[Poppler-bugs] [Bug 78990] PDF Text hinting does not work for embedded otf fonts (CID Type 0C), does work for truetype.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78990

--- Comment #5 from Jerome <ce0c5679c447a438 at spamherelots.com> ---
> There is no such thing as identical hinting between CFF and glyf fonts.

Point taken. I'll rephrase to: They should render similarly enough so it 
doesn't appear as if one is black and the other regular at low zoom if
they render identically when zommed in.


> How did you generate the instructions for the glyf (aka ttf)? Fontforge?
> Ttfautohint?  By hand?

I've tried:
- straight otf->ttf via fontforge
- running ttfauthint on the ttf
- converting the results of ttfauthint back into otf via fontforge
- running authint from the adobe FDK on the otf.

and comapring against each other. It gets a little tricky (XeLatex 
and fontconfig have a will of their own) but so far the rendering is 
consistently different between otf and ttf, and so far it's by far
the dominating factor in the appearence of the rendered page.

> I see that the metrics are different.  Did you lose kerning?

You probably meant the faulty pdf. The answer is still: 
possibly, I didn't check (I'm a fontforge novice). 

Though kerning can affect color the difference in visual appearence looks to
me as being on the level of individual glyphs. 

Since the difference disappears when zooming in, I took that as a hint (pardon)
that the issue has to do with hinting, but perhaps it's something else
I'm unaware of.

The "mistaken" screenshot is actually quite close to the weight difference 
I'm seeing, even with the wrong fonts (still otf vs. ttf rendering).

>I expect a pdf viewer to disable all hinting for the rendered page.
>AFAIK evince follows that philosophy.  But if not, freetype added a new
>hinting engine in that last year, contributed by Adobe, which darkens
>glyphs at low resolutions.  Perhaps that explains what you see?

Using okular, I've disabled hinting (which does make a slight
visual difference) but the prononounced effect I described remains. 
otf is black ttf is regular.

Wouldn't you expect it to act similarly on both fonts? it's really
not a subtle visual difference I'm seeing.

> Or, the difference between how cubic and quadratic splines render might
> be noticible at those p/ex sizes.

You got me there. You're refering to a difference in how the glyph curves
are represented in each font format? Doesn't the fact that acrobat reader 
doesn't have this issue suggest otherwise? Is there a way to tell if it's
patented magic on behalf of adobe or a bug in poppler's rendering (or somewhere
else in the stack)?

I'm attached a new screenshot of the appearence of the pdf zoomed out
and close up taken from okular. evince looks much the same.

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