Rewrite PNG parsing for minimal allocations#22297
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Overall approach looks good to me, some nitpicking
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Jan 15, 2026
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| // Drain remaining Zlib footer bytes if necessary. | ||
| Span<byte> drain = stackalloc byte[16]; | ||
| while (ds.Read(drain) > 0) { } |
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Why do we need to read these final bytes instead of just ignoring them?
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We have a contract for the stream to finish at the end of the chunk and consume the crc. I believe this wasn't called on any of D2K Png's, but lack of it was breaking some other png's
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When launching dune2k, now the only overheads in png constructor are from the C# decompressor. The dotnet decompressor quite a bit faster than zlib
PR:
Though from a broader PngSpriteSheet parser the performance seems to have increased by about 100%.
This rewrite removes as many allocations as possible, rather more relying on the stack and allocating much less of it. One of the most problematic parts was memory churn on collecting IDAT chunks with all their image data, then delaying processing them to the end chunk. Instead now we immediatelly parse all IDAT chunks without copying and stream them into the decompressor via custom stream.