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; GIF LITE v2.0 by Willow

; Written in pure assembler by Ivushkin Andrey aka Willow

;

; This include file will contain functions to handle GIF image format

;

; Created: August 15, 2004

; Last changed: September 9, 2004

; Change COLOR_ORDER in your program

; if colors are displayed improperly

if ~ (COLOR_ORDER in )

; This message may not appear under MenuetOS, so watch...

  display 'Please define COLOR_ORDER: MENUETOS or OTHER',13,10

end if

; virtual structure, used internally

struc GIF_list

{

    .NextImg rd 1

    .Left   rw 1

    .Top    rw 1

    .Width  rw 1

    .Height rw 1

}

struc GIF_info

{

    .Left   rw 1

    .Top    rw 1

    .Width  rw 1

    .Height rw 1

}

_null fix 0x1000

; ****************************************

;   FUNCTION ReadGIF - unpacks GIF image

; ****************************************

; in:

;   esi - pointer to GIF file in memory

;   edi - pointer to output image list

;   eax - pointer to work area (MIN 16 KB!)

; out:

;   eax - 0, all OK;

;   eax - 1, invalid signature;

;   eax >=8, unsupported image attributes

;

;   ecx - number of images

ReadGIF:

    push esi edi

    mov  [.table_ptr],eax

    mov  [.cur_info],edi

    xor  eax,eax

    mov  [.globalColor],eax

    mov  [.img_count],eax

    inc  eax

    cmp  dword[esi],'GIF8'

    jne  .er            ; signature

    mov  ecx,[esi+0xa]

    inc  eax

    add  esi,0xd

    mov  edi,esi

    bt   ecx,7

    jnc  .nextblock

    mov  [.globalColor],esi

    call .Gif_skipmap

  .nextblock:

    cmp  byte[edi],0x21

    jne  .noextblock

    inc  edi

    cmp  byte[edi],0xf9 ; Graphic Control Ext

    jne  .no_gc

    add  edi,7

    jmp  .nextblock

  .no_gc:

    cmp  byte[edi],0xfe ; Comment Ext

    jne  .no_comm

    inc  edi

  .block_skip:

    movzx eax,byte[edi]

    lea  edi,[edi+eax+1]

    cmp  byte[edi],0

    jnz  .block_skip

    inc  edi

    jmp  .nextblock

  .no_comm:

    cmp  byte[edi],0xff ; Application Ext

    jne  .nextblock

    add  edi,13

    jmp  .block_skip

  .noextblock:

    cmp  byte[edi],0x2c    ; image beginning

    jne  .er

    inc  [.img_count]

    inc  edi

    mov  esi,[.cur_info]

    add  esi,4

    xchg esi,edi

    movsd

    movsd

    push edi

    movzx ecx,word[esi]

    inc  esi

    bt   ecx,7

    jc   .uselocal

    push [.globalColor]

    mov  edi,esi

    jmp  .setPal

  .uselocal:

    call .Gif_skipmap

    push esi

  .setPal:

    movzx ecx,byte[edi]

    inc  ecx

    mov  [.codesize],ecx

    dec  ecx

    pop  [.Palette]

    lea  esi,[edi+1]

    mov  edi,[.table_ptr]

    xor  eax,eax

    cld

    lodsb               ; eax - block_count

    add  eax,esi

    mov  [.block_ofs],eax

    mov  [.bit_count],8

    mov  eax,1

    shl  eax,cl

    mov  [.CC],eax

    inc  eax

    mov  [.EOI],eax

    lea  ecx,[eax-1]

    mov  eax, _null shl 16

  .filltable:

    stosd

    inc  eax

    loop .filltable

    pop  edi

    mov  [.img_start],edi

  .reinit:

    mov  edx,[.EOI]

    inc  edx

    push [.codesize]

    pop  [.compsize]

    call .Gif_get_sym

    cmp  eax,[.CC]

    je   .reinit

    call .Gif_output

  .cycle:

    movzx ebx,ax

    call .Gif_get_sym

    cmp  eax,edx

    jae  .notintable

    cmp  eax,[.CC]

    je   .reinit

    cmp  eax,[.EOI]

    je   .end

    call .Gif_output

  .add:

    push eax

    mov  eax,[.table_ptr]

    mov  [eax+edx*4],ebx

    pop  eax

    cmp  edx,0xFFF

    jae  .cycle

    inc  edx

    bsr  ebx,edx

    cmp  ebx,[.compsize]

    jne  .noinc

    inc  [.compsize]

  .noinc:

    jmp  .cycle

  .notintable:

    push eax

    mov  eax,ebx

    call .Gif_output

    push ebx

    movzx eax,bx

    call .Gif_output

    pop  ebx eax

    jmp  .add

  .er:

    pop  edi

    jmp  .ex

  .end:

    mov  eax,[.cur_info]

    mov  [eax],edi

    mov  [.cur_info],edi

    add  esi,2

    xchg esi,edi

  .nxt:

    cmp  byte[edi],0

    jnz  .continue

    inc  edi

    jmp  .nxt

  .continue:

    cmp  byte[edi],0x3b

    jne  .nextblock

    xor  eax,eax

    stosd

    mov  ecx,[.img_count]

  .ex:

    pop  edi esi

    ret

.Gif_skipmap:

; in: ecx - image descriptor, esi - pointer to colormap

; out: edi - pointer to area after colormap

    and  ecx,111b

    inc  ecx            ; color map size

    mov  ebx,1

    shl  ebx,cl

    lea  ebx,[ebx*2+ebx]

    lea  edi,[esi+ebx]

    ret

.Gif_get_sym:

    mov  ecx,[.compsize]

    push ecx

    xor  eax,eax

  .shift:

    ror  byte[esi],1

    rcr  eax,1

    dec  [.bit_count]

    jnz  .loop1

    inc  esi

    cmp  esi,[.block_ofs]

    jb   .noblock

    push eax

    xor  eax,eax

    lodsb

    test eax,eax

    jnz  .nextbl

    mov  eax,[.EOI]

    sub  esi,2

    add  esp,8

    jmp  .exx

  .nextbl:

    add  eax,esi

    mov  [.block_ofs],eax

    pop  eax

  .noblock:

    mov  [.bit_count],8

  .loop1:

    loop .shift

    pop  ecx

    rol  eax,cl

  .exx:

    xor  ecx,ecx

    ret

.Gif_output:

    push esi eax edx

    mov  edx,[.table_ptr]

  .next:

    push word[edx+eax*4]

    mov  ax,word[edx+eax*4+2]

    inc  ecx

    cmp  ax,_null

    jnz  .next

    shl  ebx,16

    mov  bx,[esp]

  .loop2:

    pop  ax

    lea  esi,[eax+eax*2]

    add  esi,[.Palette]

    if COLOR_ORDER eq MENUETOS

        mov  esi,[esi]

        bswap esi

        shr  esi,8

        mov  [edi],esi

        add  edi,3

    else

    		movsw

        movsb

        and  byte[edi],0

        inc  edi

    end if

    loop .loop2

    pop  edx eax esi

    ret

    .globalColor rd 1

    .img_count rd 1

    .cur_info rd 1        ; image table pointer

    .img_start rd 1

    .codesize rd 1

    .compsize rd 1

    .bit_count rd 1

    .CC rd 1

    .EOI rd 1

    .Palette rd 1

    .block_ofs rd 1

    .table_ptr rd 1