[cairo] rounding glyph positions

[Matthias Clasen]

On Fri, Aug 2, 2019 at 10:21 AM Uli Schlachter <psychon at znc.in> wrote:

> Hi,
>
> On 01.08.19 23:00, Matthias Clasen wrote:
> > But I'd still like to understand what the rationale is for a) this being
> > separate from hint metrics
> > and b) this not being settable.
>
> the rationale basically is "the test suite's reference images are
> correct by definition, so how can we make cairo generate this output"?
> According to "git blame", I introduced this option back when I still
> tried to sort out the mess that is the test suite:
>
> commit cee1dadc66107e1cc6bcac7718e0b67969141876
> Author: Uli Schlachter <psychon at znc.in>
> Date:   Thu Oct 21 22:14:57 2010 +0200
>
>     Other backends: Set round_glyph_positions to OFF
>
>     This sets CAIRO_ROUND_GLYPH_POS_OFF in all surface backends that
> didn't use
>     CAIRO_ROUND_GLYPH_POS_ON.
>
>     Signed-off-by: Uli Schlachter <psychon at znc.in>
>
> commit d24e9881de7b392cfce1d82c9861553ece558aaf
> Author: Uli Schlachter <psychon at znc.in>
> Date:   Thu Oct 21 14:03:38 2010 +0200
>
>     raster backends: Set round_glpyh_positions to ON
>
>     This fixes "text-rotate" in the test suite for the image backend and
>     "overlapping-glyphs" for the xcb backend.
>
>     Signed-off-by: Uli Schlachter <psychon at znc.in>
>
> commit b514863a0ee8e6c4f0a994f6f5e7db18ce290e79
> Author: Uli Schlachter <psychon at znc.in>
> Date:   Thu Oct 21 13:59:25 2010 +0200
>
>     Actually implement round_glpyh_positions
>
>     The previous commit only added this option and made sure it gets
> set, but it
>     didn't actually have any effect. This commit now implements this
> option.
>
>     Signed-off-by: Uli Schlachter <psychon at znc.in>
>
> commit 6bfe71124b56b496056b77b3b51eef4d656ccf54
> Author: Uli Schlachter <psychon at znc.in>
> Date:   Thu Oct 21 13:52:33 2010 +0200
>
>     font options: Add private round_glpyh_positions field
>
>     Signed-off-by: Uli Schlachter <psychon at znc.in>
>
> Looking at the git history for the reference images... I am not quite
> sure where it came from. Back in 2010, I was assuming that the reference
> images are correct, I guess. Since then, I saw others fixing test
> failures by just declaring the current cairo output as the reference. I
> never tried to do that since I do not what each test actually really
> tests and if the difference that makes the test fail is a bug or not.
>
> What to do with this information... well, I do not know. If you want,
> you can revert the above four commits, but I would hope that this does
> not regress the test suite (= some higher power has to declare that the
> current reference images are wrong and the new output is correct and
> should be the new reference image).
>
>
>
I might suggest to simply reuse hint-metrics for this purpose, based
on the theory that if you don't want hinted metrics, you probably don't
want rounded glyph positions either.
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