"

 COPYRIGHT (c) 1991 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

ImageReader subclass:#GIFReader

	instanceVariableNames:'redMap greenMap blueMap'

	classVariableNames:''

	poolDictionaries:''

	category:'Graphics-Images support'

!

!GIFReader class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1991 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

!

documentation

"

    this class provides methods for loading and saving GIF pictures.

    It has been tested with some different GIF87a pictures, I dont

    know, if it works with other GIF versions.

    GIF extension blocks are not handled.

    GIF file writing is not implemented (use TIFF).

    legal stuff extracted from GIF87a documentation:

    CompuServe Incorporated hereby grants a limited, non-exclusive, royalty-free

    license for the use of the Graphics Interchange Format(sm) in computer

    software; computer software utilizing GIF(sm) must acknowledge ownership of the

    Graphics Interchange Format and its Service Mark by CompuServe Incorporated, in

    User and Technical Documentation. 

      The Graphics Interchange Format(c) is the Copyright property of

      CompuServe Incorporated. GIF(sm) is a Service Mark property of

      CompuServe Incorporated.

    [See also:]

        Image Form Icon

        BlitImageReader FaceReader JPEGReader PBMReader PCXReader 

        ST80FormReader SunRasterReader TargaReader TIFFReader WindowsIconReader 

        XBMReader XPMReader XWDReader 

    [author:]

        Claus Gittinger

"

! !

!GIFReader class methodsFor:'initialization'!

initialize

    "install myself in the Image classes fileFormat table

     for the `.gif', and '.GIF' extensions."

    Image fileFormats at:'.gif'  put:self.

    Image fileFormats at:'.GIF'  put:self.

    "Modified: 23.4.1996 / 12:28:16 / cg"

! !

!GIFReader class methodsFor:'testing'!

isValidImageFile:aFileName

    "return true, if aFileName contains a GIF image"

    |id inStream|

    inStream := self streamReadingFile:aFileName.

    inStream isNil ifTrue:[^ false].

    id := String new:6.

    inStream nextBytes:6 into:id.

    inStream close.

    (id = 'GIF87a') ifFalse:[

        (id startsWith:'GIF') ifFalse:[^ false].

        id ~= 'GIF89a' ifTrue:[ 

            'GIFReader: not a GIF87a/GIF89a file - hope that works' infoPrintNL.

        ]

    ].

    ^ true

    "Modified: 7.3.1996 / 19:16:52 / cg"

! !

!GIFReader methodsFor:'reading from file'!

checkGreyscaleColormap

    |sz "{ Class: SmallInteger }"

     redVal|

    sz := redMap size.

    1 to:sz do:[:i |

    ].

    ^ true

!

fromStream:aStream

    "read a stream containing a GIF image.

     Leave image description in instance variables."

    |byte index flag count

     colorMapSize bitsPerPixel scrWidth scrHeight

     hasColorMap hasLocalColorMap interlaced id

     leftOffs topOffs codeLen

     compressedData compressedSize

     tmp srcOffset dstOffset isGif89

     h "{ Class: SmallInteger }"|

    inStream := aStream.

    aStream binary.

    "GIF-files are always lsb (intel-world)"

    byteOrder := #lsb.

    id := String new:6.

    aStream nextBytes:6 into:id.

    "all I had for testing where GIF87a files;

     I hope later versions work too ..."

    isGif89 := false.

    (id ~= 'GIF87a') ifTrue:[

        (id startsWith:'GIF') ifFalse:[

            'GIFReader: not a gif file' infoPrintNL.

            ^ nil

        ].

        id ~= 'GIF89a' ifTrue:[ 

            'GIFReader: not a GIF87a/GIF89a file - hope that works' infoPrintNL.

        ]

    ].

    "get screen dimensions (not used)"

    scrWidth := aStream nextShortMSB:false.

    scrHeight := aStream nextShortMSB:false.

    "get flag byte"

    flag := aStream nextByte.

    hasColorMap :=      (flag bitAnd:2r10000000) ~~ 0.

    "bitsPerRGB :=     ((flag bitAnd:2r01110000) bitShift:-4) + 1. "

    "colorMapSorted := ((flag bitAnd:2r00001000) ~~ 0.             "

    bitsPerPixel :=     (flag bitAnd:2r00000111) + 1.

    colorMapSize := 1 bitShift:bitsPerPixel.

    "get background (not used)"

    aStream nextByte.

    "aspect ratio (not used)"

    aStream nextByte.

    "get colorMap"

    hasColorMap ifTrue:[

        self readColorMap:colorMapSize

    ].

    "skip gif89a extensions "

    byte := aStream nextByte.

    [byte == 16r21] whileTrue:[

        "/ extension

        self readExtension:aStream.

        byte := aStream nextByte.

    ].

    "must now be image separator"

    (byte ~~ 16r2C) ifTrue:[

        ('GIFReader: corrupted gif file (no IMAGESEP): ' , (byte printStringRadix:16)) infoPrintNL.

