Text rendering problem using OpenType font and cursive lookups with mixed RIGHT_TO_LEFT flag

Question

amindk OP

Created Sep ’25

Replies 1

Boosts 1

Participants 1

Hi,

I am developing an OpenType font with the following cursive feature.

feature curs {  
  lookup cursivejoinrtl;  # RIGHT_TO_LEFT flag set between Hah, Meem, Yeh and final Meem
  lookup rehwawcursive; # RIGHT_TO_LEFT flag clear between Waw and Hah
} curs;

Here is the rendering of the word وحميم in TextEdit.

Using HarfBuzz I got the following result.

Screenshot on 2024-08-20 at 18.49.01.png

The same rendering problem occurs when using Safari. It seems that is related to Core Text.

I reported the issue to Feedback Assistant over a year ago but haven't had a response yet. So I'm posting the problem on this forum.

Any support on this matter would be greatly appreciated.

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Answer 1

amindk OP

1w

The issue arises even when there are two disjoint cursive segments.

To isolate what is happening, I reduced the cursive lookups to only the two following lookups.

lookup coretexttest_rtl_clear {
  lookupflag IgnoreMarks;
  pos cursive waw.isol <anchor NULL> <anchor 0 300> ;
  pos cursive smallalef.isol  <anchor 0 0 > <anchor NULL>;	
} coretexttest_rtl_clear;
lookup coretexttest_rtl_set {	
  lookupflag IgnoreMarks RightToLeft;
  pos cursive behshape.init <anchor NULL> <anchor 0 0> ;
  pos cursive lam.fina  <anchor 545 0 > <anchor NULL>;	
} coretexttest_rtl_set;
feature curs {
  lookup coretexttest_rtl_set;
  lookup coretexttest_rtl_clear;
} curs;

Below is the result of shaping the word “وَٰبل” in Safari 26.1.

Screenshot 2025-11-19 at 14.24.15.png

The Beh sits higher than expected and does not visually align with Lam, even though there is no cursive positioning defined between the Alef and the Beh.

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