chore(deps): update module github.com/go-gfx/gfx to v0.16.0 - autoclosed

[tannevaled]

This PR contains the following updates:

Package	Type	Update	Change
github.com/go-gfx/gfx	require	minor	v0.1.0 → v0.16.0

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Release Notes

go-gfx/gfx (github.com/go-gfx/gfx)

v0.16.0: — the registry writes too

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codec.Encode writes PNG, JPEG, GIF, TIFF and BMP, each through the same reference library that reads it. Nothing here encodes anything itself.

The registry could read eleven formats and write none, so every consumer that had a picture and needed a file wrote its own encoder call — and a PDF toolkit that can draw a page could not offer "PDF to PNG".

Reading and writing are not symmetric, and the gap is not an oversight: a reference decoder exists in pure Go for every format Sniff names, a reference encoder for five of them. WEBP, ICO, ICNS, PNM, QOI, JP2 and JBIG2 return ErrCannotEncode rather than something in another format under the asked-for name. CanEncode says which way a format goes without having to fail to find out.

Alpha survives into PNG and TIFF. The other three do not, and what they are given is the image composited onto white — chosen here rather than left to the encoder, because an encoder that simply drops the channel puts the colour that was under the transparency into the file, and for a page drawn on transparent ground that is black.

100% statement coverage, go vet and -race clean, nine cross-compile targets, CGO-free.

v0.15.0: — a JBIG2 decoder that reads real scans

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The JBIG2 decoder now comes from a fork carrying one fix, offered upstream as dkrisman/gobig2#2.

Upstream's per-symbol pixel cap defaults to 4 megapixels, on the reasoning that a real glyph is "tens of pixels per side". Real scanned documents disagree: some encoders emit a page-sized region as one symbol. Of 403 JBIG2 streams taken from the /Mask and /SMask entries of public Internet Archive scans, 7 are refused at that default — they need between 7 and 8 MP for a single symbol, and poppler reads all of them at its own defaults.

A consumer could not simply raise it: the limits are process-global variables, so a library that raised them would raise them for everything else in the binary.

The fix defaults the per-symbol cap to the aggregate cap, which is charged for every symbol three statements later and so already bounds the work — a per-symbol cap below the aggregate forbids a shape, not an amount of work.

With it the same 403 streams decode 403 of 403, every one bit-exact with poppler's own decoder, compared by extracting the image rather than rendering the page.

The fork also ends this module's dependency on an untagged one. It is meant to end: the day upstream tags a release carrying the fix, this goes back.

100% statement coverage, go vet and -race clean, nine cross-compile targets, CGO-free.

v0.14.0: — the JBIG2 a container embeds

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codec.DecodeEmbeddedJBIG2 reads the headerless form of JBIG2 — segments and nothing else, with the shared ones handed in separately — which is what a PDF stores in a /JBIG2Decode stream.

v0.13.0 added JBIG2 as a file. The embedded form carries no signature and its globals cannot be guessed from the stream, so it cannot be sniffed and sits outside Decode's contract on purpose.

It is here so that one package names the JBIG2 decoder. That matters more than usual for this format: the reference decoder's resource limits are process-global rather than per-decode, so a library cannot raise them without changing them for everything else in the binary, and it publishes no tagged version.

Globals that make no sense do not stop a stream that does not read them — which is nearly all of them. Of 403 JBIG2 streams in a corpus of scanned documents, none named a globals stream.

100% statement coverage, go vet and -race clean, nine cross-compile targets, CGO-free.

v0.13.0: — JBIG2, the ink layer of a scanned page

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codec reads JBIG2, the format a scanned page's ink is stored in. A modern scan is two images — a low-resolution colour background as JPEG 2000, and a high-resolution bitonal ink layer over it as JBIG2. v0.12.0 could read the background; this reads the ink.

No decoder is reimplemented, as for every other format in the package. Choosing the reference was the work: four pure-Go candidates exist and all four advertise full segment coverage. 403 JBIG2 masks were extracted from real scanned documents and every pixel compared against poppler's own decoder.

decoder	decoded	identical to poppler
dkrisman/gobig2	396/403	396 — 100%
jdeng/gojbig2	399/403	37 — 9%
dobbo-ca/byblos	157/403	157 — 100% (generic region only)
xiaoqidun/jbig2	0/403	—

The candidate that decodes the most is wrong nearly everywhere. Counting successes would have picked it; comparing pixels is what did not.

