Using fonts from MathJax's CDN for Native MathML

[fred-wang]

Firefox 15 is going to be release today and could now use MathJax fonts for the MathML operators.

See https://groups.google.com/forum/?fromgroups=#!topic/mathjax-dev/9EyiDt_0ess

=> assigned to myself.

[fred-wang]

I haven't test the fix yet.

(this time I combined and repacked MathJax, although I don't know if that's convenient for merging branch)

[fred-wang]

There were extra single quotes in the CSS rules, that I have fixed in my latest commit. I tested this with Firefox Beta 15 and the Web fonts are correctly used:

http://devel.mathjax.org/testing/mathjax/tests/MozillaTortureTest/texvsmml.html

However, MathJax does not seem to scale correctly the math with respect to the surrounding text. I guess this is because it does not have access to the font metrics until the fonts are downloaded...

[dpvc]

Yes, I think you have touched on the issue. The way MathJax tries to match the size is to use a box of a particular height and width in ex's and measure the size of that box. I guess that the web fonts aren't loaded by that action, and even if they were, they might not have arrived yet, so MathJax gets the wrong size. I suppose I could have MathJax insert a dummy <math> element that would force the font to load, and wait a bit before starting to measure things, but MathJax would not know how long to wait. (That is why MathJax's font detection algorithm is so crucial to its own use of the fonts.)

[fred-wang]

Do you think that scaling the math with respect to the surrounding text is the only place where MathJax needs the fonts to be available? I'm wondering if it's really worth addressing this issue now (it is less serious than the bad rendering when users do not have the fonts installed).

Another solution would be to insert the math elements to let Firefox display them, wait a certain delay and render the math elements again. Note sure that would be better, though.

[dpvc]

I think you are probably right, it is not something to worry about at the moment, so I'm marking it ADDRESS LATER so we remember to come back to it for the release after this one.

[fred-wang]

I meant, we can take the fix at it is now (allowing the user to get a decent rendering without fonts installed) even if the scale is not applied correctly.

[dpvc]

Sorry, I'm working on too many things at once, and was getting confused about the plain FF usage of the fonts versus the MathJax NativeMML usage. Yes, we should be able to go ahead with the changes. It would also be possible, I suppose, to use a tester like the HTML-CSS output does to find out if the fonts are ready. The problem is, MathJax doesn't know what fonts the native MathML renderer will actually be using, so that probably doesn't help.

I also noticed that the width of the math can grow when the fonts arrive, so the space reserved for the math may be too small in the end. That is potentially a worse situation. I suppose MathJax could go back afterward and adjust the sizes after it is finished.

[fred-wang]

The problem is, MathJax doesn't know what fonts the native MathML renderer will actually be using, so that probably doesn't help.

I think we should add options similar to the HTML-CSS / SVG outputs to force the choice of a font. We can add font-family rules to change the font of the text and the other -moz-* rules for the stretchy symbols.

I also noticed that the width of the math can grow when the fonts arrive, so the space reserved for the math may be too small in the end. That is potentially a worse situation. I suppose MathJax could go back afterward and adjust the sizes after it is finished.

Yes, I also noticed that too, although I was not sure it was the same problem or not. IIRC this was to fix a bug when the math is zoom.

Anyway, I think your are right that we should handle this for after the next release.

[dpvc]

There is a font menu (hidden by default) that controls the HTML-CSS font usage. We could probably do a similar one for NativeMML output.

[fred-wang]

I was thinking to the configuration options, but probably a font menu would be a good idea too.

[dpvc]

OK, good point. Yes, font options in the configuration for NativeMML would be appropriate.

[fred-wang]

I've updated my branch to make the NativeMML font configurable. For the moment, I didn't do font detection or take the menu choice into account.

It seems that the font detection and verification is not so simple. Would it be best to move it to a separate file that would be shared between the HTML-CSS & NativeMML output? I guess just force a reflow after some arbitrary time to avoid the problem mentioned above, but that won't help to detect which local fonts is installed.

[fred-wang]

I wanted to put the FONTTEST variable in a specific extension that would be loaded by the HTML-CSS & NativeMML outputs but then I realized that it uses the HTMLCSS variable and specifically the HTMLCSS.FONTDATA. Is there a simple and reliable way to detect when the Web fonts arrive, that could be put in the NativeMML jax instead? It's a shame that browsers don't have an API to do that...

[dpvc]

The font testing is one of the most fragile components of MathJax, so "simple and reliable" is not really what I would call it. If you are wanting to deal only with the MathJax fonts, then the code could probably be simplified, and the section of HTMLCSS.FONTDATA that is needed (not much as I recall) could be included. But doing the detection in general is quite hard.

It might be worth looking at the google webfont code to see if they have developed anything better.