"

 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

	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' extensions."

    MIMETypes defineImageType:'image/gif' suffix:'gif' reader:self.

    "Modified: 1.2.1997 / 14:59:37 / 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].

    inStream text.

    id := String new:6.

    inStream nextBytes:6 into:id.

    inStream close.

    (id = 'GIF87a') ifFalse:[

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

        id ~= 'GIF89a' ifTrue:[ 

            'GIFReader [info]: not a GIF87a/GIF89a file - hope that works' infoPrintCR.

        ]

    ].

    ^ true

    "Modified: 10.1.1997 / 15:40:34 / cg"

! !

!GIFReader methodsFor:'reading from file'!

checkGreyscaleColormap

    "return true, if colormap is actually a greymap.

     Could be used to convert it into a greyScale image - which is not yet done."

    |sz "{ Class: SmallInteger }"

     redVal|

    sz := redMap size.

    1 to:sz do:[:i |

        redVal := redMap at:i.

        redVal ~~ (greenMap at:i) ifTrue:[^ false].

        redVal ~~ (blueMap at:i) ifTrue:[^ false].

    ].

    ^ true

    "Modified: 2.5.1996 / 17:54:40 / cg"

!

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 atEnd

     h "{ Class: SmallInteger }"|

    inStream := aStream.

    aStream binary.

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

    byteOrder := #lsb.

    id := ByteArray new:6.

    aStream nextBytes:6 into:id startingAt:1.

    id := id asString.

    "all I had for testing where GIF87a files;

     I hope later versions work too ..."

    isGif89 := false.

    (id ~= 'GIF87a') ifTrue:[

        (id startsWith:'GIF') ifFalse:[

            'GIFReader [info]: not a gif file' infoPrintCR.

            ^ nil

        ].

        id ~= 'GIF89a' ifTrue:[ 

            'GIFReader [info]: not a GIF87a/GIF89a file - hope that works' infoPrintCR.

        ]

    ].

    "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.

        colorMap := Colormap 

                        redVector:redMap 

                        greenVector:greenMap 

                        blueVector:blueMap.

    ].

    photometric := #palette.

    samplesPerPixel := 1.

    bitsPerSample := #(8).

    atEnd := false.

    [atEnd] whileFalse:[

        "gif89a extensions"

        byte := aStream nextByte.

            "/ extension

            self readExtension:aStream.

"/

"/

                ].

                imageSequence isNil ifTrue:[

                    imageSequence := OrderedCollection new.

                ].

                    "/

                    "/ ok, there is a maskValue

                    "/ build a Depth1Image for it.

                    "/

                ].

                imageSequence add:(self image).

                aStream atEnd ifTrue:[

                    atEnd := true.

                ]

            ]

        ].

    ].

    "

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

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

     GIFReader new fromStream:('/home2/cg/.misc/circum.gif' asFilename readStream)

    "

    "Modified: 5.7.1996 / 17:32:01 / stefan"

!

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 |

        redMap at:i put:(inStream nextByte).

        greenMap at:i put:(inStream nextByte).

        blueMap at:i put:(inStream nextByte)

    ].

    "Modified: 21.6.1996 / 12:32:43 / cg"

!

readExtension:aStream

    "get gif89 extension - this is currently ignored"

    |type blockSize subBlockSize

     aspNum aspDen left top width height cWidth cHeight fg bg

     animationType animationTime animationMask

     appID appAUTH

     iterationCount b ok|

    type := aStream nextByte.

    type == $R asciiValue ifTrue:[

        "/

        "/ Ratio extension

        "/

        'GIFREADER [info]: ratio extension ignored' infoPrintCR.

        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

        ].

        ^ self

    ].

    type == 16r01 ifTrue:[

        "/

        "/ plaintext extension

        "/

"/        'GIFREADER [info]: plaintext extension ignored' infoPrintCR.

        subBlockSize := aStream nextByte.

        left := aStream nextShortMSB:false.

        top := aStream nextShortMSB:false.

        width := aStream nextShortMSB:false.

        height := aStream nextShortMSB:false.

        cWidth := aStream nextByte.

        cHeight := aStream nextByte.

        fg := aStream nextByte.

        bg := aStream nextByte.

        aStream skip:12.

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

            aStream skip:subBlockSize

        ].

        ^ self

    ].

    type == 16rF9 ifTrue:[

        "/

        "/ graphic control extension

        "/

"/        'GIFREADER [info]: graphic control extension ignored' infoPrintCR.

        ].

        ^ self

    ].

    type == 16rFE ifTrue:[

        "/

        "/ comment extension

        "/

"/        'GIFREADER [info]: comment extension ignored' infoPrintCR.

        [(blockSize := aStream nextByte) ~~ 0] whileTrue:[

            aStream skip:blockSize

        ].

        ^ self

    ].

    type == 16rFF ifTrue:[

        "/

        "/  application extension

        "/

        subBlockSize := aStream nextByte.

        appID := (aStream nextBytes:8 ) asString.

        appAUTH := aStream nextBytes:3.

        subBlockSize := aStream nextByte.

        ok := false.

        appID = 'NETSCAPE' ifTrue:[

            appAUTH asString = '2.0' ifTrue:[

                subBlockSize == 3 ifTrue:[

                    b := aStream nextByte.

                    iterationCount := aStream nextShortMSB:false.

                    subBlockSize := aStream nextByte.

                    ok := true.

                ]

            ]

        ].

        ok ifFalse:[

            ('GIFREADER [info]: application extension (' , appID , ') ignored') infoPrintCR.

        ].