Issue with application of OpenType features

[yanone]

Hi,

I’m having issues applying OpenType features to text in a PDF.
I’ve rewritten my own renderer to write original drawBot code so I can test it in the main DrawBot.app to rule out problems with my own code.

For instance, the sups feature doesn’t apply.
I’ve collected the files to test here.
The example with the sups feature is in line 408 (result shows on page 3 in the PDF).
The feature gets turned on beforehand and turned off afterwards. I found this to cause less confusion in the rendering than explicitly setting all available features at once.

What puzzles me:
If I reduce the code to just the necessary lines to render that text with the sups feature, it renders fine (never mind that the feature isn’t written professionally yet, as in all the glyphs in the example would get replaced at the moment, not contextually...).
That means that somewhere along the way someone got confused with the commands to the point where features don’t get applied properly anymore.

So this works, which is exactly the same code, only much less:

import os

newPage(595.275590551, 841.88976378)
installFont(os.path.join(os.path.dirname(__file__), 'NonameSans-Regular.otf'))
installFont(os.path.join(os.path.dirname(__file__), 'NonameSans-Bold.otf'))

########################

cmykFill(0.0, 0.0, 0.0, 1.0, 1.0)
stroke(None)
strokeWidth(None)
lineHeight(28.8)

font('NonameSans-Bold')
fontSize(24)
language(None)
textBox(u'''120m2''', (255.118110236, 501.732283465, 141.732283465, 56.6929133858), align = 'center')

########################

fill(1.0, 0.411764705882, 0.490196078431, 1.0)
stroke(None)
strokeWidth(None)
lineHeight(24.0)

font('NonameSans-Regular')
fontSize(20)
language(None)
textBox(u'''→''', (396.850393701, 527.811023622, 28.3464566929, 28.3464566929), align = 'center')

########################

cmykFill(0.0, 0.0, 0.0, 1.0, 1.0)
stroke(None)
strokeWidth(None)
lineHeight(28.8)

font('NonameSans-Bold')
fontSize(24)
openTypeFeatures(sups=True)
language(None)
textBox(u'''120m2''', (425.196850394, 501.732283465, 141.732283465, 56.6929133858), align = 'center')
openTypeFeatures(sups=False)

[justvanrossum]

It would be nice if you could reduce the failing code to something as small as possible.

[yanone]

I know, but that’s where it gets complicated.
The complete file in the download link in the OP wouldn’t produce the expected result, for instance in line 408.
But as soon as I reduce the code (attempt made also in OP), it suddenly works as expected.
:/

[justvanrossum]

For me it is currently just too much and too complex to deal with. Try to change/remove small things at a time and try to zoom into the moment when it goes from "not working" to "working".

[yanone]

Right, I just understood myself what you meant by that. I'll do that and get back.

[yanone]

Okay, I found it. Just not really sure what to make of it.

This code works:

import os

newPage(595.275590551, 841.88976378)
fontName = installFont(os.path.join(os.path.dirname(__file__), 'NonameSans-Bold.otf'))
font(fontName)
fontSize(24)

########################

openTypeFeatures(sinf=True)
textBox(u'''C20H25N3O''', (425.196850394, 558.42519685, 141.732283465, 56.6929133858), align = 'center')
openTypeFeatures(sinf=False)

########################

openTypeFeatures(sups=True)
textBox(u'''120m2''', (425.196850394, 501.732283465, 141.732283465, 56.6929133858), align = 'center')
openTypeFeatures(sups=False)

With the sinf feature for the first textBox() both lines work, with subs instead of sinf (like in my previous code) neither work. I’ve also tried that with Adobe fonts to the same result.
I’m guessing that it goes back to the CoreText implementation of the OpenType features and doesn’t really have anything to do with DrawBot. Quite some pitfalls here with Apple’s implementation. They even implement features which aren’t in the font.

Thanks for pointing out how to find the problem and sorry for bothering.

So here’s another insider question: One could use compositor for compositing the features as it seems to be completely standard-compliant. Could one print glyphs into PDFs with DrawBot that aren’t encoded, as real text and not Bezier paths?

[justvanrossum]

Thanks, that's a great reduction. There's indeed something fishy here, and it may well be a DB bug.

[yanone]

Okay, if you put it that way, here’s another one that I didn’t mention yet:

A second sample that didn’t work for me was the ordn feature.
So the in the below code the third textBox() only shows the correct ordn substitution if sups lines are commented out. Once they’re in, the ordn breaks.

import os

newPage(595.275590551, 841.88976378)
installFont(os.path.join(os.path.dirname(__file__), 'NonameSans-Bold.otf'))
font('NonameSans-Bold')
fontSize(24)

########################

openTypeFeatures(sinf=True)
textBox(u'''C20H25N3O''', (425.196850394, 558.42519685, 141.732283465, 56.6929133858), align = 'center')
openTypeFeatures(sinf=False)

########################

#openTypeFeatures(sups=True)
textBox(u'''120m2''', (425.196850394, 501.732283465, 141.732283465, 56.6929133858), align = 'center')
#openTypeFeatures(sups=False)

########################

openTypeFeatures(ordn=True)
textBox(u'''1a 2o''', (425.196850394, 388.346456693, 141.732283465, 56.6929133858), align = 'center')
openTypeFeatures(ordn=False)

[justvanrossum]

Btw. font() and friends also take a path to a font file, so you don't have to use installFont().

[justvanrossum]

There seems to be a weird interaction between these features. @typemytype, can you have a look when you have time?

[typemytype]

weird interaction!! will have a look

[typemytype]

setting openTypeFeatures(None) helps as this clears the whole stack of openTypeFeatures.

somehow the off attribute in coreText is not correct https://github.com/typemytype/drawbot/blob/master/drawBot/context/tools/openType.py#L438

(if got this map from @behdad 's harfbuzz see https://github.com/behdad/harfbuzz/blob/master/src/hb-coretext.cc#L445)

[yanone]

Indeed, the openTypeFeatures(None) solved my issue. Thanks for taking the time.

Right, the kNormalPositionSelector attribute shows up for exactly all the features that I had problems with.

I’ll leave the issue open in case you want to get back to changing the attributes.
Otherwise, thanks again and see you here or elsewhere :)

[behdad]

Anything I need to fix? I got the table from Apple...

[typemytype]

@behdad this is a drawBot issue, I guess

The order of features toggled on and off are taken from a dict and it happens when the openTypeFeature dict is something like dict(sups=True, sinf=False)

as dict keys are not ordered drawBot could first set the feature tag for sinf and then set the sups back to kNormalPositionSelector

Im hoping sorting the openTypeFeature dict by value False first would solve this.

[typemytype]

should be fixed here: 853d42f

[yanone]

I can confirm that the features get applied correctly now without resetting them using openTypeFeatures(None).
So I’m closing this issue. Thank you.

[typemytype]

well the fix should apply the features correctly by disabling the feature with "sups"=False

[yanone]

Yes, it does.

[typemytype]

thanks! oef