dosg.asm

	[bits 16]
	
	org 0x100
main:
	mov ah, 0x0f
	int 0x10     ; get video mode
	push ax     ; store vid mode
	
	mov ah, 0x00
	mov al, 0x13
	int 0x10     ; set to graphics mode
	
.j:
	push word 65535
	push word 10
	push word 0
	push word 0
	push word 0xf
	call renderint
	jmp .j
	
	pop ax      ; restore vid mode
	mov ah, 0x00
	int 0x10
	
	mov ah, 0x4c
	int 0x21 ; exit
	
; Blits a texture onto the screen
;
; width  12[bp]
; height 10[bp]
; xoffs   8[bp]
; yoffs   6[bp]
; tex     4[bp]
rendertex:
	push bp
	mov bp, sp
	
	mov ax, 0xa000
	mov es, ax
	
	mov cx, 0 ; cx = y
.jmpY:
	cmp cx, [bp + 10]
	jge .breakY
	
	mov di, 0 ; di = x
.jmpX:
	mov ax, [bp + 12]
	cmp di, ax
	jge .breakX
	
	mul cx
	add ax, di        ; (y * width) + x
	mov bx, ax
	mov si, [bp + 4] 
	mov bl, [si + bx] ; bl = tex[y * width + x]
	
	mov ax, [bp + 6]
	add ax, cx
	mov si, 320
	mul si          ; (yoffs + y) * 320
	add ax, [bp + 8]
	add ax, di      ; + xoffs + x
	mov si, ax
	mov [es:si], bl
	
	inc di
	jmp .jmpX
.breakX:
	inc cx
	jmp .jmpY
.breakY:
	
	pop bp
	retn 10

; Writes an int to the screen
;
; i     12[bp]
; base  10[bp]
; xoffs  8[bp]
; yoffs  6[bp]
; col    4[bp]
renderint:
	push bp
	mov bp, sp
	
	mov cx, 0
	mov ax, [bp + 12]
.calcloop:
	cmp ax, 0
	je .leave         ; if (!i) break
	
	xor dx,dx
	div word [bp + 10] ; i /= base, dx has remainder
	push dx ; store rem on stack
	inc cx ; inc digit count
	jmp .calcloop
.leave:
	push cx     ;numDigits
	push word 0 ;numDigit
.renderloop:
	;render digits in reverse order
	
	pop di ;numDigit
	pop cx ;numDigits
	cmp di, cx
	jge .return
	
	pop bx ;pop the previously pushed remainder (digit) (first arg)
	
	push cx
	push di ;save numDigit, numDigits
	
	push bx ;digit, first arg
	mov ax, 5 
	mul di
	add ax, [bp + 8]
	push ax            ;xoffsnew = xoffs + 5*numDigit
	push word [bp + 6] ;yoffs
	
	push word [bp + 4] ;col
	call renderdigit
	
	pop bx
	inc bx
	push bx ;++numDigit (numDigit is at top of stack)
	
	jmp .renderloop
	
.return:
	pop bp
	retn 10

; dl contains colour
; si contains tex
replcol:
	push bx
	
	mov bx, -1
.rcolloop:
	inc bx
	cmp bx, 20 ;4*5
	jge .breakcolloop
	cmp [si + bx], byte 0
	je .rcolloop
	mov [si + bx], dl
	jmp .rcolloop
	
.breakcolloop:
	pop bx
	
	retn
	
; Write digit to the screen
;
; digit 10[bp]
; xoffs  8[bp]
; yoffs  6[bp]
; col    4[bp]
renderdigit:
	push bp
	mov bp, sp
	
	mov ax, 2
	mul word [bp + 10]
	mov bx, ax
	mov si, [texnummap + bx]
	
	mov dl, [bp + 4] ; little endian, col byte is the first one
	call replcol     ; replace colours with col
	
	push word 4 ;w
	push word 5 ;h
	push word [bp + 8] ;xoffs
	push word [bp + 6] ;yoffs
	
	push word si  ;tex
	call rendertex
	
	pop bp
	retn 8

	tex0 db 0,1,1,0, 1,0,0,1, 1,0,0,1, 1,0,0,1, 0,1,1,0
	tex1 db 0,0,1,0, 0,0,1,0, 0,0,1,0, 0,0,1,0, 0,0,1,0
	tex2 db 0,1,1,0, 1,0,0,1, 0,0,1,0, 0,1,0,0, 1,1,1,1
	tex3 db 1,1,1,0, 0,0,0,1, 0,1,1,0, 0,0,0,1, 1,1,1,0
	tex4 db 1,0,0,1, 1,0,0,1, 1,1,1,1, 0,0,0,1, 0,0,0,1
	tex5 db 1,1,1,1, 1,0,0,0, 1,1,1,0, 0,0,0,1, 1,1,1,0
	tex6 db 0,1,1,1, 1,0,0,0, 1,1,1,1, 1,0,0,1, 1,1,1,1
	tex7 db 1,1,1,1, 0,0,0,1, 0,0,1,0, 0,1,0,0, 1,0,0,0
	tex8 db 0,1,1,0, 1,0,0,1, 0,1,1,0, 1,0,0,1, 0,1,1,0
	tex9 db 0,1,1,0, 1,0,0,1, 0,1,1,0, 0,0,0,1, 1,1,1,0
	texA db 0,1,1,0, 1,0,0,1, 1,1,1,1, 1,0,0,1, 1,0,0,1
	texB db 1,1,1,0, 1,0,0,1, 1,1,1,1, 1,0,0,1, 1,1,1,1
	texC db 0,1,1,1, 1,0,0,0, 1,0,0,0, 1,0,0,0, 0,1,1,1
	texD db 1,1,1,0, 1,0,0,1, 1,0,0,1, 1,0,0,1, 1,1,1,1
	texE db 1,1,1,1, 1,0,0,0, 1,1,1,0, 1,0,0,0, 1,1,1,1
	texF db 1,1,1,1, 1,0,0,0, 1,1,1,0, 1,0,0,0, 1,0,0,0
	texnummap dw tex0,tex1,tex2,tex3,tex4,tex5,tex6,tex7,tex8,tex9,texA,texB,texC,texD,texE,texF