video.s

;--- BEGIN ---------------------------------------------------;

;--- DATA ----------------------------------------------------;

SEGMENT .data

vpage:      db 00       ; current video page
vbase:      dw 0b800h   ; text area (next page = 0b900h?)
pixbase:    dw 0a000h   ; graphics mode area

;--- CODE ----------------------------------------------------;

SEGMENT .text

DiscoverVidBase:
%ifdef DISPLAY_PAGES
                mov ax, 0500h    ; SELECT ACTIVE DISPLAY PAGE -> 0
        int 10h
%endif
        mov ah, 15       ; GET CURRENT VIDEO MODE, ah -> col, al -> mode, bh -> active page
        int 10h
        cmp al, 7
        jne .UseDefault
        mov [vbase], word 0b000h
.UseDefault:    ret

TextVidBase:    mov es, [vbase]
        ret

PixVidBase: mov es, [pixbase]
        ret

        ; TODO: determine if the text video page is already active;
        ; if so, only swap pages with TextVidPage.
        ; this will reduce flicker on return to OS from application.

TextVid:
%ifdef DISPLAY_PAGES
                mov     ax, 0003h
            int 10h
        mov     ax, 0500h
        int 10h
        mov [vpage], byte 0
%endif
%ifdef DISPLAY_PAGES
        mov ax, ds
        mov es, ax
        mov ax, 1100h
        mov bp, offset charset
        mov cx, 256     ; num of chars to be reimaged
        mov dx, 0       ; first char num to be reimaged
        mov bl, 0       ; block to load in "map 2"
        mov bh, 16      ; bytes per char-image
        int 10h
%endif
        call    TextVidBase
            call    OKLight
        call    RefreshStatus
        jmp DisplayPage


PixVid:         mov     ax, 0013h
            int 10h
            jmp PixVidBase


NextTextVidPage:
%ifdef DISPLAY_PAGES
                mov al, [vpage]
        inc al
        and al, 7
        mov [vpage], al
        mov     ah, 05h
        int 10h
        ; TODO: change vid base
%endif
        ret


PrevTextVidPage:
%ifdef DISPLAY_PAGES
                mov al, [vpage]
        dec al
        and al, 7
        mov [vpage], al
        mov     ah, 05h
        int 10h
        ; TODO: change vid base
%endif
        ret

ClrScreen:  mov bh, cl
        xor cx, cx          ; (0,0)-
        mov dx, 184fh       ; (79,24)
        mov ax, 0600h       ; BIOS clear rectangle
        int 10h
        ret


;--- END -----------------------------------------------------;