<<>>
<<AISFileFormat.mesa>>
<<Copyright Ó 1984, 1985, 1986, 1987, 1988, 1992 by Xerox Corporation.  All rights reserved.>>
<<Doug Wyatt, February 22, 1986 2: 53: 48 pm PST>>
<<Michael Plass, February 11, 1988 10:11:44 am PST>>

    DIRECTORY Basics USING [HWORD];

    AISFileFormat: CEDAR DEFINITIONS
    ~ BEGIN

        Card16: TYPE ~ Basics.HWORD; -- big-endian 16-bit unsigned number
        Int16: TYPE ~ Basics.HWORD; -- big-endian 16-bit signed number

        bitsPerAISWord: NAT ~ 16; -- an AIS "word" is 16 bits
        wordsPerAISPage: NAT ~ 1024; -- an AIS "page" is 1024 "words"
        bytesPerAISWord: NAT ~ bitsPerAISWord/8;
        bytesPerAISPage: NAT ~ bytesPerAISWord*wordsPerAISPage;

        zero: Basics.HWORD ~ [0, 0];
        nil: Basics.HWORD ~ [BYTE.LAST, BYTE.LAST]; -- commonly used for a nil value

        passwordValue: Basics.HWORD ~ [hi: 84H, lo: 0AAH];  -- = -31574

        AttributeHeader: TYPE ~ MACHINE DEPENDENT RECORD[
            password(0:0..15): Card16, -- password, must equal passwordValue
            length(0:16..31): Card16 -- length in 16-bit words of attribute section, including this header
        <<length must be a multiple of wordsPerAISPage>>
            ];
        byteSizeAttributeHeader: NAT ~ BYTES[AttributeHeader];

        PartHeader: TYPE ~ MACHINE DEPENDENT RECORD[
            type(0:0..5): PartType, -- type of attribute part
            lengthHi(0:6..7): [0..4), lengthLo(0:8..15): BYTE
            <<(256*lengthHi+lengthLo) = length of part in 16-bit words, including this one>>
            ];
        byteSizePartHeader: NAT ~ BYTES[PartHeader];
    <<>>
        PartType: TYPE ~ MACHINE DEPENDENT {
            nil(0), -- no more parts
            raster(1), -- RasterPart follows
            placement(2), -- PlacementPart follows
            photometry(3), -- PhotometryPart follows
            comment(4), -- CommentPart follows
            (77B)
            };

        RasterPart: TYPE ~ MACHINE DEPENDENT RECORD[
            scanCount(0:0..15): Card16,  -- number of scan lines
            scanLength(0:16..31): Card16,  -- pixels per scan line
            scanDirection(0:32..47): ScanDirection,  -- scanning directions
            samplesPerPixel(0:48..63): Card16,  -- number of samples
            codingTypeHi(0:64..71): BYTE, -- currently always 0
            codingType(0:72..79): CodingType, -- method of coding
            pad(0:80..95): Card16 -- pad to multiple of 32 bits (not in file)
            ];
        byteSizeRasterPart: NAT ~ BYTES[RasterPart]-BYTES[Card16];
    <<>>
        ScanDirection: TYPE ~ Card16;
        <<There may not be universal agreement on the interpretation of this value.  The AIS documentation disagrees with (at least some 
        versions of) AISFile.d.  Fortunately, the two most commonly used values are unambiguous: >>
        <<3 => pixels go toward the right of the page, scan lines toward the bottom>>
        <<0, 8 => pixels go toward the top of the page, scan lines toward the right>>

        CodingType: TYPE ~ MACHINE DEPENDENT {
            nil(0), -- undefined
            uca(1), -- UCACoding folllows
            (255)
            };

        UCACoding: TYPE ~ MACHINE DEPENDENT RECORD[ -- UnCompressedArray
            bitsPerSample(0:0..15): Card16,  -- number of bits for each sample
            wordsPerScanLine(0:16..31): Card16,  -- number of 16-bit words per scan line
            scanLinesPerBlock(0:32..47): Card16,  -- scan lines in each block,  nil if no blocks
            paddingPerBlock(0:48..63): Card16 -- words of padding at end of block,  nil if no blocks
            ];
        byteSizeUCACoding: NAT ~ BYTES[UCACoding];

