bugThe FreeType Project - Bugs: bug #54969, Document FT_Face_Rec_::bbox as...


bug #54969: Document FT_Face_Rec_::bbox as unreliable / deprecated.

Submitted by:  bungeman <bungeman>
Submitted on:  Tue 06 Nov 2018 03:44:29 PM UTC  
Severity:  3 - Normal Item Group:  None
Status:  None Privacy:  Public
Assigned to:  None Open/Closed:  Open
Planned Release:  None

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Sat 06 Apr 2019 05:11:49 AM UTC, comment #2: 


Werner LEMBERG <wl>
Project Administrator
Tue 06 Nov 2018 04:22:08 PM UTC, comment #1: 

Ben, since you are a native speaker, can you prepare a patch?

Werner LEMBERG <wl>
Project Administrator
Tue 06 Nov 2018 03:44:29 PM UTC, original submission:  

As pointed out in the Note in the section https://docs.microsoft.com/en-us/typography/opentype/spec/otvaroverview#variation-data-tables-and-miscellaneous-requirements

"... the xMin, yMin, xMax, yMax, macStyle and lowestRecPPEM fields in the font header ('head') table are not supported by variation data and should only be used in relation to the default instance for the font. Also, variations for values in the kerning ('kern') table are not supported; variable fonts should handle kerning using the GPOS table."

Unfortunately, this means that there is no longer any reliable 'fast union of all glyph bounds'  available in an OpenType font. As a result, any user of these values may get very unexpected results if they are relying on this bbox having a sensible value.

Obviously, this field cannot be removed or given bad values for now, but this should be noted so this field isn't carried over into a future FreeType 3 and so existing users know its limitations (can't be used a a generic fast bounding box for quick rejection).

bungeman <bungeman>


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