[subset] Make it easier to keep evereything

[behdad]

Maybe add API on subset-input to keep everything. Basically this code:

harfbuzz/src/hb-subset-input.cc

Lines 485 to 503 in 52110f1

	const hb_subset_sets_t indices[] = {HB_SUBSET_SETS_UNICODE,
	HB_SUBSET_SETS_GLYPH_INDEX,
	HB_SUBSET_SETS_NAME_ID,
	HB_SUBSET_SETS_NAME_LANG_ID,
	HB_SUBSET_SETS_LAYOUT_FEATURE_TAG,
	HB_SUBSET_SETS_LAYOUT_SCRIPT_TAG};
	for (auto idx : hb_iter (indices))
	{
	hb_set_t *set = hb_subset_input_set (input, idx);
	hb_set_clear (set);
	hb_set_invert (set);
	}
	hb_subset_input_set_flags(input,
	HB_SUBSET_FLAGS_NOTDEF_OUTLINE |
	HB_SUBSET_FLAGS_GLYPH_NAMES |
	HB_SUBSET_FLAGS_RETAIN_GIDS |
	HB_SUBSET_FLAGS_NO_PRUNE_UNICODE_RANGES);

User can call this, then modify the input.

[behdad]

Would be a bit tricky to hook it up in hb-subset though, to let user override aspects after requesting to keep everything. Though maybe that works?

[behdad]

It works with hb-subset if one first adds --keep-everything then modifies glyphs / unicodes etc by subtracting from them for example.

[madig]

So if I keep_everything and then empty out the GID list, would it subset the font such that everything is kept, except glyphs that cannot be reached via cmap, composites or layout?

Edit: looking for the equivalent of

        # The subsetter configuration preserves all OT feature support.
        # It will remove unused, unencoded glyphs.
        subset_args_expert = [
            str(local_filepath),
            "--unicodes=*",
            "--no-ignore-missing-glyphs",
            "--notdef-outline",
            "--layout-features=*",
            "--name-IDs=*",
            "--name-languages=*",
            "--glyph-names",
            "--no-prune-unicode-ranges",
            "--recalc-bounds",
            f"--output-file={local_filepath_subset}",
        ]

[behdad]

So if I keep_everything and then empty out the GID list, would it subset the font such that everything is kept, except glyphs that cannot be reached via cmap, composites or layout?

Correct.

[yisibl]

@behdad For the --keep-everything option, the documentation does not specify its usage scenario.

If I just want to turn variable fonts into static fonts, should I use this option right?

e.g.

hb-subset VF.ttf -o subset.ttf --variations="wght=200" --keep-everything

[behdad]

If I just want to turn variable fonts into static fonts, should I use this option right?

Sounds about right, yes.