Re: [Devel] Artifacts in aliased font rendering - Email found in subject

[David Turner]

Hello,

Boris Letocha wrote:
> Hello,
>
> Ok, problem reproduced using:
> ftstring -m ABCDER -r 96 10 arial.ttf
> then switch off aa using "a" key. Patented hinting must be enabled. It does in 
> both 2.1.8 and current snapshots.
>
> for example: R looks like:
> #########
> #             ##
> #               #
> #               #
> #             ##
> #########
> #         ##
> #          #
> #           #
> #            #

Thanks for the example, I could spot the bug with it (even if my rendering is 
slightly
different from the graph above).

It was a bug in the TrueType glyph loader. More precisely, here's precisely what
happened:

  - the original (2.1.4) x/y scales computation in FT_Set_Char_Size did use
    rounding to compute the x_ppem and y_ppem. This corresponded to what the
    TrueType interpreter expected

  - we sinced changed the code in FT_Set_Char_Size to _not_ use rounding,
    but provided an "override" in the TrueType driver, and only this one,
    to re-compute the scales as needed (see Set_Char_Sizes in "ttdriver.c").
    the correct scales were stored in a TT_Size.metrics field, instead of
    the TT_Size.root.metrics

  - unfortunately, the glyph loader still used the TT_Size.root.metrics
    values, hence the artefacts.

Basically, we failed to update the glyph loader and do proper testing. It's
very strange but it seems that the problem was quite hard to spot anyway.

Please report, I've only tested the new code with Arial and Times :-)

Ahh. Feels good :-)

- David Turner
- The FreeType Project  (www.freetype.org)



> Thanks,
>
> Boris
>
> _______________________________________________
> Devel mailing list
> address@hidden
> http://www.freetype.org/mailman/listinfo/devel