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LibPDF: Add support for the LZW filter

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This allows us to decode the first page of ThinkingInPostScript.pdf :^)
This commit is contained in:
Lucas CHOLLET 2023-11-11 17:00:02 -05:00 • committed by Andreas Kling
parent 048ef11136
commit 9bc25db9a3
3 changed files with 33 additions and 4 deletions
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1
Userland/Libraries/LibPDF/CommonNames.h
View file

@ -61,6 +61,7 @@
X(Differences) \
X(Domain) \
X(E) \
X(EarlyChange) \
X(Encode) \
X(Encoding) \
X(Encrypt) \

34
Userland/Libraries/LibPDF/Filter.cpp
View file

@ -4,8 +4,10 @@
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/BitStream.h>
#include <AK/Hex.h>
#include <LibCompress/Deflate.h>
#include <LibCompress/LZWDecoder.h>
#include <LibGfx/ImageFormats/JPEGLoader.h>
#include <LibPDF/CommonNames.h>
#include <LibPDF/Filter.h>
@ -18,6 +20,7 @@ PDFErrorOr<ByteBuffer> Filter::decode(ReadonlyBytes bytes, DeprecatedFlyString c
int columns = 1;
int colors = 1;
int bits_per_component = 8;
int early_change = 1;
if (decode_parms) {
if (decode_parms->contains(CommonNames::Predictor))
@ -28,6 +31,8 @@ PDFErrorOr<ByteBuffer> Filter::decode(ReadonlyBytes bytes, DeprecatedFlyString c
colors = decode_parms->get_value(CommonNames::Colors).get<int>();
if (decode_parms->contains(CommonNames::BitsPerComponent))
bits_per_component = decode_parms->get_value(CommonNames::BitsPerComponent).get<int>();
if (decode_parms->contains(CommonNames::EarlyChange))
early_change = decode_parms->get_value(CommonNames::EarlyChange).get<int>();
}
if (encoding_type == CommonNames::ASCIIHexDecode)
@ -35,7 +40,7 @@ PDFErrorOr<ByteBuffer> Filter::decode(ReadonlyBytes bytes, DeprecatedFlyString c
if (encoding_type == CommonNames::ASCII85Decode)
return decode_ascii85(bytes);
if (encoding_type == CommonNames::LZWDecode)
return decode_lzw(bytes);
return decode_lzw(bytes, predictor, columns, colors, bits_per_component, early_change);
if (encoding_type == CommonNames::FlateDecode)
return decode_flate(bytes, predictor, columns, colors, bits_per_component);
if (encoding_type == CommonNames::RunLengthDecode)
@ -227,9 +232,32 @@ PDFErrorOr<ByteBuffer> Filter::handle_lzw_and_flate_parameters(ByteBuffer buffer
return decode_png_prediction(buffer, bytes_per_row);
}
PDFErrorOr<ByteBuffer> Filter::decode_lzw(ReadonlyBytes)
PDFErrorOr<ByteBuffer> Filter::decode_lzw(ReadonlyBytes bytes, int predictor, int columns, int colors, int bits_per_component, int early_change)
{
return Error::rendering_unsupported_error("LZW Filter is not supported");
auto memory_stream = make<FixedMemoryStream>(bytes);
auto lzw_stream = make<BigEndianInputBitStream>(MaybeOwned<Stream>(move(memory_stream)));
Compress::LZWDecoder lzw_decoder { MaybeOwned<BigEndianInputBitStream> { move(lzw_stream) }, 8, -early_change };
ByteBuffer decoded;
u16 const clear_code = lzw_decoder.add_control_code();
u16 const end_of_data_code = lzw_decoder.add_control_code();
while (true) {
auto const code = TRY(lzw_decoder.next_code());
if (code == clear_code) {
lzw_decoder.reset();
continue;
}
if (code == end_of_data_code)
break;
TRY(decoded.try_append(lzw_decoder.get_output()));
}
return handle_lzw_and_flate_parameters(move(decoded), predictor, columns, colors, bits_per_component);
}
PDFErrorOr<ByteBuffer> Filter::decode_flate(ReadonlyBytes bytes, int predictor, int columns, int colors, int bits_per_component)

2
Userland/Libraries/LibPDF/Filter.h
View file

@ -21,7 +21,7 @@ private:
static PDFErrorOr<ByteBuffer> decode_ascii_hex(ReadonlyBytes bytes);
static PDFErrorOr<ByteBuffer> decode_ascii85(ReadonlyBytes bytes);
static PDFErrorOr<ByteBuffer> decode_png_prediction(Bytes bytes, int bytes_per_row);
static PDFErrorOr<ByteBuffer> decode_lzw(ReadonlyBytes bytes);
static PDFErrorOr<ByteBuffer> decode_lzw(ReadonlyBytes bytes, int predictor, int columns, int colors, int bits_per_component, int early_change);
static PDFErrorOr<ByteBuffer> decode_flate(ReadonlyBytes bytes, int predictor, int columns, int colors, int bits_per_component);
static PDFErrorOr<ByteBuffer> decode_run_length(ReadonlyBytes bytes);
static PDFErrorOr<ByteBuffer> decode_ccitt(ReadonlyBytes bytes);