;-------------------------------------------------------------------------------
; 2021-02-08 wojtek[at]bitologia.org
; 16-colour palette
;-------------------------------------------------------------------------------

.model tiny
.code
        org 100h
start:  mov ax, 0b800h
        mov es, ax
        xor di, di
        mov ax, 00ffh ; standard CLS (mov ax, 0003h) fills screen with 0
        mov cx, 4000  ; which is replaced by something during the procedure
        cld           ; thus, we must clean the screen with another blank
        rep stosw     ; ASCII=255 instead of ASCII=0

        mov ah, 01h   ; "hide" cursor
        mov cx, 2607h
        int 10h

        mov al, 10h
        mov dx, 3c0h
        out dx, al
        in al, dx
        and al, 00000100b ; do not copy 9th line of ASCII between C0h and DFh
        out dx, al

esc_:   mov cx, 25d   ; 25 lines (80 columns) in 0x03 DOS text mode (8 if jump for every 3)
        xor bx, bx
    xor si, si
draw:   call draw_line_01
        loop draw
        in al, 60h    ;
        cmp al, 1     ;
        jne esc_      ; loop until ESC-pressed
        mov ax, 0003h
        int 10h       ; restore standard ASCII set
        mov ax, 4c00h
        int 21h       ; back to DOS
;------------------------------------------------------------------------------
draw_line_01 proc
        push cx
        push di
        push cs
        pop ds
        push bx
        push cs
        pop es
        mov bp, offset LINE_01  ; start with LINE_01 and skip 80 bytes every loop (~mod 25)
        ; starting with LINE_01 one must jump to the next LINE_02 and so on...
        ; by skipping 80*16 bytes every time
        ; every jump is actually controlled by BX which increases by 10d
        ; hence, it is enough to multiply every offset by 128
        ; that is to shift BX by 7 to the left and finally add the result to BP
        mov cl, 7
        shl bx, cl
        add bp, bx

        mov cx, 240d;
        mov dx, 0d
        mov bx, 1000h
        mov ax, 1100h
        int 10h
        pop bx
        mov ax, 0b800h
        add ax, bx
        mov es, ax
        xor di, di
        ;mov cx, 240d;
        xor al, al
    push bx
    mov bx, offset cmap
load01: mov es:[di], al ; instead of ASCII_MAP - just take consecutive integers from 0 to 240d
        inc al
        inc di
    mov dx, ds:[bx + si]
        mov es:[di], dx; ASCII attribute
    inc bx
        inc di
        loop load01
    pop bx
        pop di
        call slow_down
        call drop_line
        pop cx
        add bx, 10d ; draw (jump to) next line (offset) (30 for "3")
    add si, 80d; (240 for "3")
        ret
draw_line_01 endp
;------------------------------------------------------------------------------
drop_line proc
        push cx
;        push di
        push cs
        pop ds
        mov ax, 0b800h
        add ax, bx
        mov es, ax
        xor di, di
        mov cx, 80d ; (240 for "3")
clear:  inc di                  ; skip ASCII - whatever it is
        mov byte ptr es:[di], 0 ; but reset attribute to zero
	inc di                  ; (ASCII can be anything, because becomes invisible)
        loop clear
;        pop di
        pop cx
        ret
drop_line endp
;------------------------------------------------------------------------------
slow_down proc
        push cx
        xor cx, cx
        mov dx, 0a510h ; wait CX:DX RTC-microseconds
        mov ah, 86h
        int 15h
        pop cx
        ret
slow_down endp