963147 - Improve nsMathMLChar implementation with the Open Type MathVariants table

Status: NEW

(Core :: MathML, enhancement)

Description

[Frédéric Wang (:fredw)]

Bug 407059 will bring a first implementation based on the current nsMathMLChar code. When we move to MATH fonts, we can try to get even closer to the the Open Type MATH implementations. Some suggestions:

1) Drop the old *.properties table and only keep the nsOpenTypeTable structure. A generic Unicode table that follows the Open Type MATH format can be created.

2) Use AdvanceMeasurement for the variant instead of the ink metrics (may be more accurate)

3) Expose the ItalicsCorrection parameter for the glyph assembly and the italic correction for the size variant glyphs (bug 961482)

4) Use MinConnectorOverlap, StartConnectorLength, EndConnectorLength, FullAdvance, PartFlags to position and measure the glyph assembly more accurately.

5) Support an arbitrary number of components for a glyph assembly.

Comment 1

[Frédéric Wang (:fredw)]

I had the bad surprise to read on the Wikipedia article that Microsoft has patented some layout algorithms based on the OpenType MATH table:

https://en.wikipedia.org/wiki/OpenType#Math

So far, I assumed it was patent-free since it is implemented in various open source TeX engines.

Khaled, Jonathan: were you aware of that? Do you have more information? We should probably ask clarification to Microsoft...

As far as I know, the only new thing I implemented with respect to our previous implementation in bug 407059 is the "reverse" italic correction for large operators and the DisplayOperatorMinHeight value to select a variant for a display operator. But I suspect we won't be able to support the general MathVariants table algorithm described in

http://www.google.com/patents/US7242404
http://www.google.com/patents/US7453463

Comment 2

[Jonathan Kew [:jfkthame]]

(In reply to Frédéric Wang (:fredw) from comment #1)
> I had the bad surprise to read on the Wikipedia article that Microsoft has
> patented some layout algorithms based on the OpenType MATH table:
> 
> https://en.wikipedia.org/wiki/OpenType#Math
> 
> So far, I assumed it was patent-free since it is implemented in various open
> source TeX engines.
> 
> Khaled, Jonathan: were you aware of that? Do you have more information? We
> should probably ask clarification to Microsoft...

Rather, we should probably raise this with Mozilla's legal team. I don't know what our policy is with regard to such things.

In this particular case, as it's a familiar area, I'd probably have some thoughts on the validity (or otherwise) of such patents, but this may not be the best place for such a discussion.

Comment 3

[Khaled Hosny]

I have no idea about the presence of any patents whatsoever. No idea what to do either, so I’d be grateful to know the opinion of Mozilla's legal team on this.