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LibPDF: Let decode_png_prediction() call LibGfx's unfilter_scanline()

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It's less code, but it also fixes a bug: The implementation in
Filter.cpp used to use the previous byte as reference value, while
we're supposed to use the value of the previous channel as reference
(at least when a pixel is larger than one byte).
This commit is contained in:
Nico Weber 2023-11-16 20:08:33 -05:00 committed by Andreas Kling
parent 145ade3a86
commit 443b3eac77
Notes: sideshowbarker 2024-07-18 02:47:59 +09:00 
Author: https://github.com/nico
Commit: https://github.com/SerenityOS/serenity/commit/443b3eac77
Pull-request: https://github.com/SerenityOS/serenity/pull/21966
2 changed files with 6 additions and 37 deletions
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41
Userland/Libraries/LibPDF/Filter.cpp
View File

@ -9,7 +9,7 @@
#include <LibCompress/Deflate.h>
#include <LibCompress/LZWDecoder.h>
#include <LibGfx/ImageFormats/JPEGLoader.h>
#include <LibGfx/ImageFormats/PNGShared.h>
#include <LibGfx/ImageFormats/PNGLoader.h>
#include <LibPDF/CommonNames.h>
#include <LibPDF/Filter.h>
#include <LibPDF/Reader.h>
@ -149,7 +149,7 @@ PDFErrorOr<ByteBuffer> Filter::decode_ascii85(ReadonlyBytes bytes)
return buffer;
}
PDFErrorOr<ByteBuffer> Filter::decode_png_prediction(Bytes bytes, size_t bytes_per_row)
PDFErrorOr<ByteBuffer> Filter::decode_png_prediction(Bytes bytes, size_t bytes_per_row, size_t bytes_per_pixel)
{
int number_of_rows = bytes.size() / bytes_per_row;
@ -165,39 +165,7 @@ PDFErrorOr<ByteBuffer> Filter::decode_png_prediction(Bytes bytes, size_t bytes_p
auto filter = TRY(Gfx::PNG::filter_type(row[0]));
row = row.slice(1);
switch (filter) {
case Gfx::PNG::FilterType::None:
break;
case Gfx::PNG::FilterType::Sub:
for (size_t i = 1; i < row.size(); ++i)
row[i] += row[i - 1];
break;
case Gfx::PNG::FilterType::Up:
for (size_t i = 0; i < row.size(); ++i)
row[i] += previous_row[i];
break;
case Gfx::PNG::FilterType::Average:
for (size_t i = 0; i < row.size(); ++i) {
u8 left = 0;
if (i > 0)
left = row[i - 1];
u8 above = previous_row[i];
row[i] += (left + above) / 2;
}
break;
case Gfx::PNG::FilterType::Paeth:
for (size_t i = 0; i < row.size(); ++i) {
u8 left = 0;
u8 upper_left = 0;
if (i > 0) {
left = row[i - 1];
upper_left = previous_row[i - 1];
}
u8 above = previous_row[i];
row[i] += Gfx::PNG::paeth_predictor(left, above, upper_left);
}
break;
}
Gfx::PNGImageDecoderPlugin::unfilter_scanline(filter, row, previous_row, bytes_per_pixel);
previous_row = row;
decoded.append(row);
@ -224,7 +192,8 @@ PDFErrorOr<ByteBuffer> Filter::handle_lzw_and_flate_parameters(ByteBuffer buffer
if (buffer.size() % bytes_per_row)
return AK::Error::from_string_literal("Flate input data is not divisible into columns");
return decode_png_prediction(buffer, bytes_per_row);
size_t bytes_per_pixel = ceil_div(colors * bits_per_component, 8);
return decode_png_prediction(buffer, bytes_per_row, bytes_per_pixel);
}
PDFErrorOr<ByteBuffer> Filter::decode_lzw(ReadonlyBytes bytes, int predictor, int columns, int colors, int bits_per_component, int early_change)

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

@ -20,7 +20,7 @@ public:
private:
static PDFErrorOr<ByteBuffer> decode_ascii_hex(ReadonlyBytes bytes);
static PDFErrorOr<ByteBuffer> decode_ascii85(ReadonlyBytes bytes);
static PDFErrorOr<ByteBuffer> decode_png_prediction(Bytes bytes, size_t bytes_per_row);
static PDFErrorOr<ByteBuffer> decode_png_prediction(Bytes bytes, size_t bytes_per_row, size_t bytes_per_pixel);
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);