75 lines
2.5 KiB
OCaml
75 lines
2.5 KiB
OCaml
(* Read a non-interlaced, non-transparent 24 bit PNG for inclusion in a PDF file *)
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open Pdfutil
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open Pdfio
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type t =
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{width : int;
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height : int;
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idat : bytes}
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let string_of_tag t =
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Printf.sprintf "%c%c%c%c"
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(char_of_int (i32toi (Int32.shift_right t 24)))
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(char_of_int (i32toi (Int32.logand 0x000000FFl (Int32.shift_right t 16))))
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(char_of_int (i32toi (Int32.logand 0x000000FFl (Int32.shift_right t 8))))
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(char_of_int (i32toi (Int32.logand 0x000000FFl t)))
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let read_unsigned_4byte 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 (lsl32 a 24) (lsl32 b 16)) (lor32 (lsl32 c 8) d)
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let read_data l i =
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let l = i32toi l in
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let b = mkbytes l in
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setinit i b 0 l;
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b
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let read_chunk i =
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let chunklen = read_unsigned_4byte i in
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let chunktype = read_unsigned_4byte i in
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let chunkdata = read_data chunklen i in
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let _ (* crc *) = read_unsigned_4byte i in
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(string_of_tag chunktype, chunkdata)
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let concat_bytes ss =
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let total_length = sum (map bytes_size ss) in
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let s' = mkbytes total_length in
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let p = ref 0 in
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iter
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(fun s ->
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for x = 0 to bytes_size s - 1 do bset_unsafe s' !p (bget s x); incr p done)
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ss;
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s'
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let read_png i =
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try
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i.seek_in 8;
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let ihdr, ihdrdata = read_chunk i in
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if ihdr <> "IHDR" then raise (Pdf.PDFError "read_png: first table not IHDR") else
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let hdr = input_of_bytes ihdrdata in
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let width = read_unsigned_4byte hdr in
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let height = read_unsigned_4byte hdr in
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let bitdepth = hdr.input_byte () in
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if bitdepth <> 8 then failwith "read_png: bit depth not 8" else
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let colortype = hdr.input_byte () in
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if colortype <> 2 then failwith "read_png: only 24 bit non-alpha PNGs" else
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let _ (*compressionmethod*) = hdr.input_byte () in
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let _ (*filtermethod*) = hdr.input_byte () in
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let interlacemethod = hdr.input_byte () in
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if interlacemethod <> 0 then failwith "read_png: interlaced PDFs not supported" else
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let idat = ref [] in
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begin try
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while true do
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let chunkname, chunkdata = read_chunk i in
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if chunkname = "IDAT" then idat := chunkdata::!idat
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done
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with
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_ -> ()
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end;
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{width = i32toi width; height = i32toi height; idat = concat_bytes (rev !idat)}
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with
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e -> raise (Pdf.PDFError (Printf.sprintf "read_png: failed on %s" (Printexc.to_string e)))
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