bugThe FreeType Project - Bugs: bug #54371, Do varfont interpolation in floats

 
 

bug #54371: Do varfont interpolation in floats

Submitted by:  Behdad Esfahbod <behdad>
Submitted on:  Wed 25 Jul 2018 04:20:01 AM UTC  
 
Severity:  3 - Normal Item Group:  None
Status:  None Privacy:  Public
Assigned to:  None Open/Closed:  Open
Planned Release:  None

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Thu 01 Nov 2018 06:03:05 PM UTC, comment #8:

On modern high-end displays 200 ppem becomes a normal half-inch title size, with the quantum of stem width of 200/2048 = 6/64 of a pixel. This is still a hardly noticeable quantum of brightness.

I guess I cannot visualize how the problem would manifest itself.

Alexei Podtelezhnikov <podtelez>
Project Member
Thu 01 Nov 2018 05:10:27 PM UTC, comment #7:

I mean, that's one way to address the issue.

Behdad Esfahbod <behdad>
Thu 01 Nov 2018 05:09:40 PM UTC, comment #6:

> Are you suggesting that the interpolation be done in device pixel (1/64) units instead of FUnits?


Yes.

Behdad Esfahbod <behdad>
Thu 01 Nov 2018 05:06:37 PM UTC, comment #5:

Behdad, I still do not follow, sorry.

We seem to be using FT_Fixed for all delta/multiplier calculations, which should certainly be enough. I do not see any rounding up.

Are you suggesting that the interpolation be done in device pixel (1/64) units instead of FUnits?

Alexei Podtelezhnikov <podtelez>
Project Member
Thu 01 Nov 2018 05:51:20 AM UTC, comment #4:

My request is simple.

Variable fonts are declared as a base font and multiple deltas. The final font is a (convex) linear interpolation of these. Ie. the master font plus sum of (delta*multiplier). The multipliers are numbers between (inclusive) 0 and 1.

Currently, each (delta*multiplier) is rounded up. This results in too much error, as well as quantizing the possible instances unncessarily.

No, I don't think this has to do with axis granularity.

Behdad Esfahbod <behdad>
Thu 01 Nov 2018 04:18:59 AM UTC, comment #3:

I was just inviting you to explain the bug better...

Ultimately though, isn’t it a font problem if the axis is not granular enough?

Alexei Podtelezhnikov <podtelez>
Project Member
Thu 01 Nov 2018 02:18:15 AM UTC, comment #2:

Link, or summary, or something?

Behdad Esfahbod <behdad>
Thu 01 Nov 2018 02:06:17 AM UTC, comment #1:

I do not know what exactly you are complaining about but I committed some optimizations, which might help.

Alexei Podtelezhnikov <podtelez>
Project Member
Wed 25 Jul 2018 04:20:01 AM UTC, original submission:

By limiting interpolation output to whole FUnits, we are basically limiting the stem-width to whole FUnits. When you think about the kind of hairline fonts people are designing with varfonts now, and rendered at high-DPI, or large sizes that such hairlines will be useful, I think supporting fractional stem widths is worthwhile.

Behdad Esfahbod <behdad>

 

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