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69964e10f4
JPEGs can store a `restart_interval`, which controls how many minimum coded units (MCUs) apart the stream state resets. This can be used for error correction, decoding parts of a jpeg in parallel, etc. We tried to use u32 i = vcursor * context.mblock_meta.hpadded_count + hcursor; i % (context.dc_restart_interval * context.sampling_factors.vertical * context.sampling_factors.horizontal) == 0 to check if we hit a multiple of an MCU. `hcursor` is the horizontal offset into 8x8 blocks, vcursor the vertical offset, and hpadded_count stores how many 8x8 blocks we have per row, padded to a multiple of the sampling factor. This isn't quite right if hcursor isn't divisible by both the vertical and horizontal sampling factor. Tweak things so that they work. Also rename `i` to `number_of_mcus_decoded_so_far` since that what it is, at least now. For the test case, I converted an existing image to a ppm: Build/lagom/bin/image -o out.ppm \ Tests/LibGfx/test-inputs/jpg/12-bit.jpg Then I resized it to 102x77px in Photoshop and saved it again. Then I turned it into a jpeg like so: path/to/cjpeg \ -outfile Tests/LibGfx/test-inputs/jpg/odd-restart.jpg \ -sample 2x2,1x1,1x1 -quality 5 -restart 3B out.ppm The trick here is to: a) Pick a size that's not divisible by the data size width (8), and that when rounded to a block size (13) still isn't divisible by the subsample factor -- done by picking a width of 102. b) Pick a huffman table that doesn't happen to contain the bit pattern for a restart marker, so that reading a restart marker from the bitstream as data causes a failure (-quality 5 happens to do this) c) Pick a restart interval where we fail to skip it if our calculation is off (-restart 3B) Together with #22987, fixes #22780. |
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.. | ||
AK | ||
JSSpecCompiler | ||
Kernel | ||
LibAudio | ||
LibC | ||
LibCompress | ||
LibCore | ||
LibCpp | ||
LibCrypto | ||
LibDiff | ||
LibEDID | ||
LibELF | ||
LibGfx | ||
LibGL | ||
LibGLSL | ||
LibIMAP | ||
LibJS | ||
LibLocale | ||
LibMarkdown | ||
LibPDF | ||
LibRegex | ||
LibSQL | ||
LibTest | ||
LibTextCodec | ||
LibThreading | ||
LibTimeZone | ||
LibTLS | ||
LibTTF | ||
LibUnicode | ||
LibVideo | ||
LibWasm | ||
LibWeb | ||
LibWebView | ||
LibXML | ||
Spreadsheet | ||
UserspaceEmulator | ||
Utilities | ||
CMakeLists.txt |