Programmer Power Tools/Programmer Power Tools.iso/screen/xflash1.arc/XFLASH.ASM

Assembly Source File | 1987-03-17 | 10.9 KB | 433 lines

; XFLASH by David Hite     -    Optimized for 8088 Processor
; Eliminates the flash that occurs during scrolling on the CGA.
; XFLASH is FreeWare.

; Your machine may be able to move more characters or fewer
; characters during vertical retraces than mine.
; You can experiment by changing the values of max_vert and clr_max_vert.
; Max_horiz will probably not need to be changed, because it is
; based on the CGA's 200 scan lines.

; The difference between XFLASH and XFLASH-2, other than the different
; values for max_vert and clr_max_vert, is that XFLASH-2 moves a word
; during the horizontal retrace, while XFLASH can only move a byte.
; The code is therefore slightly different.

clr_max_vert    equ    420        ; the maximum number of words to
                        ; clear during a vertical retrace
max_vert        equ    210        ; the maximum number of words to move in
                        ; a vertical retrace
max_horiz    equ    196        ; must be an even number!
                        ; the maximum number of horizontal retraces
                        ; to be used for moving 1 byte between
                        ; vertical retraces.  This is set to just
                        ; less than the number of scan lines so that
                        ; the next vertical retrace is not missed.
                        ; Increasing this value can actually slow the
                        ; program down because it will have to wait
                        ; longer for the next vertical retrace.

vstat        equ    3dah            ; the video status register
v_retrace    equ    00001000b        ; vertical retrace bit mask
h_retrace    equ    00000001b        ; horizontal retrace bit mask


cseg    segment para public 'code'
    assume cs:cseg,ds:cseg,ss:cseg,es:nothing
    org    100h

start:
    jmp install                ; install the program

savestack    dw    0,0
request        dw    0            ; ax from interrupt
fill_attrib    dw    0            ; bx from interrupt
video_handler dd    0            ; address of the original video handler
apage        db    0            ; active video page
amode        db    3            ; active video mode
display_seg     dw     0b800h        ; addr of cga display memory

new_video_int proc far            ; far label since it's entered by interrupt
                            ; and thus must generate inter-segment ret
    sti                        ; enable interrupts

    cmp    ah,0                    ; check for mode switch
    jne    chk_mode
    mov    cs:amode,al            ; remember new mode
    jmp    short not_ours            ; and let bios change the mode

chk_mode:
    cmp    cs:amode,3            ; we don't scroll graphics modes
    jg    not_ours

chk_5:
    cmp    ah,5                    ; check for page switch
    jl    not_ours
    jne    chk_6
    mov    cs:apage,al            ; remember new page number
    jmp    short not_ours            ; and let bios change the page

chk_6:
    cmp    ah,6
    jne    chk_7
chk_6a:
    cmp    cl,0                    ; we do it only for complete lines
    jne    not_ours
    cmp    dl,79
    jne    not_ours
    jmp    short scroll

chk_7:
    cmp    ah,7
    je    chk_6a

not_ours:
    pushf                ; emulate int instruction
    call dword ptr    [cs:video_handler]
    iret

scroll:
    mov cs:savestack,sp
    mov cs:savestack+2,ss

    mov    cs:request,ax
    mov    ax,cs
    mov    ss,ax
    mov    sp,100h

    push bp                ; set up a stack frame
    mov    bp,sp
    sub    sp,0eh
    call savereg
    mov    ds,ax
    mov    ax,request

    call    main                ; that's where the work is done

    call restreg
     add    sp,0eh
    pop    bp

    mov ss,cs:savestack+2
    mov sp,cs:savestack

    iret                ; return from interrupt

new_video_int    endp

inside proc near
fix_ch0:
    mov    ch,0
    jmp    short chk_dh
fix_ch24:
    mov    ch,24
    jmp    short chk_dh
fix_dh0:
    mov    dh,0
    jmp    short chk_al
fix_dh24:
    mov    dh,24
    jmp    short chk_al
fix_al25:
    mov    al,25
    jmp    short regs_ok

