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LibGfx/JPEG: More support for scans with a single component

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Introduced in 2c98eff, support for non-interleaved scans was not working
for frames with a number of MCU per line or column that is odd. Indeed,
the decoder assumed that they have scans that include a fabricated MCU
like scans with multiple components.

This patch makes the decoder handle images with a number of MCU per line
or column that is odd. To do so, as in the current decoder state we do
not know if components are interleaved at allocation time, we skip over
falsely-created macroblocks when filling them. As stated in 2c98eff,
this is probably not a good solution and a whole refactor will be
welcome.

It also comes with a test that open a square image with a side of 600px,
meaning 75 MCUs.
This commit is contained in:
Lucas CHOLLET 2023-03-03 23:45:47 -05:00 committed by Jelle Raaijmakers
parent b820f9ffbd
commit 3f9c5af553
Notes: sideshowbarker 2024-07-17 06:00:02 +09:00 
Author: https://github.com/LucasChollet
Commit: https://github.com/SerenityOS/serenity/commit/3f9c5af553
Pull-request: https://github.com/SerenityOS/serenity/pull/17709
Reviewed-by: https://github.com/gmta ✅
Reviewed-by: https://github.com/kennethmyhra
Reviewed-by: https://github.com/nico
3 changed files with 24 additions and 1 deletions
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11
Tests/LibGfx/TestImageDecoder.cpp
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@ -134,6 +134,17 @@ TEST_CASE(test_jpeg_sof2_spectral_selection)
EXPECT_EQ(frame.image->size(), Gfx::IntSize(592, 800));
}
TEST_CASE(test_jpeg_sof0_several_scans_odd_number_mcu)
{
auto file = MUST(Core::MappedFile::map(TEST_INPUT("several_scans_odd_number_mcu.jpg"sv)));
EXPECT(Gfx::JPEGImageDecoderPlugin::sniff(file->bytes()));
auto plugin_decoder = MUST(Gfx::JPEGImageDecoderPlugin::create(file->bytes()));
EXPECT(plugin_decoder->initialize());
auto frame = MUST(plugin_decoder->frame(0));
EXPECT_EQ(frame.image->size(), Gfx::IntSize(600, 600));
}
TEST_CASE(test_pbm)
{
auto file = MUST(Core::MappedFile::map(TEST_INPUT("buggie-raw.pbm"sv)));

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Tests/LibGfx/test-inputs/several_scans_odd_number_mcu.jpg Normal file
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14
Userland/Libraries/LibGfx/ImageFormats/JPEGLoader.cpp
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@ -446,9 +446,21 @@ static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macro
for (u8 hfactor_i = 0; hfactor_i < scan_component.component.hsample_factor; hfactor_i++) {
// A.2.3 - Interleaved order
u32 macroblock_index = (vcursor + vfactor_i) * context.mblock_meta.hpadded_count + (hfactor_i + hcursor);
if (!context.current_scan.are_components_interleaved())
if (!context.current_scan.are_components_interleaved()) {
macroblock_index = vcursor * context.mblock_meta.hpadded_count + (hfactor_i + (hcursor * scan_component.component.vsample_factor) + (vfactor_i * scan_component.component.hsample_factor));
// A.2.4 Completion of partial MCU
// If the component is [and only if!] to be interleaved, the encoding process
// shall also extend the number of samples by one or more additional blocks.
// Horizontally
if (macroblock_index >= context.mblock_meta.hcount && macroblock_index % context.mblock_meta.hpadded_count >= context.mblock_meta.hcount)
continue;
// Vertically
if (macroblock_index >= context.mblock_meta.hpadded_count * context.mblock_meta.vcount)
continue;
}
// 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;