Re: [ft-devel] GSoC - Image comparison in test framework

[Arvinder Bhathal]

> You can completely ignore kerning issues.  The primitive kerning data
> derived from the `kern' table is not worth for further investigation
> IMHO (besides probably monitoring the values itself), and the more
> complicated kerning from the `GPOS' table isn't handled by FreeType at
> all but by higher-level libraries like HarfBuzz or ICU.

> If you ignore kerning, the only reason for different gaps are changed
> left and right side bearing values, and this is covered by the advance
> width.  So it is necessary to monitor both the scaled and linear
> advance width values (the latter can be changed by variation font
> instances).

I see. I'm going to continue looking at the source to understand the
specifics involved in monitoring these values.

> Yes, but what's needed is a solution to nicely visualize the
> differences.

Do we want to detect and highlight the location of the
error/difference in a particular glyph? For example, a pixel is
missing at the bottom of a character so we identify that area as
containing the difference, and somehow show this in the report. If a
stem were shifted, I imagine the entire glyph might be identified as
being different. Or, we just display the baseline and the erroneous
glyph without trying to identify where within the glyph the error was.
The measure of the difference between baseline and test would be the
same in either case.

Also, are we targeting a specific version of HTML for the output
report? HTML 4.01 should be compatible enough, although nowadays HTML
5 might also be okay.


Regards,

Arvinder