Gio up

[sbinet]

Please take a look.

[sbinet]

this isn't the final answer: the new Gio API doesn't lend itself very nicely with our Push/Pop semantics. see 1 for more details.

(but we don't use explicitly Push/Pop in the vg/vggio tests. I'd expect plot/plotter.Field.Plot to fail)

also, it seems the latest Gio version has a somewhat different kerning algorithm.

[codecov-commenter]

Codecov Report

Patch coverage: 75.20% and project coverage change: +1.69 :tada:

Comparison is base (78cf2c9) 73.43% compared to head (10ff9ab) 75.13%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #764 +/- ## ========================================== + Coverage 73.43% 75.13% +1.69% ========================================== Files 56 58 +2 Lines 5176 7420 +2244 ========================================== + Hits 3801 5575 +1774 - Misses 1191 1649 +458 - Partials 184 196 +12 ``` | [Impacted Files](https://app.codecov.io/gh/gonum/plot/pull/764?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gonum) | Coverage Δ | | |---|---|---| | [vg/vggio/vggio.go](https://app.codecov.io/gh/gonum/plot/pull/764?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gonum#diff-dmcvdmdnaW8vdmdnaW8uZ28=) | `79.11% <72.97%> (ø)` | | | [vg/vggio/context.go](https://app.codecov.io/gh/gonum/plot/pull/764?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gonum#diff-dmcvdmdnaW8vY29udGV4dC5nbw==) | `100.00% <100.00%> (ø)` | | ... and [53 files with indirect coverage changes](https://app.codecov.io/gh/gonum/plot/pull/764/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gonum)

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[sbinet]

this needs https://lists.sr.ht/~eliasnaur/gio-patches/patches/40703

I haven't understood (yet?) why the embedded image is so blurry.

[sbinet]

I haven't understood the blur, but I know where it comes from: https://lists.sr.ht/~eliasnaur/gio/%3CCS8BHEBZ9GR5.NAXSHL22P0UG%40clrinfopc42%3E#%3CCSBMYF60V5V2.38PUCTE2N4NPI@clrinfopc42%3E

[sbinet]

so the blur comes from a different filtering algorithm used deep inside Gio. I guess we'll have to do the rescaling by hand CPU-side, with image/draw.

[sbinet]

well, this is the best I could come up with. still not on par with what we used to have though...

(I have tried different filters from x/image/draw. the NN is what looked best to my eyes. perhaps we should allow to optionally provide a way to use a user-provided x/image/draw.Scaler ?)

PTAL