I’m still having problems getting a working floppy drive in my machine.
(Broken FDD card, drive errors etc)

The raster bar (also referred to as rasterbar or copperbar) is an effect used in demos and older video games that displays animated bars of colour, usually horizontal, which additionally might extend into the border, a.k.a. the otherwise unalterable area (assuming no overscan) of the display

I first tried to get it working in DosBOX, but thats a mess.
Good for simple emulation but not hardcore register manipulation.

Below dosbox

Three examples below are in PCem

use16
org 0x100

CRTC_INDEX = 0x03D4
CRTC_DATA = 0x03D5
INPUT_STATUS = 0x03DA
MAXIMUM_SCAN_LINE = 0x09
LINE_OFFSET = 0x13

jmp start

updown DB 30
direction DB 0
filename DB "shoes.bmp",0

start:
; set mode 320x200 256 colors palette
        mov ah,0x0
        mov al,13h
        int 10h

; clear screen routine, not really needed
clearscreen:
        push ax
        mov ax, 0a000h
        mov es, ax
        pop ax
        xor di, di
        inc ax
        mov cx, 64000 ; 320x200
        rep stosb

; call file loader
        call Loadfile

        push cs
        pop ds

; after displaying the image or displaying an error, wait for keypress to exit
waitforkeyloop:
        call effect     ; Calling the effect
        MOV AH,1
        INT 16h
        JZ waitforkeyloop
        XOR AH,AH
        INT 16h
Exit:
        MOV AX,3        ; default text mode 3
        INT 10h
        MOV AX,4C00h    ; exit to dos (terminate process)
        INT 21h

Loadfile:
        MOV DX,filename
        MOV AX,3D00h    ; open filehandle
        INT 21h
        JC Err1
        MOV BX,AX       ; filehandle
        MOV CX,0FFFFh   ; size
        mov dx,0a000h   ; destination 0000:a000h - Screen memory
        mov ds,dx

        MOV DX,0
        MOV AH,3Fh      ; read from file
        INT 21h
        JC  Err1
        MOV AH,3Eh      ; close filehandle
        INT 21h

        RET
; print error
Err1:
        push cs         ; make ds same as cs
        pop ds
        MOV DX,TxtErr1  ; error
        MOV AH,09h
        INT 21h
        RET

effect:
        cli             ; stop interrupts
        call waitvretrace       ; wait for vertical retrace
        mov al, 0    ; set color index 0 to black (needs to be converted to a function
        mov dx, 3c8h
        out dx, al
        inc dx       ; now 3c9h
        mov al, 0h
        out dx, al   ; set R = 0
        mov al, 0h
        out dx, al   ; set G = 0
        mov al, 0h
        out dx, al   ; set B = 0

; gets start scanline and direction
        mov al,[updown]
        mov ah,[direction]
        cmp ah,0
        jz      addcounter
        dec al
        cmp al,30
        jnz gohere
        mov ah,0
        mov [direction],ah
        jmp gohere
addcounter:
        inc al
        cmp al,100
        jnz gohere
        mov ah,1
        mov [direction],ah
gohere:
        mov [updown],al

; al = scanline, call wait for scanline
        call waithretrace
        mov al, 0    ; set color index 0 to blueish
        mov dx, 3c8h
        out dx, al
        inc dx
        mov al, 11h
        out dx, al
        mov al, 22h
        out dx, al
        mov al, 33h
        out dx, al
; wait 10 scanlines (height of bar)
        mov al,10
        call waithretrace

; draw black again
        mov al, 0    ; set color index 0's rgb value
        mov dx, 3c8h
        out dx, al
        inc dx       ; now 3c9h
        mov al, 0
        out dx, al   ; set R = 11h
        mov al, 0h
        out dx, al   ; set G = 22h
        mov al, 0h
        out dx, al   ; set B = 33h

        sti     ; start interrupts again
        ret

; this waits for vertical retrace
waitvretrace:
        mov dx,INPUT_STATUS
waitv1:
        in al,dx
        test al,8
        jnz waitv1
waitv2:
        in al,dx
        test al,8
        jz waitv2
        ret

; routine that waits for horizontal retrace
waithretrace:
        mov cl,al
        mov dx,INPUT_STATUS
waith1:
        in al,dx
        test al,1
        jnz waith1
waith2:
        in al,dx
        test al,1
        jz waith2
        dec cl
        cmp cl,0
        jnz waith1
        ret

TxtErr1 DB "shoes.bmp not found!",7,10,13,"$"