Re: Pixel-perfect migration from ATSUI to Core Text
Re: Pixel-perfect migration from ATSUI to Core Text
- Subject: Re: Pixel-perfect migration from ATSUI to Core Text
- From: Quincey Morris <email@hidden>
- Date: Thu, 01 Sep 2016 13:34:55 -0700
- Feedback-id: 167118m:167118agrif8a:167118skybuBSQI_:SMTPCORP
On Sep 1, 2016, at 10:53 , Andreas Falkenhahn <email@hidden> wrote:
>
> Who said that the answer was clearly "no”?
Me. And you. You took a trivially simple single-character example, and failed to come up with the same answer.
> So far these attempts haven’t been successful but …
You *might* find a combination of settings that brings success in your test cases, but that’s just fixing the test when you know the answer.
> When rendering the text using ATSUDrawText()
> and CTLineDraw(), the pixels match *exactly*. There is not a single difference,
> it is exactly the same, pixel by pixel.
It’s hardly surprising this would be true some, even most, of the time. But are you sure that there was no bug or deficiency in ATSUI code that Apple fixed in CoreText? No bug in font file metrics or font hinting that has been fixed in 10 years of font updates?
> That's why I am of the opinion that
> it should also be possible to achieve an identical look when drawing strings
> glyph by glyph and manually calculating the advance.
No, absolutely not, and that’s my real point. Line layout *uses* individual glyph advance widths, but the effective advance width of glyphs within in a line of text is contextually dependent, computed using other factors, some of which are in practical terms not predictable.
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