===========================================================================
 BBS: The Abacus * HST/DS * Potterville, MI
Date: 06-08-93 (03:05)             Number: 203
From: RICH GELDREICH               Refer#: NONE
  To: CALVIN FRENCH                 Recvd: NO  
Subj: Gif Loader/3                   Conf: (35) Quick Basi
---------------------------------------------------------------------------
'>>> Start of page 3.

        IF Code = ClearCode THEN
            NextCode = FirstCode
            CodeSize = StartCodeSize
            MaxCode = StartMaxCode
            GOSUB GetCode
            CurCode = Code: LastCode = Code: LastPixel = Code
            IF X < 320 AND y < 200 THEN POKE X + YBase, LastPixel
            X = X + 1: IF X = XEnd THEN GOSUB NextScanLine
        ELSE
            CurCode = Code: StackPointer = 0

            'Have we entered this code into the dictionary yet?
            IF Code >= NextCode THEN
                IF Code > NextCode THEN GOTO AllDone 'Bad GIF if
' this happens.
               'mimick last code if we haven't entered the
' requested
               'code into the dictionary yet
                CurCode = LastCode
                OutStack(StackPointer) = LastPixel
                StackPointer = StackPointer + 1
            END IF

            'Recursively get each character of the string.
            'Since we get the characters in reverse, "push" them
            'onto a stack so we can "pop" them off later.
            'Hint: There is another, much faster way to
' accomplish
            'this that doesn't involve a decoding stack at all...
            DO WHILE CurCode >= FirstCode
                OutStack(StackPointer) = Suffix(CurCode)
                StackPointer = StackPointer + 1
                CurCode = Prefix(CurCode)
            LOOP

            LastPixel = CurCode
            IF X < 320 AND y < 200 THEN POKE X + YBase, LastPixel
            X = X + 1: IF X = XEnd THEN GOSUB NextScanLine

            '"Pop" each character onto the display.
            FOR A = StackPointer - 1 TO 0 STEP -1
                IF X < 320 AND y < 200 THEN POKE X + YBase,_
 OutStack(A)
                X = X + 1: IF X = XEnd THEN GOSUB NextScanLine
            NEXT

            'Can we put this new string into our dictionary?
' (Some GIF
            'encoders will wait a bit when the dictionary is full
            'before sending a clear code- this increases
' compression
            'because the dictionary's contents are thrown away
' less
            'often.)
            IF NextCode < 4096 THEN
                'Store new string in the dictionary for later
' use.
                Prefix(NextCode) = LastCode
                Suffix(NextCode) = LastPixel
                NextCode = NextCode + 1
                'Time to increase the LZW code size?
                IF (NextCode > MaxCode) AND (CodeSize < 12) THEN
                    CodeSize = CodeSize + 1
                    MaxCode = MaxCode * 2 + 1
                END IF
            END IF
            LastCode = Code
        END IF
    END IF
LOOP UNTIL Code = EOSCode

LOOP

AllDone:

'Save image and palette to BSAVE file.
'DEF SEG = &HA000
'OUT &H3C7, 0
'FOR a = 0 TO 767
'    POKE a + 64000, INP(&HÃ9)
'NEXT

'>>> Continued on page 4

--- MsgToss 2.0b
 * Origin: Computer Co-Op - Voorhees, NJ | Ted Hare (1:266/29)
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