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LibGfx/JPEG: Support End-Of-Bands run

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This patch brings support for SOF2 JPEGs that only use spectral
selection :^)

We still don't have achieved full support for SOF2 images, but as an
example, we decode progressive JPEG from Cloudinary.
This commit is contained in:
Lucas CHOLLET 2023-02-26 00:09:56 -05:00 • committed by Linus Groh
parent e5385cdf24
commit 1926a86336
Notes: sideshowbarker 2024-07-17 11:29:41 +09:00
1 changed files with 31 additions and 1 deletions

32
Userland/Libraries/LibGfx/JPEGLoader.cpp
View file

@ -205,6 +205,8 @@ struct Scan {
HuffmanStreamState huffman_stream;
u64 end_of_bands_run_count { 0 };
// See the note on Figure B.4 - Scan header syntax
bool are_components_interleaved() const
{
@ -335,6 +337,24 @@ static ErrorOr<void> add_dc(JPEGLoadingContext& context, Macroblock& macroblock,
return {};
}
static ErrorOr<bool> read_eob(Scan& scan, u32 symbol)
{
// G.1.2.2 - Progressive encoding of AC coefficients with Huffman coding
// Note: We also use it for non-progressive encoding as it supports both EOB and ZRL
if (auto const eob = symbol & 0x0F; eob == 0 && symbol != JPEG_ZRL) {
// We encountered an EOB marker
auto const eob_base = symbol >> 4;
auto const additional_value = TRY(read_huffman_bits(scan.huffman_stream, eob_base));
scan.end_of_bands_run_count = additional_value + (1 << eob_base) - 1;
return true;
}
return false;
}
static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock, ScanComponent const& scan_component)
{
auto& ac_table = context.ac_tables.find(scan_component.ac_destination_id)->value;
@ -352,7 +372,8 @@ static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock,
// number of zeroes to be stuffed before reading the coefficient. Low 4
// bits represent the magnitude of the coefficient.
auto ac_symbol = TRY(get_next_symbol(scan.huffman_stream, ac_table));
if (ac_symbol == 0)
if (TRY(read_eob(scan, ac_symbol)))
break;
// ac_symbol = JPEG_ZRL means we need to skip 16 zeroes.
@ -412,6 +433,12 @@ static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macro
if (!context.current_scan.are_components_interleaved())
mb_index = vcursor * context.mblock_meta.hpadded_count + (hfactor_i + (hcursor * scan_component.component.vsample_factor) + (vfactor_i * scan_component.component.hsample_factor));
// G.1.2.2 - Progressive encoding of AC coefficients with Huffman coding
if (context.current_scan.end_of_bands_run_count > 0) {
--context.current_scan.end_of_bands_run_count;
continue;
}
Macroblock& block = macroblocks[mb_index];
if (context.current_scan.spectral_selection_start == 0)
@ -438,6 +465,9 @@ static bool is_dct_based(StartOfFrame::FrameType frame_type)
static void reset_decoder(JPEGLoadingContext& context)
{
// G.1.2.2 - Progressive encoding of AC coefficients with Huffman coding
context.current_scan.end_of_bands_run_count = 0;
// E.2.4 Control procedure for decoding a restart interval
if (is_dct_based(context.frame.type)) {
context.previous_dc_values[0] = 0;