===========================================================================
 BBS: The Abacus * HST/DS * Potterville, MI
Date: 06-08-93 (03:04)             Number: 202
From: RICH GELDREICH               Refer#: NONE
  To: CALVIN FRENCH                 Recvd: NO  
Subj: Gif Loader/2                   Conf: (35) Quick Basi
---------------------------------------------------------------------------
'>>> Start of page 2.

    LOOP WHILE A = 0           'loop while byte fetched is zero

    SELECT CASE A
    CASE 44  'We've found an image descriptor!
        EXIT DO
    CASE 59  'GIF trailer, stop decoding.
        GOTO AllDone
    CASE IS <> 33
        PRINT "Unknown GIF extension type.": END
    END SELECT
    'Skip by blocked extension data.
    GOSUB GetByte
    DO: GOSUB GetByte: A$ = SPACE$(A): GET #1, , A$: LOOP UNTIL_
 A = 0
LOOP
'Get image's start coordinates and size.
GET #1, , XStart: GET #1, , YStart: GET #1, , XLength: GET #1, ,_
 YLength
XEnd = XStart + XLength: YEnd = YStart + YLength

'Check for local colormap, and fetch it if it exists.
GOSUB GetByte
IF (A AND 128) THEN
    NoPalette = 0
    NumColors = 2 ^ ((A AND 7) + 1)
    P$ = SPACE$(NumColors * 3): GET #1, , P$
END IF

'Check for interlaced image.
Interlaced = (A AND 64) > 0: PassNumber = 0: PassStep = 8

'Get LZW starting code size.
GOSUB GetByte

'Calculate clear code, end of stream code, and first free LZW code.
ClearCode = 2 ^ A
EOSCode = ClearCode + 1
FirstCode = ClearCode + 2: NextCode = FirstCode
StartCodeSize = A + 1: CodeSize = StartCodeSize

'Find maximum code for the current code size.
StartMaxCode = 2 ^ (A + 1) - 1: MaxCode = StartMaxCode

BitsIn = 0: BlockSize = 0: BlockPointer = 1

X = XStart: y = YStart: YBase = y * 320&

'Set screen 13 in not set yet.
IF FirstTime = 0 THEN
    'Go to VGA mode 13 (320x200x256).
    SCREEN 13: DEF SEG = &HA000
END IF

'Set palette, if there was one.
IF NoPalette = 0 THEN
    'Use OUTs for speed.
    OUT &H3C8, 0
    FOR A = 1 TO NumColors * 3: OUT &H3C9, ASC(MID$(P$, A, 1)) \_
 4: NEXT
    'Save palette of image to disk.
    'OPEN "pal." FOR BINARY AS #2: PUT #2, , P$: CLOSE #2
END IF

IF FirstTime = 0 THEN
  'Clear entire screen to background color. This isn't
  'done until the image's palette is set, to avoid flicker
  'on some GIFs.
    LINE (0, 0)-(319, 199), Background, BF
    FirstTime = -1
END IF

'Decode LZW data stream to screen.
DO
    'Retrieve one LZW code.
    GOSUB GetCode
    'Is it an end of stream code?
    IF Code <> EOSCode THEN
        'Is it a clear code? (The clear code resets the sliding
        'dictionary - it *should* be the first LZW code present
' in
        'the data stream.)

'>>> Continued on page 3

--- MsgToss 2.0b
 * Origin: Computer Co-Op - Voorhees, NJ | Ted Hare (1:266/29)
SEEN-BY: 1/211 11/2 4 13/13 101/1 108/89 109/25 110/69 114/5 123/19 124/1
SEEN-BY: 153/752 154/40 77 157/110 159/100 125 430 575 950 203/23 209/209
SEEN-BY: 261/1023 280/1 390/1 396/1 15 397/2 2230/100 2440/5 3603/20