41 lines
1.2 KiB
OCaml
41 lines
1.2 KiB
OCaml
open Pdfutil
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open Pdfio
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open Cpdferror
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let read_word i =
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let a = i32ofi (i.input_byte ()) in
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let b = i32ofi (i.input_byte ()) in
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let c = i32ofi (i.input_byte ()) in
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let d = i32ofi (i.input_byte ()) in
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lor32 (lor32 (lor32 (lsl32 a 24) (lsl32 b 16)) (lsl32 c 8)) d
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exception Answer of int * int
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let id_IMAGE_HEADER_BOX = 0x69686472l (* ihdr *)
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(* Return the width and height of a JPEG2000 (.jp2 or .jpx) image. *)
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let jpeg2000_dimensions_inner bs =
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let i = Pdfio.input_of_bytes bs in
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let a = read_word i in
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let b = read_word i in
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let c = read_word i in
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if a <> 0x0000000cl || b <> 0x6a502020l || c <> 0x0d0a870al then
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Cpdferror.error "bad JPEG2000 header"
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else
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while true do
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let box = read_word i in
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if box = id_IMAGE_HEADER_BOX then
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begin
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let h = read_word i in
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let w = read_word i in
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raise (Answer (i32toi w, i32toi h))
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end;
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(* Read words starting at each byte until we find ihdr. *)
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i.seek_in (i.pos_in () - 3)
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done
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let jpeg2000_dimensions bs =
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try jpeg2000_dimensions_inner bs; (0, 0) with
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| Answer (w, h) -> (w, h)
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| Exit -> error "could not determine JPEG2000 dimensions"
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