format binary
use32
org 0x100000

MB_HEADER_MAGIC      equ 0x1BADB002
MB_PAGE_ALIGN        equ (1 shl 0)
MB_MEMORY_INFO       equ (1 shl 1)
MB_VIDEO_REQUEST     equ (1 shl 2)
MB_AOUT_KLUDGE       equ (1 shl 16)
MB_HEADER_FLAGS      equ MB_PAGE_ALIGN or MB_MEMORY_INFO or MB_VIDEO_REQUEST
MB_HEADER_FLAGS      equ MB_PAGE_ALIGN or MB_MEMORY_INFO or MB_VIDEO_REQUEST or MB_AOUT_KLUDGE
MB_CHECKSUM          equ -(MB_HEADER_MAGIC + MB_HEADER_FLAGS)

;; safe modes according to https://wiki.osdev.org/VESA_Video_Modes
VWIDTH  equ 640 ; 640/720
VHEIGHT equ 480 ; 480
VDEPTH  equ 32  ; 24/32

multiboot:
	dd MB_HEADER_MAGIC
	dd MB_HEADER_FLAGS
	dd MB_CHECKSUM
	dd multiboot	; header address
	dd 0x100000	; load address
	dd bss_start	; load end address
	dd bss_end	; bss end address
	dd start	; entry address

	dd 0	; video mode_type (0:fb, 1:txt) (set flags[2]!)
	dd VWIDTH	; video width
	dd VHEIGHT	; video height
	dd VDEPTH	; video depth

start:
	; Setup stack
	mov ebp, stack_top
	mov esp, stack_top

	;push ebx ; mboot info struct addr
	;push eax ; 0x2BADB002

	;mov [mbootmagic], eax
	;mov [mbootaddr], ebx

	; store video info
	mov ecx, [ebx+88]
	mov [fb.addr], ecx
	mov ecx, [ebx+98]
	mov [fb.pitch], ecx
	mov ecx, [ebx+100]
	mov [fb.width], ecx
	mov ecx, [ebx+104]
	mov [fb.height], ecx
	mov cl, [ebx+108]
	mov [fb.depth], cl

	; calculate bytespp
	movzx eax, cl
	mov cl, 8
	div byte cl
	mov [fb.bytespp], al

	; color component positions
	mov cl, [ebx+110+2]
	mov [fb.rpos], cl
	;mov cl, [ebx+111]
	;mov [fb.rmasksize], cl
	mov cl, [ebx+112+2]
	mov [fb.gpos], cl
	;mov cl, [ebx+113]
	;mov [fb.gmasksize], cl
	mov cl, [ebx+114+2]
	mov [fb.bpos], cl
	;mov cl, [ebx+115]
	;mov [fb.bmasksize], cl
testpixels:
	; construct pixel R
	mov al, 0xff ;r
	mov ah, 0x00 ;g
	mov ch, 0x00 ;b
	xor edx, edx ;final pixel
	;ebx is temp pixel
	movzx ebx, al
	mov cl, [fb.rpos]
	shl ebx, cl
	;and ebx, [fb.rmasksize]
	or edx, ebx
	movzx ebx, ah
	mov cl, [fb.gpos]
	shl ebx, cl
	;and ebx, [fb.gmasksize]
	or edx, ebx
	movzx ebx, ch
	mov cl, [fb.bpos]
	shl ebx, cl
	;and ebx, [fb.bmasksize]
	or edx, ebx
	mov ecx, [fb.addr]
	mov [ecx], edx

	; construct pixel G
	mov al, 0x00 ;r
	mov ah, 0xff ;g
	mov ch, 0x00 ;b
	xor edx, edx ;final pixel
	;ebx is temp pixel
	movzx ebx, al
	mov cl, [fb.rpos]
	shl ebx, cl
	;and ebx, [fb.rmasksize]
	or edx, ebx
	movzx ebx, ah
	mov cl, [fb.gpos]
	shl ebx, cl
	;and ebx, [fb.gmasksize]
	or edx, ebx
	movzx ebx, ch
	mov cl, [fb.bpos]
	shl ebx, cl
	;and ebx, [fb.bmasksize]
	or edx, ebx
	mov ecx, [fb.addr]
	movzx ebx, [fb.bytespp]
	add ecx, ebx
	mov [ecx], edx

	; construct pixel B
	mov al, 0x00 ;r
	mov ah, 0x00 ;g
	mov ch, 0xff ;b
	xor edx, edx ;final pixel
	;ebx is temp pixel
	movzx ebx, al
	mov cl, [fb.rpos]
	shl ebx, cl
	;and ebx, [fb.rmasksize]
	or edx, ebx
	movzx ebx, ah
	mov cl, [fb.gpos]
	shl ebx, cl
	;and ebx, [fb.gmasksize]
	or edx, ebx
	movzx ebx, ch
	mov cl, [fb.bpos]
	shl ebx, cl
	;and ebx, [fb.bmasksize]
	or edx, ebx
	mov ecx, [fb.addr]
	movzx ebx, [fb.bytespp]
	add ecx, ebx
	add ecx, ebx
	mov [ecx], edx

	;mov dword [edx], 0xff00ff00
testpixels_end:

hang:
	;cli
	.loop:
		;hlt
		jmp .loop
error:
	mov dword [0xFD000000], 0x00FF0000
	jmp hang

mbootaddr: dd 0
mbootmagic: dd 0
fb:
	.addr dd 0
	.pitch dd 0
	.width dd 0
	.height dd 0
	.depth db 0
	.bytespp db 0
	.rpos db 0
	;.rmasksize db 0
	.gpos db 0
	;.gmasksize db 0
	.bpos db 0
	;.bmasksize db 0

align 4096
bss_start:
align 4096
stack_bottom:
rb 16384
stack_top:
bss_end: