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LibPDF: Make filter byte not part of row in decode_png_prediction()

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No behavior change.
This commit is contained in:
Nico Weber 2023-11-16 19:48:50 -05:00 • committed by Andreas Kling
parent b763960fc2
commit 0416a07d56
1 changed files with 10 additions and 8 deletions
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18
Userland/Libraries/LibPDF/Filter.cpp
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@ -156,38 +156,40 @@ PDFErrorOr<ByteBuffer> Filter::decode_png_prediction(Bytes bytes, size_t bytes_p
ByteBuffer decoded; ByteBuffer decoded;
decoded.ensure_capacity(bytes.size() - number_of_rows); decoded.ensure_capacity(bytes.size() - number_of_rows);
auto empty_row = TRY(ByteBuffer::create_zeroed(bytes_per_row)); auto empty_row = TRY(ByteBuffer::create_zeroed(bytes_per_row - 1));
auto previous_row = empty_row.bytes(); auto previous_row = empty_row.bytes();
for (int row_index = 0; row_index < number_of_rows; ++row_index) { for (int row_index = 0; row_index < number_of_rows; ++row_index) {
auto row = Bytes { bytes.data() + row_index * bytes_per_row, bytes_per_row }; auto row = Bytes { bytes.data() + row_index * bytes_per_row, bytes_per_row };
auto filter = TRY(Gfx::PNG::filter_type(row[0])); auto filter = TRY(Gfx::PNG::filter_type(row[0]));
row = row.slice(1);
switch (filter) { switch (filter) {
case Gfx::PNG::FilterType::None: case Gfx::PNG::FilterType::None:
break; break;
case Gfx::PNG::FilterType::Sub: case Gfx::PNG::FilterType::Sub:
for (size_t i = 2; i < row.size(); ++i) for (size_t i = 1; i < row.size(); ++i)
row[i] += row[i - 1]; row[i] += row[i - 1];
break; break;
case Gfx::PNG::FilterType::Up: case Gfx::PNG::FilterType::Up:
for (size_t i = 1; i < row.size(); ++i) for (size_t i = 0; i < row.size(); ++i)
row[i] += previous_row[i]; row[i] += previous_row[i];
break; break;
case Gfx::PNG::FilterType::Average: case Gfx::PNG::FilterType::Average:
for (size_t i = 1; i < row.size(); ++i) { for (size_t i = 0; i < row.size(); ++i) {
u8 left = 0; u8 left = 0;
if (i > 1) if (i > 0)
left = row[i - 1]; left = row[i - 1];
u8 above = previous_row[i]; u8 above = previous_row[i];
row[i] += (left + above) / 2; row[i] += (left + above) / 2;
} }
break; break;
case Gfx::PNG::FilterType::Paeth: case Gfx::PNG::FilterType::Paeth:
for (size_t i = 1; i < row.size(); ++i) { for (size_t i = 0; i < row.size(); ++i) {
u8 left = 0; u8 left = 0;
u8 upper_left = 0; u8 upper_left = 0;
if (i > 1) { if (i > 0) {
left = row[i - 1]; left = row[i - 1];
upper_left = previous_row[i - 1]; upper_left = previous_row[i - 1];
} }
@ -198,7 +200,7 @@ PDFErrorOr<ByteBuffer> Filter::decode_png_prediction(Bytes bytes, size_t bytes_p
} }
previous_row = row; previous_row = row;
decoded.append(row.slice(1)); decoded.append(row);
} }
return decoded; return decoded;