        ^ nil

    ].

    "get image data"

    leftOffs := aStream nextShortMSB:false.

    topOffs := aStream nextShortMSB:false.

    width := aStream nextShortMSB:false.

    height := aStream nextShortMSB:false.

"

'width ' print. width printNewline.

'height ' print. height printNewline.

"

    "another flag byte"

    flag := aStream nextByte.

    interlaced :=           (flag bitAnd:2r01000000) ~~ 0.

    hasLocalColorMap :=     (flag bitAnd:2r10000000) ~~ 0.

    "localColorMapSorted := (flag bitAnd:2r00100000) ~~ 0.      "

    "if image has a local colormap, this one is used"

    hasLocalColorMap ifTrue:[

        "local descr. overwrites"

        bitsPerPixel := (flag bitAnd:2r00000111) + 1.

        colorMapSize := 1 bitShift:bitsPerPixel.

" 'local colormap' printNewline. "

        "overwrite colormap"

        self readColorMap:colorMapSize

    ].

    "get codelen for decompression"

    codeLen := aStream nextByte.

    compressedData := ByteArray uninitializedNew:(aStream size).

    "get compressed data"

    index := 1.

    count := aStream nextByte.

    [count notNil and:[count ~~ 0]] whileTrue:[

        aStream nextBytes:count into:compressedData startingAt:index.

        index := index + count.

        count := aStream nextByte

    ].

    compressedSize := index - 1.

    h := height.

    data := ByteArray new:((width + 1) * (h + 1)).

"/    'GIFReader: decompressing ...' infoPrintNL.

    self class decompressGIFFrom:compressedData

                           count:compressedSize

                            into:data

                      startingAt:1

                         codeLen:(codeLen + 1).

    interlaced ifTrue:[

        Transcript showCr:'deinterlacing'.

        tmp := ByteArray new:(data size).

        "phase 1: 0, 8, 16, 24, ..."

        srcOffset := 1.

        0 to:(h - 1) by:8 do:[:dstRow |

            dstOffset := dstRow * width + 1.

            tmp replaceFrom:dstOffset to:(dstOffset + width - 1)

                       with:data startingAt:srcOffset.

            srcOffset := srcOffset + width.

        ].

        "phase 2: 4, 12, 20, 28, ..."

        4 to:(h - 1) by:8 do:[:dstRow |

            dstOffset := dstRow * width + 1.

            tmp replaceFrom:dstOffset to:(dstOffset + width - 1)

                       with:data startingAt:srcOffset.

            srcOffset := srcOffset + width.

        ].

        "phase 3: 2, 6, 10, 14, ..."

        2 to:(h - 1) by:4 do:[:dstRow |

            dstOffset := dstRow * width + 1.

            tmp replaceFrom:dstOffset to:(dstOffset + width - 1)

                       with:data startingAt:srcOffset.

            srcOffset := srcOffset + width.

        ].

        "phase 4: 1, 3, 5, 7, ..."

        1 to:(h - 1) by:2 do:[:dstRow |

            dstOffset := dstRow * width + 1.

            tmp replaceFrom:dstOffset to:(dstOffset + width - 1)

                       with:data startingAt:srcOffset.

            srcOffset := srcOffset + width.

        ].

        data := tmp.

        tmp := nil

    ].

    photometric := #palette.

    samplesPerPixel := 1.

    bitsPerSample := #(8).

    "check if only grey values are used,

     could make it a greyscale image if so (currently not done)"

"/    self checkGreyscaleColormap ifTrue:[

"/        self makeGreyscale

"/    ].

    "

     GIFReader fromFile:'../fileIn/bitmaps/claus.gif

     GIFReader fromFile:'../fileIn/bitmaps/garfield.gif'

    "

!

makeGreyscale

    "not yet implemented/needed"

!

readColorMap:colorMapSize

    "get gif colormap consisting of colorMapSize entries"

    |sz "{ Class: SmallInteger }"|

    redMap := ByteArray uninitializedNew:colorMapSize.

    greenMap := ByteArray uninitializedNew:colorMapSize.

    blueMap := ByteArray uninitializedNew:colorMapSize.

    sz := colorMapSize.

    1 to:sz do:[:i |

    ]

!

readExtension:aStream

    |type blockSize subBlockSize

     aspNum aspDen left top width height cWidth cHeight fg bg|

    type := aStream nextByte.

    type == $R asciiValue ifTrue:[

        "/ Ratio extension

        'GIFREADER: ratio extension ignored' infoPrintNL.

        blockSize := aStream nextByte.

        (blockSize == 2) ifTrue:[

            aspNum := aStream nextByte.

            aspDen := aStream nextByte

        ] ifFalse:[

            aStream skip:blockSize

        ].

        "/ eat subblocks

        [(subBlockSize := aStream nextByte) > 0] whileTrue:[

            aStream skip:subBlockSize

    ]

! !

!GIFReader class methodsFor:'documentation'!

version

! !

GIFReader initialize!