OpenSans font compatability

[GoogleCodeExporter]

It seems that the truetype package cannot load the OpenSans font.

The font is compatible with other TTF viewers/editors.. so I wonder why I 
receive this error (from freetype.ParseFont() function):

freetype: invalid TrueType format: bad kern table length

Download font at www.opensans.com, I used the OpenSans-Regular.ttf font, but it 
seems all the OpenSans fonts do not parse properly.

Best regards,
Stephen

Original issue reported on code.google.com by [email protected] on 26 May 2013 at 4:47

[boriwo]

Just ran into the same issue. Any plans to fix this in the near future?

[alimoeeny]

For me it opens Open-sans-regular but fails on many others (on a mac OSX 10.11, go 1.5.1 )

[jeffwilliams]

I'm having the same problem.

[artyom]

Here's a great explanation on what's wrong with Open Sans kerning table; its parsing indeed fails on this check:

        if 6*f.nKern != length-14 {
                return FormatError("bad kern table length")
        }

[narqo]

Same problem for me. Are there any plans to fix this?

[fstanis]

Any update? It seems to fail with Open Sans regular as well now.

[rillig]

A quick fix is to apply the following patch:

--- a/truetype/truetype.go
+++ b/truetype/truetype.go
@@ -345,7 +345,7 @@ func (f *Font) parseKern() error {
                return UnsupportedError(fmt.Sprintf("kern coverage: 0x%04x", coverage))
        }
        f.nKern, offset = int(u16(f.kern, offset)), offset+2
-       if 6*f.nKern != length-14 {
+	if uint16(6*f.nKern) != uint16(length-14) {
                return FormatError("bad kern table length")
        }
        return nil

This allows at least Calibri to be loaded successfully. I have no idea about other consequences, though.

[adnsv]

For some reason this problem is still not fixed in the main repo. This prevents lots of fonts from being used with this library.

The original freetype repo, would load such fonts. IMHO a bit incorrectly, but better than nothing.

Here is my version of a slightly more robust check:

	// For large kerning tables, the extracted length value may be incorrect.
	// For such fonts, often only the lower 16 bits of the actual length are
	// stored. Here we validate the lower 16 bits, and also make sure that
	// the extracted number of kerning pairs does not exceed the total length
	// of the kerning table.
	if uint16(6*f.nKern) != uint16(length-14) || 6*f.nKern > len(f.kern)-18 {
		return FormatError("bad kern table length")
	}

[guilhermehubner]

Hello! There is any updates on this? 🤔

[SamusAranX]

This is still an issue, btw

[montanaflynn]

Also hitting this with the the https://fonts.google.com/specimen/Anton downloaded ttf file.

[zwang]

Still an issue in 2021

[Vahanerevan]

+1

[dastanaron]

Still an issue in 2022

[rothcold]

Still have issue with Clear Sans

[SuperFromND]

This appears to still be an issue as of 2024; we just got a report about this over on the Ikemen GO repository (see ikemen-engine/Ikemen-GO#1715); it affects this font.

Is there any reason why the changes made in unidoc's fork or adnsv's fix above haven't been incorporated into the main branch?