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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;
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();
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 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 = 2; i < row.size(); ++i)
for (size_t i = 1; i < row.size(); ++i)
row[i] += row[i - 1];
break;
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];
break;
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;
if (i > 1)
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 = 1; i < row.size(); ++i) {
for (size_t i = 0; i < row.size(); ++i) {
u8 left = 0;
u8 upper_left = 0;
if (i > 1) {
if (i > 0) {
left = 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;
decoded.append(row.slice(1));
decoded.append(row);
}
return decoded;