PUBLIC _enableUnchainedVGAMode
PUBLIC _enableTextMode
PUBLIC _fillScreen
PUBLIC _latchCopyCube

DISPLAY_MODE_VGA equ 13h
DISPLAY_MODE_TEXT equ 03h

VGA_SEQUENCE_CONTROLLER_INDEX equ 0x3c4
VGA_SEQUENCE_CONTROLLER_DATA equ 0x3c5
VGA_SEQUENCE_CONTROLLER_MEMORY_MODE equ 0x04

VGA_SEQUENCE_CONTROLLER_MAP_MASK_MODE equ 0x02

VGA_GRAPHICS_MODE_INDEX equ 0x3CE
VGA_GRAPHICS_MODE equ 0x05

VGA_CRT_CONTROLLER_INDEX equ 0x03d4
VGA_CRT_CONTROLLER_DATA equ 0x03d5
VGA_CRT_CONTROLLER_UNDERLINE_LOC equ 0x14
VGA_CRT_CONTROLLER_MODE_CONTROL equ 0x17

.386
.model flat,c

.CODE

_enableUnchainedVGAMode:
  mov ax,0x0013;
  int 0x10

  mov dx, VGA_SEQUENCE_CONTROLLER_INDEX
  mov al, VGA_SEQUENCE_CONTROLLER_MEMORY_MODE
  mov ah, 0x06
  out dx, ax

  mov dx, VGA_CRT_CONTROLLER_INDEX
  mov al, VGA_CRT_CONTROLLER_MODE_CONTROL
  mov ah, 0xe3
  out dx, ax

  mov dx, VGA_CRT_CONTROLLER_INDEX
  mov al, VGA_CRT_CONTROLLER_UNDERLINE_LOC
  mov ah, 0x00
  out dx, ax

  ret

_enableTextMode:
  mov ah,0h
  mov al,DISPLAY_MODE_TEXT
  int 10h
  ret

_fillScreen:
  push ebp
  mov ebp, esp

  ; set all bitplanes
  mov dx, VGA_SEQUENCE_CONTROLLER_INDEX
  mov al, 0x02
  mov ah, 0fh
  out dx, ax

  mov al, [ebp+8] ; requested color

  mov cx, 16000 ; loop index
  mov ebx, 0xa0000
_fillScreen_loop:
  mov BYTE PTR [ebx], al
  inc ebx
  loop _fillScreen_loop

  mov esp,ebp
  pop ebp

  ret

_latchCopyCube:
  push ebp
  mov ebp,esp
  ; we need a y variable
  sub esp,4 ; y

  ; enable latch reads
  mov dx, VGA_SEQUENCE_CONTROLLER_INDEX
  mov al, VGA_SEQUENCE_CONTROLLER_MAP_MASK_MODE
  mov ah, 0xf
  out dx, ax

  mov dx, VGA_GRAPHICS_MODE_INDEX
  mov al, 0x08
  mov ah, 0x00
  out dx, ax

  mov DWORD PTR [ebp-4],16
  ; read across the cube, should take 4 * 16 reads
  mov cx,[ebp-4]
_latchCopyCube_yLoop:
  mov [ebp-4],cx ; put y back in loop

  mov eax,[ebp-4] ; put y in eax
  dec eax ; offset by 1 for loop
  ; can only multiply in eax by register
  mov bl,80
  mul bl ; number of lines
  add eax,0xa0000 ; vga base address

  ; start x loop
  mov cx,4
_latchCopyCube_xLoop:
  ; fill latches via memory read
  mov bl, BYTE PTR [eax]

  ; write blank
  mov [eax+12],0

  ; increment vga pointer
  inc eax

  ; loop until x is 0
  loop _latchCopyCube_xLoop

  ; restore y for looping
  mov cx,[ebp-4]

  ; loop until y is 0
  loop _latchCopyCube_yLoop

  ; put things back
  mov esp,ebp
  pop ebp
  ret

end