main:
    mov    fill_attrib,bx        ; save fill attribute for much later (clr_area)
    push    dx                ; because MUL uses it
    cmp    ch,0
    jl    fix_ch0
    cmp    ch,24
    jg    fix_ch24
chk_dh:
    cmp    dh,0
    jl    fix_dh0
    cmp    dh,24
    jg    fix_dh24
chk_al:
    mov    ax,request
    cmp    al,0
    jle    fix_al25
    cmp    al,25
    jg    fix_al25
regs_ok:
    mov    request,ax        ; in case we fixed it
    xor    bh,bh
    mov    bl,apage            ; get the current page number
    mov    ax,4096            ; the size of a a page
    mul    bx                ; multiply by the page number to get offset
    mov    di,ax            ; and put it in the destination index
                        ; now calculate the offset of the window
    mov    bl,ch            ; by getting the starting row
    xor    bh,bh
    mov    ax,160            ; we only handle full rows
    mul    bx                ; and multiply by chars/row to get offset
    add    di,ax            ; and adding to di to get address
    mov    ax,di
    mov    si,ax            ; and put it in the source index as well
    pop    dx
    mov    ax,request        ; get the original request
    mov    bh,dh            ; move bottom line to bh
    sub    bh,ch            ; subtract top line
    inc    bh                ; bh now has number of lines in window

    cld                    ; we'll move forward unless scroll is down
    mov    es,display_seg
    cmp    al,0                ; clear the area?
    jbe    m_1                ; yes
    cmp    al,bh
    je    m_1b                ; we are clearing all the lines
    jb    m_2                ; we are clearing some of the lines
m_1:                    ; we are clearing more than all the lines!
    mov    al,bh            ; move number of lines in window to al
    mov    request,ax
m_1b:
    jmp    clr_area

m_2:                    ; bh has lines in window, al has lines
                        ; to scroll
    cmp    ah,6                ; up or down?
    je    up
down:                    ; we are scrolling down
    std                    ; so we move backwards

    sub    al,bh            ; the source is bh-al lines below si
    neg    al                ; correct the sign
    cbw                    ; convert to a word
    mov    cx,160
    mul    cx                ; multiply by chars/row
    sub    ax,2                ; subtract a word to get end of line
    add    si,ax            ; and add to si, the address of the up left

    ; the destination is the lower right which is bh lines
    ; below current di => di = di + bh*160 - 2

    mov    al,bh            ; get lines in window into al
    cbw
    mov    cx,160
    mul    cx
    sub    ax,2                ; subtract a word to get end of line
    add    di,ax            ; di now has address of destination

    jmp    short movem

up:                        ; we are scrolling up
    ; the source is al lines below si which is al*160 chars below current si

    cbw                    ; gets number of lines into ax
    mov    cx,160
    mul    cx
    add    si,ax            ; si now has address of source

    ; the initial destination is correct, we don't need to change it

movem:                    ; now start to move words
    ; fix bx such that it is number of words to move
    ; = (number of lines in window minus number of lines to scroll)*80

    mov    ax,request        ; get number of lines to scroll
    cbw                    ; slightly faster than xor ah,ah
    sub    al,bh            ; subtract lines in window from lines to scroll
    neg    al                ; after correcting the sign, ax has lines to move
    mov    cx,80            ; words/line
    mul    cx                ; multiply to get words to move
    mov    bx,ax            ; bx now has number of words to move

    push    ds                ; we're about to change it to display_seg
    mov    dx,vstat            ; the video status register
    mov    ds,display_seg        ; load address of display segment

mvm_vert:                ; first wait for a vertical refresh
    mov    cx,bx            ; move words remaining to cx
    cmp    cx,max_vert        ; too  many?
    jle    mvm_many            ; no, go move'm
    mov    cx,max_vert        ; yes, move max_vert more, maximum
mvm_many:
    sub    bx,cx            ; that many will remain when rep movsw ends

mvm_v_refresh:
    in    al,dx
    test    al,v_retrace
    jnz    mvm_v_refresh        ; wait for a non retrace period

mvm_v_wait:
    in    al,dx            ; get the retrace status
    test    al,v_retrace        ; check for retrace in progress
    jz    mvm_v_wait        ; wait until retrace

    ; in a vertical retrace, we can move many
    rep    movsw
    cmp    bx,0
    je    mvm_end

    mov    cx,max_horiz
    shl    bx,1                ; to convert words to bytes
mvm_1:
    dec    bx
mvm_h_refresh:
    in    al,dx
    test    al,h_retrace
    jnz    mvm_h_refresh        ; wait for a non retrace period

;    the next statement is commented out to prevent comm char loss
;    cli                    ; disable interrupts while waiting (not long)
mvm_h_wait:
    in    al,dx            ; get the retrace status
    test    al,h_retrace        ; check for retrace in progress
    jz    mvm_h_wait        ; wait until retrace

    movsb                ; now move one byte
;    sti                    ; and now enable interrupts again

    cmp    bx,0                ; are we finished?
    je    mvm_end
    loop    mvm_1            ; only if cx not 0
    cmp    bx,0
    je    mvm_end

mvm_do_cx_again:
    shr    bx,1                ; convert back to words
    mov    cx,bx            ; move words remaining to cx
    cmp    cx,max_vert        ; too  many?
    jle    mvm_h_many        ; no, go move'm
    mov    cx,max_vert        ; yes, move max_vert more, maximum
mvm_h_many:
    sub    bx,cx            ; that many will remain when rep movsw ends
    jmp    mvm_v_wait

mvm_end:                    ; we've finished moving
    pop    ds                ; restore the data segment

clr_area:
;    we're now ready to blank the number of lines that were scrolled.
;    The direction flag and di and es are set correctly, given
;    what we've done so far.  All we need to do is calculate number of
;    words to blank.

    mov    ax,request        ; to get number lines to scroll
    cbw
    mov    cx,80            ; words/line
    mul    cx                ; ax now has words to blank
    mov    bx,ax            ; put it in bx

    mov    dx,fill_attrib        ; dh now has the fill attribute
    mov    dl,' '            ; move a space to dl

    mov    si,dx            ; move clear char to si

;    the following code sets the screen border to the fill attribute.
;    un-comment it if you want to do this
;    mov    cl,4
;    shr    dh,cl
;    mov    al,dh
;    or    al,20h
;    mov    dx,03d9h            ; set border to fill attribute
;    out    dx,al
;    end of set border code

    mov    dx,vstat            ; the video status register

clr_vert:                ; first wait for a vertical refresh
    mov    cx,bx            ; move words remaining to cx
    cmp    cx,clr_max_vert    ; too  many?
    jle    clr_many            ; no, go move'm
    mov    cx,clr_max_vert    ; yes, move clr_max_vert more, maximum
clr_many:
    sub    bx,cx            ; that many will remain when rep stosw ends

clr_v_refresh:
    in    al,dx
    test    al,v_retrace
    jnz    clr_v_refresh        ; wait for a non retrace period

clr_v_wait:
    in    al,dx            ; get the retrace status
    test    al,v_retrace        ; check for retrace in progress
    jz    clr_v_wait        ; wait until retrace
    xchg    ax,si
    rep    stosw
    xchg    ax,si
    cmp    bx,0
    je    clr_end

    mov    cx,max_horiz
clr_1:
    dec    bx
clr_h_refresh:
    in    al,dx
    test    al,h_retrace
    jnz    clr_h_refresh        ; wait for a non retrace period

;    the next statement is commented out to prevent comm char loss
;    cli                    ; disable interrupts while waiting (not long)
clr_h_wait:
    in    al,dx            ; get the retrace status
    test    al,h_retrace        ; check for retrace in progress
    jz    clr_h_wait        ; wait until retrace
    xchg    ax,si
    stosw                ; now move one word
;    sti                    ; and now enable interrupts again
    xchg    ax,si
    cmp    bx,0                ; are we finished?
    je    clr_end
    loop    clr_1
    cmp    bx,0
    je    clr_end

clr_do_cx_again:
    mov    cx,bx            ; move words remaining to cx
    cmp    cx,clr_max_vert    ; too  many?
    jle    clr_h_many        ; no, go move'm
    mov    cx,clr_max_vert    ; yes, move clr_max_vert more, maximum
clr_h_many:
    sub    bx,cx            ; that many will remain when rep movsw ends
    jmp    clr_v_wait

clr_end:                    ; we've finished moving

    cld                    ; just for the heck of it
    ret


savereg:
    mov    -2[bp],bx
    mov    -4[bp],cx
    mov    -6[bp],dx
    mov    -8[bp],si
    mov    -0ah[bp],di
    mov    -0ch[bp],ds
    mov    -0eh[bp],es
    ret
restreg:
    mov    bx,-2[bp]
    mov    cx,-4[bp]
    mov    dx,-6[bp]
    mov    si,-8[bp]
    mov    di,-0ah[bp]
    mov    ds,-0ch[bp]
    mov    es,-0eh[bp]
    ret
inside    endp

install:

    mov ax,3510h            ; get interrupt 10 vector
    int 21h
    mov word ptr video_handler,bx
    mov word ptr video_handler+2,es

    mov ax,2510h
    mov dx,offset new_video_int    ; now put our routine there
    int 21h

    mov dx,offset install    ; terminate and stay resident
    mov cl,4
    shr dx,cl
    inc dx                ; round up
    mov ah,31h
    int 21h


cseg ends
    end start