04,04,02,04,04,04,04,04,04,04,04,00
	db 00,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04
	db 00,00,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,04,00
	db 00,00,00,00,00,00,00,04,00,00,00,00,00,00,00,00,00,04,00,00,00,00,00,00
	db 00,00,00,00,00,00,04,00,00,00,00,00,00,00,00,00,00,00,04,00,00,00,00,00

buffer	db 216 dup(?)

.code
mymain proc
start: 	mov ax,@data
	mov ds,ax
	mov ax,0a000h	
	mov es,ax
	mov ax,0013h
	int 10h
	call KEYD
	mov cx,150		; x coord
	mov dx,190		; y coord
        mov eax,03000000h
	call BACKGROUND		; draw uniform background
	mov bx, offset shape	; prepare to call drawshape
        call DRAWSHAPE          ; initial shape
	call DELAY
        push ds
        push ax
        push bx
        push es
        mov ax,3509h            ; get location old int 9 handler    
        int 21h
	mov word ptr [kbd],bx
	mov word ptr [kbd+2],es
        mov ax,cs
        mov ds,ax
        mov ax,2509h
        mov dx, offset khandler
        int 21h
        pop es                 ; install my int 9 handler
        pop bx
        pop ax
        pop ds
	
bigd:   mov cx,16000
	call DELAY
	loop bigd
	jmp ENDPROG
mymain endp


; procedures

; my keyboard handler 
khandler:
	sti		; APIC chip disables interrupts
        pushf
        pusha
	push es
        ;mov ax,0a000h
        ;mov es,ax
        in al,60h       ; get code from keyboard
        cmp al,32       ; d key or space?
        jne skip3
        ;call BACKGROUND
        xor ah,ah
        mov cx,ax  
        mov dx,1
        mov bx, offset shape
        call drawshape
skip3:  
        mov ax,@data
        mov ds,ax
	pop es
        popa
        popf
        ; call existing int9 handler:
        jmp ds:[kbd]
        iret

; doesn't draw saucer
DRAWSHAPE proc
	pusha
        mov ax,@data
        mov ds,ax
        mov ax,[bx]    ; save dimensions
	mov di,offset rows
	mov [di],ax
        mov ax,[bx+2]
	mov di,offset columns
	mov [di],ax
	add bx,4	; move to start of real image
	mov ax,320	; compute initial y offset
	mul dx
	add ax,cx	; add x offset
	mov di,ax	; initial destination index
        mov ax,0a000h
        mov es,ax       ; be safe
        mov es:[di],eax ; changed 
	popa
        ret            ; end of procedure  (line 85)
DRAWSHAPE endp	



;The background procedure uses eax as pattern to fill background
BACKGROUND proc
	pushad
	xor di,di
	mov cx,16000
bloop:  mov es:[di],eax
	add di,4
	loop bloop
	popad
	ret
BACKGROUND endp
	
ENDPROG proc 
	 call KEYD
	 mov ax,0003h	;3 reset to text mode
	 int 10h	;3
	 mov ax,4c00h
	 int 21h
ENDPROG endp

; key delay procedure - wait for keypress before continuing
KEYD proc	
	push ax		; save ax register before local use	
	mov ah,1	;k1 DOS interrupt for keyboard input
	int 21h		;k1
	pop ax		; restore ax
	ret		; pop saved instruction address and jump
KEYD endp

DELAY proc	
	push ax		; save registers
	push cx
	push dx
	mov cx,Hitime	; move time to delay into cx:dx
	mov dx,Lotime
	mov ah,86h	; call bios to suspend process
	int 15h
	pop dx		; restore registers and return
	pop cx
	pop ax
	ret
DELAY endp

end