I don't know

; MAIN.ASM
bits 16
jmp kernel_main
%include "screen.asm"
kernel_main:
	cli
	; Code goes here
	
	call set_video_mode
	
	mov dl, 0x03
	call fill_screen
  
	mov bx, 0x02
	mov ch, 0x04
	mov dh, 'X'
	mov dl, 0x0f
	call print_char
	
	jmp $
	

; SCREEN.ASM
%define VGA_SEG 0xa000
%define VGA_MODE13_WIDTH 320
%define VGA_MODE13_HEIGHT 200

; Set video mode 0x13
set_video_mode:
	mov ah, 0x00				; Service #0
	mov al, 0x13				; Mode 0x13
	int 0x10					; Trigger the BIOS interrupt
	ret

; Plot from AX - x, BX - y
; DL register - color
plot:
	push dx
	push cx
	push bx
	push ax
	
	mov [0x7e00], dl 			; Temporarily store the pixel value in RAM
	
	mov cx, ax					; Make a backup of AX to be used to set the base VRAM address
	mov ax, 0xa000				; Store 0xA000 in the ES register
	mov es, ax					
	mov ax, bx					; Get the Y value
	mov dx, VGA_MODE13_WIDTH	; Multiply it by width (according to pos = y * width + x)
	mul dx
	add ax, cx					; and add the X to it
	mov bx, ax
	
	mov dl, [0x7e00]			; and restore it.
	
	; Now we got the offset, let's draw the pixel
	mov [es:bx], dl
	pop ax
	pop bx
	pop cx
	pop dx
	ret

; Fills the screen with pixel from AL
fill_screen:
	mov ax, VGA_MODE13_WIDTH
	mov bx, VGA_MODE13_HEIGHT
	fill_screen_a:
		fill_screen_b:	
			call plot
			dec ax
			cmp ax, 0xffff
			jne fill_screen_b
		mov ax, VGA_MODE13_WIDTH
		dec bx
		cmp bx, 0xffff
		jne fill_screen_a
	ret
%include "font.asm"
%include "text.asm"

; FONT.ASM
ascii_font:
	db 0x00, 0x00, 0x00, 0x00, 0x00
	db 0x3E, 0x5B, 0x4F, 0x5B, 0x3E
	db 0x3E, 0x6B, 0x4F, 0x6B, 0x3E
	db 0x1C, 0x3E, 0x7C, 0x3E, 0x1C
	db 0x18, 0x3C, 0x7E, 0x3C, 0x18
  ......
  db 0x00, 0x00, 0x00, 0x00, 0x00

; TEXT.ASM  
%define CHARACTER_WIDTH 	5
%define CHARACTER_HEIGHT 	7

plot_internal_pc:
	push dx
	push cx
	push bx
	push ax
	
	mov ax, bx
	mov bh, 0x00
	mov bl, ch
	;add bl, cls
	mov dl, 0x07
	call plot
	
	pop ax
	pop bx
	pop cx
	pop dx
	ret
	
do_column:
	; let's just do it hard coded this time
	; it's gonna be a hassle but alright
	
	mov [0x7e40], dl
	and dl, 0x80
	cmp dl, 0x00
	je dont_do_pix7
	mov cl, 0x07
	call plot_internal_pc
	dont_do_pix7:
	mov dl, [0x7e40]
	and dl, 0x40
	cmp dl, 0x00
	je dont_do_pix6
	mov cl, 0x06
	call plot_internal_pc
	dont_do_pix6:
	mov dl, [0x7e40]
	and dl, 0x20
	cmp dl, 0x00
	je dont_do_pix5
	mov cl, 0x05
	call plot_internal_pc
	dont_do_pix5:
	mov dl, [0x7e40]
	and dl, 0x10
	cmp dl, 0x00
	je dont_do_pix4
	mov cl, 0x04
	call plot_internal_pc
	dont_do_pix4:
	mov dl, [0x7e40]
	and dl, 0x08
	cmp dl, 0x00
	je dont_do_pix3
	mov cl, 0x03
	call plot_internal_pc
	dont_do_pix3:
	mov dl, [0x7e40]
	and dl, 0x04
	cmp dl, 0x00
	je dont_do_pix2
	mov cl, 0x02
	call plot_internal_pc
	dont_do_pix2:
	mov dl, [0x7e40]
	and dl, 0x02
	cmp dl, 0x00
	je dont_do_pix1
	mov cl, 0x01
	call plot_internal_pc
	dont_do_pix1:
	mov dl, [0x7e40]
	and dl, 0x01
	cmp dl, 0x00
	je dont_do_pix0
	mov cl, 0x00
	call plot_internal_pc
	dont_do_pix0:
	mov dl, [0x7e40]
	ret

; -------------------------------------
; Prints a character from DH register.
; Internal! AX - character addressing

; BX - x position
; CH - y position
; DH - input char
print_char:
	push dx
	push cx
	push bx
	push ax
	
	mov al, dh
	mov cl, 0x05
	mul cl
	mov cl, 0x04
	
	mov bx, ax
	
	loop1:
		push bx
		add bl, cl
		mov dl, [ascii_font + bx]
		pop bx
		
		call do_column
		
		dec cl
		cmp cl, 0x00
		jne loop1
	
	pop ax
	pop bx
	pop cx
	pop dx
	ret