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LibGfx: Don't assume that a scan include all components for the image

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A scan can contain fewer components that the full image. However, if
there is multiple components, they have to follow the ordering of the
frame header. It means that we can loop over components of the image
and skip those that doesn't correspond.
This commit is contained in:
Lucas CHOLLET 2023-02-25 15:31:22 -05:00 • committed by Andreas Kling
parent 947698f29f
commit ae124c19ef
1 changed files with 18 additions and 9 deletions
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27
Userland/Libraries/LibGfx/JPEGLoader.cpp
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@ -135,7 +135,7 @@ struct Component {
u8 vsample_factor { 1 }; // Vi, Vertical sampling factor
u8 qtable_id { 0 }; // Tqi, Quantization table destination selector
// The JPEG specification does not specify which component correspond to
// The JPEG specification does not specify which component corresponds to
// Y, Cb or Cr. This field (actually the index in the parent Vector) will
// act as an authority to determine the *real* component.
// Please note that this is implementation specific.
@ -547,6 +547,8 @@ static inline ErrorOr<Marker> read_marker_at_cursor(Stream& stream)
static ErrorOr<void> read_start_of_scan(AK::SeekableStream& stream, JPEGLoadingContext& context)
{
// B.2.3 - Scan header syntax
if (context.state < JPEGLoadingContext::State::FrameDecoded) {
dbgln_if(JPEG_DEBUG, "{}: SOS found before reading a SOF!", TRY(stream.tell()));
return Error::from_string_literal("SOS found before reading a SOF");
@ -554,23 +556,30 @@ static ErrorOr<void> read_start_of_scan(AK::SeekableStream& stream, JPEGLoadingC
u16 bytes_to_read = TRY(stream.read_value<BigEndian<u16>>()) - 2;
TRY(ensure_bounds_okay(TRY(stream.tell()), bytes_to_read, context.data_size));
[[maybe_unused]] u8 const component_count = TRY(stream.read_value<u8>());
u8 const component_count = TRY(stream.read_value<u8>());
Scan current_scan;
Optional<u8> last_read;
u8 component_read = 0;
for (auto& component : context.components) {
u8 component_id = TRY(stream.read_value<u8>());
// See the Csj paragraph:
// [...] the ordering in the scan header shall follow the ordering in the frame header.
if (component_read == component_count)
break;
if (component.id != component_id) {
dbgln("JPEG decode failed (component.id != component_id)");
return Error::from_string_literal("JPEG decode failed (component.id != component_id)");
}
if (!last_read.has_value())
last_read = TRY(stream.read_value<u8>());
if (component.id != *last_read)
continue;
u8 table_ids = TRY(stream.read_value<u8>());
ScanComponent scan_component { component, static_cast<u8>(table_ids >> 4), static_cast<u8>(table_ids & 0x0F) };
current_scan.components.empend(component, static_cast<u8>(table_ids >> 4), static_cast<u8>(table_ids & 0x0F));
current_scan.components.append(scan_component);
component_read++;
last_read.clear();
}
current_scan.spectral_selection_start = TRY(stream.read_value<u8>());