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47 lines
1.0 KiB
Racket
47 lines
1.0 KiB
Racket
8 years ago
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#lang br
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gif-file : header logical-screen-descriptor global-color-table middle trailer
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header : signature version
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signature : #"GIF"
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version : u1{3} => bytes->string
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logical-screen-descriptor : width height packed bgcolor-idx aspect
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width : u2
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height : u2
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packed : color-table-flag color-res sort-flag color-table-size
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bgcolor-idx : u1
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aspect : u1
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color-table-flag : b{1} => ->integer
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color-res : b{3}
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sort-flag : b{1}
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color-table-size : b{3}
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color-table-colors (size->colors color-table-size)
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global-color-table : color-rec{color-table-flag * color-table-colors}
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color-rec : red green blue
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red : u1
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blue : u1
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green : u1
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middle: gfx-control-ext img-descriptor lct? image-data
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gfx-control-ext : u1{8}
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img-descriptor : img-separator left top width height img-packed
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img-separator : #"2C"
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left : u2
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top : u2
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width : u2
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height : u2
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img-packed : lct-flag interlace sort res lct-size
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lct-flag : b
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interlace : b
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sort : b
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res : b{2}
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lct-size : b{3}
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lct: color-rec{lct-flag * (size->colors lct-size)}
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image-data : lzw-size data-subblock
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