        PlacementPart: TYPE ~ MACHINE DEPENDENT RECORD[
            xLeft(0:0..15): Int16,  -- position of lower left corner
            yBottom(0:16..31): Int16, 
            xWidth(0:32..47): Int16,  -- size of image area on page
            yHeight(0:48..63): Int16
            ];
        byteSizePlacementPart: NAT ~ BYTES[PlacementPart];

        PhotometryPart: TYPE ~ MACHINE DEPENDENT RECORD[
            signalHi(0:0..7): BYTE ¬ 0,  -- currently always 0 or 255
            signal(0:8..15): SignalType ¬ bw,  -- what type of signal is sampled
            sense(0:16..31): Card16 ¬ zero,  -- larger sample values are lighter if sense=0,  else darker
            scaleHi(0:32..39): BYTE ¬ 0,  -- currently always 0 or 255
            scale(0:40..47): ScaleType ¬ nil,  -- specifies the conversion between physical and sample values
            scaleA(0:48..79),  scaleB(0:80..111),  scaleC(0:112..143): Value ¬ [zero,  zero], 
            spotTypeHi(0:144..151): BYTE ¬ 0,  -- currently always 0 or 255
            spotType(0:152..159): SpotType ¬ nil,  -- spot type
            spotWidth(0:160..175): Card16 ¬ nil,  -- in units of 100*(width in pixels)
            spotLength(0:176..191): Card16 ¬ nil,  -- in units of 100*(length in scanlines)
            sampleMin(0:192..207): Int16 ¬ nil,  -- sample range,  if known
            sampleMax(0:208..223): Int16 ¬ nil, 
            histogramLength(0:224..239): Card16 ¬ zero, -- number of words in histogram,  nil if no histogram
            pad(0:240..255): Card16 ¬ zero -- pad to multiple of 32 bits (not in file)
            ];
        byteSizePhotometryPart: NAT ~ BYTES[PhotometryPart]-BYTES[Card16];

        SignalType: TYPE ~ MACHINE DEPENDENT {
            bw(0), -- black and white
            red(1), -- red separation
            blue(2), -- blue separation
            green(3), -- green separation
            cyan(4), -- cyan separation
            magenta(5), -- magenta separation
            yellow(6), -- yellow separation
            x(7), -- x signal (CIE)
            y(8), -- y signal
            RGB(100), -- red, green, blue samples, 3 per pixel
            CMY(101), -- cyan, magenta, yellow samples, 3 per pixel
            CMYB(102), -- cyan, magenta, yellow, black samples, 4 per pixel
            Yxy(103), -- Y, x, y (CIE) samples, 3 per pixel
            comments(376B), -- specified in comments
            undefined(377B) -- undefined
            };

        ScaleType: TYPE ~ MACHINE DEPENDENT {
            nil(0), -- undefined
            reflectance(1), -- reflectance or transmittance
            density(2), -- optical density
            comments(376B), -- specified in comments
            undefined(377B) -- undefined
            };

        Value: TYPE ~ MACHINE DEPENDENT RECORD[
            sample(0:0..15): Int16,  -- 1000*(actual reflectance or density)
            level(0:16..31): Card16 -- corresponding digital sample value
            ];

        SpotType: TYPE ~ MACHINE DEPENDENT {
            nil(0), -- undefined
            rectangular(1), -- spotWidth by spotLength
            circular(2), -- diameter=spotWidth, spotLength is undefined
            comments(376B), -- specified in comments
            undefined(377B) -- undefined
            };

        histogramScale: Int16 ~ [hi: 32767 / 256, lo: 32767 MOD 256];

        CommentPart: TYPE ~ BCPLStringBody;
        byteSizeCommentPart: NAT ~ BYTES[CommentPart]; -- maximum

        BCPLStringBody: TYPE ~ PACKED ARRAY [0..256) OF CHAR;
        <<If s is a POINTER TO BCPLStringBody, length is ORD[s[0]], text is s[1..length]>>

    END.