The headerless form a PDF embeds carries no signature and is deliberately not sniffed — a PDF consumer learns the format from the image dictionary. TestTheEmbeddedFormCarriesNoSignature holds that line.

100% statement coverage, go vet and -race clean, nine cross-compile targets including big-endian s390x, CGO_ENABLED=0.

v0.12.0: — JPEG 2000, which is what a scanned page is stored in

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JPEG 2000 — which is what a scanned page is stored in

This package reimplements no decoder. It sniffs a container and hands it to a pure-Go reference. JPEG 2000 was the one shape it did not know, and that mattered more than anyone had measured.

Extending the corpus to where a scanned page actually lives says so plainly. Per population, the share of documents carrying a JPEG 2000 image, and the pages that have nothing else on them at all:

population	documents	pages blank without it
biodiversity scans	250 of 250 (100.0%)	310
medical heritage	248 of 250 (99.2%)	278
scanned books	144 of 222 (64.9%)	67
court filings	2 of 250 (0.8%)	0
government forms	4 of 450 (0.9%)	0

The last two rows are why this was nearly not done. Measured over forms alone, JPEG 2000 looks like eleven files in sixteen hundred and not worth a decoder. That figure was about the corpus, not about the world.

Not written here, and not written at all

github.com/ajroetker/go-jpeg2000 is 20 050 lines of pure Go — EBCOT, the wavelet transforms, the MQ coder, tag trees, packets, both the JP2 container and the bare codestream, decoder and encoder, with its own conformance suite and no cgo. Writing a second one would be the reference-library rule broken in its plainest case.

Checked rather than assumed:

• it builds for all nine targets this fleet ships, js/wasm and s390x included, despite carrying a SIMD dependency;
• it decodes 1 610 of 1 610 real JPEG 2000 images taken out of eighty scanned books, with no refusals.

Two shapes, one picture

A JP2 file opens with the twelve-byte signature box. A PDF's /JPXDecode stream is usually the bare codestream, which opens with SOC immediately followed by SIZ. Sniff knows both, because in the wild almost every scanned page is one of them.

A test that was wrong about the format

It asserted that half a codestream is refused. It is not, and should not be: JPEG 2000 is progressive by construction, so a codestream cut short is a coarser picture of the same size — the opposite of a Flate stream cut short. A decoder that refused it would throw away a page every other reader shows. The test now says that, and a separate one says that something which merely opens like a codestream and continues into nonsense is still refused.

100% statement coverage, go vet and -race clean, nine cross-compile targets.

v0.11.0

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v0.10.0: — a stroke is one shape

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A stroke was rasterised a piece at a time and the pieces combined by keeping the greater coverage of each pixel. That is not a union: where two pieces meet along a shared edge each covers part of the pixel that edge cuts, and the greater of two halves is a half. A curve cut into thousands of short segments — how every plotting program writes one — came out at about half the colour it was asked for, combed through with a lighter notch at every vertex.

Every piece now goes into one edge list, wound the same way round, filled once under the nonzero rule. Round ends and corners are stepped polygons within a hundredth of a pixel of the circle; a round join draws only the outside of the turn, a round cap only the half past the end.

Filling now sweeps an index of the edges instead of asking every edge about every scanline:

	before	after
fill, 2000-sided polygon	9.29 ms	3.30 ms
stroke, 3000-segment curve, miter	2.82 ms	3.30 ms
stroke, 3000-segment curve, round	2.23 ms	3.27 ms

The stroke parity test compared against a reimplementation of the code being replaced, so it asserted the defect; it now compares against a definition — every point within half a width of the line — over 604 shape/width/clamp combinations.

Full details in #​18.

v0.9.0

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v0.8.0

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v0.7.0

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v0.6.0

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v0.5.1

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color: inlinable, allocation-light HSV/HSL/HWB conversions (#​9). Bit-identical fast paths (minMax3/absf, dropped no-op hue wrap, arithmetic Mod); inverse ~16% faster, zero-alloc unchanged. No API change.

v0.5.0

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v0.4.0

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v0.3.0

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v0.2.1

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v0.2.0

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