New option for handling ZWNJ in Arabic text rendering

Provide a new option 'arabic-shaper-ZWNJ-handling' that controls how
to display ZWNJ in Arabic text rendering (Bug#28339).
* lisp/language/misc-lang.el: Register arabic-shape-gstring in
composition-function-table.
(arabic-shaper-ZWNJ-handling): New variable.
(arabic-shape-log): New variable.
(arabic-shape-gstring): New function.
* lisp/composite.el (lgstring-remove-glyph): New function.

1 files changed, 14 insertions, 0 deletions

diff --git a/lisp/composite.el b/lisp/composite.el
index ab39e087e1f..72b0ffc8f48 100644
--- a/lisp/composite.el
+++ b/lisp/composite.el
@@ -442,8 +442,10 @@ after a sequence of character events."
 (defsubst lglyph-set-adjustment (glyph &optional xoff yoff wadjust)
   (aset glyph 9 (vector (or xoff 0) (or yoff 0) (or wadjust 0))))
 
+;; Return the shallow Copy of GLYPH.
 (defsubst lglyph-copy (glyph) (copy-sequence glyph))
 
+;; Insert GLYPH at the index IDX of GSTRING.
 (defun lgstring-insert-glyph (gstring idx glyph)
   (let ((nglyphs (lgstring-glyph-len gstring))
 	(i idx))
@@ -459,6 +461,18 @@ after a sequence of character events."
     (lgstring-set-glyph gstring i glyph)
     gstring))
 
+;; Remove glyph at IDX from GSTRING.
+(defun lgstring-remove-glyph (gstring idx)
+  (setq gstring (copy-sequence gstring))
+  (lgstring-set-id gstring nil)
+  (let ((len (length gstring)))
+    (setq idx (+ idx 3))
+    (while (< idx len)
+      (aset gstring (1- idx) (aref gstring idx))
+      (setq idx (1+ idx)))
+    (aset gstring (1- len) nil))
+  gstring)
+
 (defun compose-glyph-string (gstring from to)
   (let ((glyph (lgstring-glyph gstring from))
 	from-pos to-pos)