proc OpenFile1
; Open file
    mov ah, 3Dh
    xor al, al
    mov dx, offset filename1
    int 21h
    jc openerror1
    mov [filehandle], ax
    ret
openerror1:
    mov dx, offset ErrorMsg
    mov ah, 9h
    int 21h
    ret
endp OpenFile1

proc ReadHeader
; Read BMP file header, 54 bytes
    mov ah,3fh
    mov bx, [filehandle]
    mov cx,54
    mov dx,offset Header
    int 21h
    ret
endp ReadHeader

proc ReadPalette
    ; Read BMP file color palette, 256 colors * 4 bytes (400h)
    mov ah,3fh
    mov cx,400h
    mov dx,offset Palette
    int 21h
    ret
endp ReadPalette

proc CopyPal
        ; Copy the colors palette to the video memory
        ; The number of the first color should be sent to port 3C8h
        ; The palette is sent to port 3C9h
        mov si,offset Palette
        mov cx,256
        mov dx,3C8h
        mov al,0
        ; Copy starting color to port 3C8h
        out dx,al
        ; Copy palette itself to port 3C9h
        inc dx
    PalLoop:
        ; Note: Colors in a BMP file are saved as BGR values rather than RGB.
        mov al,[si+2] ; Get red value.
        shr al,2 ; Max. is 255, but video palette maximal
        ; value is 63. Therefore dividing by 4.
        out dx,al ; Send it.
        mov al,[si+1] ; Get green value.
        shr al,2
        out dx,al ; Send it.
        mov al,[si] ; Get blue value.
        shr al,2
        out dx,al ; Send it.
        add si,4 ; Point to next color.
        ; (There is a null chr. after every color.)
    loop PalLoop
        ret
endp CopyPal

proc CopyBitmap
        ; BMP graphics are saved upside-down.
        ; Read the graphic line by line (200 lines in VGA format),
        ; displaying the lines from bottom to top.
        mov ax, 0A000h
        mov es, ax
        mov cx,200
    PrintBMPLoop:
        push cx
        ; di = cx*320, point to the correct screen line
        mov di,cx
        shl cx,6
        shl di,8
        add di,cx
        ; Read one line
        mov ah,3fh
        mov cx,320
        mov dx,offset ScrLine
        int 21h
        ; Copy one line into video memory
        cld ; Clear direction flag, for movsb
        mov cx,320
        mov si,offset ScrLine
        rep movsb ; Copy line to the screen
         ;rep movsb is same as the following code:
         ;mov es:di, ds:si
         ;inc si
         ;inc di
         ;dec cx
         ;loop until cx=0
        pop cx
    loop PrintBMPLoop
        ret
endp CopyBitmap