This post includes a solution of the problem
The Hebrew-Culmus font is complicated so I downloaded some free Hebrew fonts including Horev CLM Heavy:
https://www.hbrewfont.net/download.php?id=737273
This font does not use sixty or a dozen kerning tables, but only one, which makes it easy to analyze. As a result, I was able to implement a kerning table for the glyphs from the Hebrew Unicode section. In this post, I show you how to solve this problem with FontForge.
1.
First, you should go to the Hebrew Unicode section and rename the available glyphs except geresh and gershayim. To do this, highlight the glyph, use the right mouse button, run the Glyph Info... option and in the Glyph Name item use the scrolling list and select a PostScript name starting with afii..., e.g. afii57664 for aleph. Repeat this process for all Hebrew letters.
2.
Go to the Element | Font Info... window, select the Lookups option, select the GPOS tab, and use the Add Lookup button. In the Lookup Name box, type something like kerning-rtl.
Then go to the top of this window and select Pair Position (kerning) option from the Type list.
Then, under the Feature column, click the down arrow next to New and select kern Horizontal Kerning. As a result, kern appears in the left column and DFLT{dflt} latn{dflt} hebr{dflt} appears the right column.
Click the down arrow next to that string, and select and then delete positions DFLT | dflt and latn | dflt. As a result, you stay in hebr | dflt only.
Finally, select Right To Left and Ignore Combining Marks options in the Lookup window.
As a result, you get a kerning-rtl lookup on the GPOS tab. When it is highlighted, click the Add Subtable button and accept the name kerning-rtl-1.
At this point, the Kerning format window appears. I have not use it so you can click OK.
3.
As a result, the Lookup Subtable, kerning-rtl-1 window will appear. This is where you kern the Hebrew letters from the Unicode section.
The table has four columns: 1) First Glyph Name; 2) Second Glyph Name; 3) Δx #1, and 4) Δx_adv #1.
1) and 2) apply to consecutive pairs of glyphs, but remember that in this case we are prepare kerning to write from right to left, so the first character is displayed below to the right of the second character.
3) and 4) relate to the kerning value: in this case you will use the same values for both of them. The first sets the kerning between the selected characters, the second matches the kerning before the first character, since this kerning for right-to-left writing works from left to right.
Right now you have afii57664 (aleph) in the First Glyph Name and Second Glyph Name columns, and the Δx #1 and Δx_adv #1 columns have the same value as –286.
When I set the kern to 319 pair of Hebrew letters, FontForge only guessed the correct once. So these suggested values are a hindrance rather than a help.
After kerning is set to aleph-aleph, you need to move on to the next letters.
For the Paleo-Hebrew Abjad font, I have three classes of characters: 1) Hebrew letters with names afii57664 to afii57690; 2) geresh and gershayim named uni05F3 and uni05F4; and the period named period.
To set kerning for a pair of letters such as aleph-geresh, click the New position, when you are in the first column enter the letter a and select afii57664 from the list, when in the second column enter the letter u and select uni05F3 from the list, finally set the same kerning in the next two columns.
4.
Since I had kerned all the Paleo-Hebrew letters from the ASCII section beforehand, I ran a separate FontForge instance and opened the Kern Pairs window using the View | Combinations | Kern Pairs option. I used the information in this window to clone an already defined kerning.
So I copied the kerning for letter pairs from the ASCII section to the letter pairs of the Hebrew Unicode section.
The first item in the Kern Pairs screenshot is kerning for the apostrophe-aleph character pair. In the Hebrew Unicode section, the apostrophe becomes geresh.
In the Lookup Subtable, kerning-rtl-1 window screenshot the highlighted pair is aleph-geresh (read right to left).
Correct kerning for apostrophe-aleph from ASCII section is valid for aleph-geresh from Hebrew Unicode section.
So, if you set kerning for an ASCII section, you have to read consecutive entries from right to left to find the correct kerning for letter pairs from the Hebrew Unicode section.
[EDITED]
If you exit the Lookup Subtable, kerning-rtl-1 window, which is recommended for saving partial work, you can reopen it using the Element | Font Info... menu and selecting the Lookups | GPOS | kerning-rtl | kerning-rtl-1 position. Then click the Edit Data button.
* * *
In the previous post I mentioned that I am letting you know here when I release the Paleo-Hebrew Abjad font. And so I do.
I am working on it right now. The last night I prepared a Hebrew keyboard map for Linux and added a macro to the README file that flips the text from left to right to right to left.
I can not guess my next ideas. To be sure I am finished, at least 24 hours have to pass without changes to the files from the Paleo-Hebrew Abjad package. So be patient.
