buffer: Improve cursor movement

internal/buffer/cursor.go

@@ -601,24 +601,13 @@ func (c *Cursor) SubWordLeft() {
 
 // RuneUnder returns the rune under the given x position
 func (c *Cursor) RuneUnder(x int) rune {
-	line := c.buf.LineBytes(c.Y)
-	if len(line) == 0 || x >= util.CharacterCount(line) {
+	line := c.buf.LineCharacters(c.Y)
+	if len(line) == 0 || x >= len(line) {
 		return '\n'
 	} else if x < 0 {
 		x = 0
 	}
-	i := 0
-	for len(line) > 0 {
-		r, _, size := util.DecodeCharacter(line)
-		line = line[size:]
-
-		if i == x {
-			return r
-		}
-
-		i++
-	}
-	return '\n'
+	return line[x].combc[0]
 }
 
 func (c *Cursor) StoreVisualX() {

internal/buffer/line_array.go

@@ -371,18 +371,13 @@ func (la *LineArray) End() Loc {
 	return Loc{len(la.lines[numlines-1].runes), numlines - 1}
 }
 
-// Line returns line n as an array of runes
-func (la *LineArray) Line(n int) []rune {
+// LineCharacters returns line n as an array of characters
+func (la *LineArray) LineCharacters(n int) []Character {
 	if n >= len(la.lines) || n < 0 {
-		return []rune{}
+		return []Character{}
 	}
 
-	var runes []rune
-	for _, r := range la.lines[n].runes {
-		runes = append(runes, r.combc[0:]...)
-	}
-
-	return runes
+	return la.lines[n].runes
 }
 
 // LineBytes returns line n as an array of bytes