From a0c2219de0d042e9978a59e75195eb46d96bc5e2 Mon Sep 17 00:00:00 2001
From: alektron <alektron1@gmail.com>
Date: Sat, 10 Aug 2024 15:39:32 +0200
Subject: [PATCH 1/2] =?UTF-8?q?Fix:=20utf8=5Fdecode=20fails=20for=20certai?=
 =?UTF-8?q?n=2016=20bit=20multibyte=20sequences=20e.g.=20when=20typing=20a?=
 =?UTF-8?q?=20'=C3=9C';?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 src/base/base_strings.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/base/base_strings.c b/src/base/base_strings.c
index 91a47562f..14a4c27e2 100644
--- a/src/base/base_strings.c
+++ b/src/base/base_strings.c
@@ -1228,7 +1228,7 @@ utf8_decode(U8 *str, U64 max){
     }break;
     case 2:
     {
-      if (2 < max)
+      if (1 < max)
       {
         U8 cont_byte = str[1];
         if (utf8_class[cont_byte >> 3] == 0)

From e7b2f27a2a44a70d813f9a7b9336b920bdeb54a4 Mon Sep 17 00:00:00 2001
From: alektron <alektron1@gmail.com>
Date: Sat, 10 Aug 2024 15:40:45 +0200
Subject: [PATCH 2/2] UI_EventDeltaUnit_Char now accounts for UTF8 multi byte
 sequence;

---
 src/ui/ui_core.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/src/ui/ui_core.c b/src/ui/ui_core.c
index d2b79b831..7010d4e8a 100644
--- a/src/ui/ui_core.c
+++ b/src/ui/ui_core.c
@@ -175,8 +175,35 @@ ui_single_line_txt_op_from_event(Arena *arena, UI_Event *event, String8 string,
     default:{}break;
     case UI_EventDeltaUnit_Char:
     {
-      // TODO(rjf): this should account for multi-byte characters in UTF-8... for now, just assume ASCII and
-      // no-op
+      if (delta.x > 0)
+      {
+        UnicodeDecode decode = utf8_decode(string.str + cursor.column - 1, string.size);
+        delta.x = decode.inc;
+      }
+      else
+      {
+        //Backwards check/count for UTF-8 multi byte sequence
+        U32 numSeqBytes = 0;
+        for (S64 idx = cursor.column - 2; idx >= 0; idx -= 1)
+        {
+          B32 isSeqByte = ExtractBit(string.str[idx], 7) == 1 && ExtractBit(string.str[idx], 6) == 0;
+          numSeqBytes += isSeqByte;
+          if (!isSeqByte)
+          {
+            if (numSeqBytes > 0)
+            {
+              U32 initialByte = ~(string.str[idx]) << 24;
+              U64 numLeadingBits = clz32(initialByte);
+              B32 isMultiByteSeq = numLeadingBits == numSeqBytes + 1;
+              if (isMultiByteSeq)
+              {
+                delta.x = -(numSeqBytes + 1);
+              }
+            }
+            break;
+          }
+        }
+      }
     }break;
     case UI_EventDeltaUnit_Word:
     {