What is the correct way to create OTC/TTC with theirs tables shared

[TakWolf]

I am not sure if the following codes is correct (or recommended), I only infer them through existing APIs:

def create_xtf(name, is_ttf: bool):
   builder = FontBuilder(units_per_em, isTTF=is_ttf)
  # Some build codes
  return builder.font


ttc = TTCollection()
ttc.fonts.append(create_xtf('my font 1', true))
ttc.fonts.append(create_xtf('my font 2', true))
ttc.fonts.append(create_xtf('my font 3', true))
ttc.save('my-font.ttc', shareTable=True)

I did successfully create a ttc file. But it seems that the table is not shared. What did I do wrong？

[justvanrossum]

I was going to suggest this:

ttc = TTCollection(shareTables=True)

but it seems that only has effect when reading a TTC.

[justvanrossum]

I tried to reproduce with a simple script, but it seems to correctly share identical tables:
build_ttc.py.zip

[justvanrossum]

Can you post a (link to a) TTC binary that you built that isn't sharing tables?

[TakWolf]

Yes, let me do some organizing

[justvanrossum]

Btw. if even a single glyph is different, then the table containing the glyph data cannot be shared.

In that case it may help to include the exact same glyph set in all fonts, but build different cmaps for each.

[TakWolf]

In that case it may help to include the exact same glyph set in all fonts, but build different cmaps for each.

I overlooked this. Let me check it.

[TakWolf]

Still invalid.

example-fonts.zip

These two font created by this script: https://github.com/TakWolf/pixel-font-builder/blob/master/examples/demo.py

https://github.com/TakWolf/pixel-font-builder/blob/master/examples/demo.py#L167C1-L171C71

I merged otf 1000 times, only with different family names.

The remaining issue is that I won't decide is that should tables object are required the same memory objects?

[TakWolf]

Should the fonts use the same memory objects for the tables, only then can be shared?
I don't see that your example requires the same memory object

[justvanrossum]

The data for the table to be shared needs to be identical before it can be shared. It does not need to be the same memory object, but the have to compare equal.

I now see what's going on: the font name is included in the CFF table, too, so it is the name that makes the CFF table not sharable in your case :(

Perhaps you can try passing the same data to setupCFF() in all cases, and only make differences in the name table.

[punchcutter]

The way Source Han does this is by pulling the CFF table from the default Japanese font and inserting it into all the others.