Bresenham line....I think

Ok, prepare to be amazed by what you are about to see....A LINE DRAWER... Very Happy

DO NOT in any shape, way, or form look deeply into the drawer code because it is such a mess your eyes may explode...Thank you
Can anyone help with the flicker? I know it has to do with vertical retrace, but anywhere i put in a retrace wait it just makes things worse.

BTW, I know there are many errors(like not clearing the kbd buffer, it has been pointed out to me in other threads) but I dont care, This was made to run on my computer as a test, so I didn't care about things like that.

Code:

org 100h

push 0a000h
pop es

mov ax,13h
int 10h

start:
call mouse
call line
call cls

key:
in al,60h
dec al
jnz start
mov ax,03h
int 10h
ret

cls:
        mov cx,0FA00h
        mov al,0
        rep stosb
        ret

mouse:
        pusha
        mov     ax,03h
        int 33h
        shr     cx,1h
        mov     [x2], cx
        mov     [y2], dx
        popa
        ret

line:
        pusha
        mov     ax, [y1]                   
         mov     bx, 320                 
        mul     bx                      
        add     ax, [x1]                
        mov     di, ax                  

        mov     ax, [x2]
        cmp     ax, [x1]
        jae     @1
        sub     [xo], 1
        mov     ax, [x1]
        sub     ax, [x2]
        mov     cx, ax
        jmp     @2
@1:
        mov     ax, [x2]              
        sub     ax, [x1]
        ;mov     cx, ax                  
@2:
        mov     bx, [y2]
        cmp     bx, [y1]
        jae     @3
        sub     [yo],1
        mov     bx, [y1]
        sub     bx, [y2]
        jmp     @4
@3:
        mov     bx, [y2]                
        sub     bx, [y1]
@4:
        cmp     ax, bx
        jae     abc123
        jmp     line1

abc123:
        mov     cx, ax
        mov     si, ax                  
        dec     si

        mov     dl, [colour]           

LoopTop:
        mov     [es:di], dl             
        sub     si, bx                  
        jnl     SkipY                   
        cmp     [yo], 0
        je      @5
        add     di, 320                 
        add     si, ax                  
        jmp SkipY
@5:
        sub     di,320
        add     si,ax
SkipY:
        cmp     [xo],0
        je      @6
        inc     di
        jmp     @7
@6:
        dec     di
@7:
        dec     cx                     
        jnz     LoopTop                 
        popa
        mov     [xo], 1
        mov     [yo], 1
        ret

line1:
        mov     cx, bx
        mov     si, bx                
        dec     si

        mov     dl, [colour]        

LoopTop1:
        mov     [es:di], dl          
        sub     si, ax                
        jnl     SkipX1                 
        cmp     [xo], 0
        je      @51
        inc     di                   
        add     si, bx                
        jmp SkipX1
@51:
        dec     di
        add     si,bx
SkipX1:
        cmp     [yo],0
        je      @61
        add     di, 320
        jmp     @71
@61:
        sub     di, 320
@71:
        dec     cx                       
        jnz     LoopTop1              
        popa
        mov     [xo], 1
        mov     [yo], 1
        ret

x1 dw 160
y1 dw 100
x2 dw 0
y2 dw 0
colour db 1
xo db 1
yo db 1