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libjpeg's `dct_method` is read by both the compressor and the decompressor, and `cjpeg`/`djpeg` both accept `-dct`, but the setting was reachable only through `Decompress::dct_method`. `Compress` keeps `cinfo` private, so a caller that wants to pick the encoder's DCT algorithm has no way to do it. Mirrors `Decompress::dct_method` exactly, reusing the existing `DctMethod` enum, and adds a test that encodes with each of the three methods.
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The fork's two commits were authored under the wrong Git identity: the scratch clone carried no repository-local `user.name`/`user.email` and fell back to this machine's global configuration, which is not the identity this project's OSS contributions belong under. Both fork branches were rewritten with the correct identity and force-pushed. The content is unchanged — `git diff` against the previous heads is empty — so this is an attribution fix, not a code change. - `[patch.crates-io]` rev is now 58f4e0ef91f2a0c477140734ef8b3fe5403befc3 - The upstream pull request's head is now 77c0dd48bcba2d8ba97c823edfea6eadaf8673ea Refs: ImageOptim/mozjpeg-rust#54
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Summary
Adds
Compress::set_dct_method, mirroring the existingDecompress::dct_method.libjpeg's
dct_methodfield is read by both the compressor and the decompressor, andcjpeg/djpegboth accept-dct islow|ifast|float. In this crate only the decompressionside is reachable:
Compresskeepscinfoprivate and exposes no setter, so a caller thatwants to choose the encoder's DCT algorithm has no way to do it and silently gets the
library default.
Motivation
I am porting a JPEG recompression tool from Go to Rust. Its CLI has always exposed
--dct float|ifast|islowas the encoder DCT/IDCT method — the Go binding it used appliedthe setting to both sides — so reproducing the flag needs this setter. Without it the flag
would have to be documented as decoder-only or dropped.
Changes
src/compress.rs:Compress::set_dct_method(&mut self, method: DctMethod), reusing theDctMethodenum already re-exported fromlib.rs, so no new public type is introduced.produces output with an SOI marker.
Notes
unsafeadded: the method writes a plain field oncinfo, exactly asDecompress::dct_methoddoes.Compressconvention (set_*) rather thanDecompress's baredct_method.cargo testpasses locally onaarch64-apple-darwin(18 lib tests, plus the integrationand doc test targets).