Basic cursor movement, handling end of buffer, end of line in drawing

src/text_editor/buffer.cpp

@@ -252,17 +252,22 @@ Line FindLine(Buffer &buffer, int64_t pos) {
     return {};
 }
 
-int64_t AdjustUTF8Pos(const Buffer &buffer, int64_t pos, int64_t direction = 1) {
-    int64_t result = pos;
-    for (; result >= 0 && result < buffer.len;) {
-        char c = GetChar(buffer, pos);
-        if (IsUTF8ContinuationByte(c)) {
-            result += direction;
+int64_t AdjustUTF8Pos(String string, int64_t pos, int64_t direction) {
+    for (; pos >= 0 && pos < string.len;) {
+        if (IsUTF8ContinuationByte(string.data[pos])) {
+            pos += direction;
         } else {
             break;
         }
     }
-    return result;
+    return pos;
+}
+
+int64_t AdjustUTF8Pos(const Buffer &buffer, int64_t pos, int64_t direction = 1, bool clamp = true) {
+    String string = GetString(buffer);
+    pos           = AdjustUTF8Pos(string, pos, direction);
+    if (clamp) pos = Clamp(buffer, pos);
+    return pos;
 }
 
 uint32_t GetUTF32(Buffer &buffer, int64_t pos, int64_t *codepoint_size) {
@@ -317,7 +322,7 @@ void Advance(BufferIter *iter) {
     if (iter->direction == ITERATE_FORWARD) {
         iter->pos += iter->utf8_codepoint_size;
     } else {
-        iter->pos = AdjustUTF8Pos(*iter->buffer, iter->pos - 1, ITERATE_BACKWARD);
+        iter->pos = AdjustUTF8Pos(*iter->buffer, iter->pos - 1, ITERATE_BACKWARD, false);
     }
 
     if (!IsValid(*iter)) return;