All platforms use same code to remove context-dependent codepoints from text input.

This commit introduces function fl_utf8_remove_context_dependent() that removes
from an UTF-8 string its context-dependent codepoints. Platforms macOS, Wayland
and X11 call this function to process UTF-8 text received from a character palette
as input to FLTK text. This makes sure FLTK text-editing widgets process textual input
equally and consistently across platforms, especially emojis entered via a palette.

Platform Windows creates a series of separate system events to input an emoji
via the character palette. For this reason, function fl_utf8_remove_context_dependent()
is not used by this platform which does internally the same filtering of context-
dependent codepoints.

1 files changed, 28 insertions, 1 deletions

diff --git a/src/fl_utf8.cxx b/src/fl_utf8.cxx
index 7cc53f13b..05e45ded3 100644
--- a/src/fl_utf8.cxx
+++ b/src/fl_utf8.cxx
@@ -3,7 +3,7 @@
 //
 // Author: Jean-Marc Lienher ( http://oksid.ch )
 // Copyright 2000-2010 by O'ksi'D.
-// Copyright 2016-2022 by Bill Spitzak and others.
+// Copyright 2016-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -1630,3 +1630,30 @@ unsigned fl_utf8from_mb(char* dst, unsigned dstlen, const char* src, unsigned sr
 }
 
 /** @} */
+
+#ifndef FL_DOXYGEN
+
+/* This function removes from an UTF-8 string its context-dependent codepoints
+ when there are any, and returns the length of the possibly shortened string.
+ */
+int fl_utf8_remove_context_dependent(char *text, int len) {
+  if (len > 1 && fl_utf_nb_char((const uchar*)text, len) > 1) {
+    // Some emojis are expressed by a series of Unicode points
+    char *p = text, *end = text + len;
+    while (p < end) { // loop over all unicode points of the series
+      int l_point;
+      unsigned u = fl_utf8decode(p, end, &l_point); // extract one such unicode point
+      if ((u >= 0xFE00 && u <= 0xFE0F)      // variation selectors
+          || u == 0x200D                    // zero-width joiner
+          || (u >= 0x1F3FB && u <= 0x1F3FF) // EMOJI MODIFIERS FITZPATRICK TYPE
+          ) { // remove context-dependent unicode points
+        memmove((void*)p, p + l_point, (end - (p+l_point)) + 1);
+        end -= l_point;
+        len -= l_point;
+      } else p += l_point; // keep other unicode points
+    }
+  }
+  return len;
+}
+
+#endif // ! FL_DOXYGEN