fixed unicode chars printed wrong in WriteString

write_string.go

@@ -3,11 +3,13 @@ package buf2d
 // WriteString writes a whole string to the buffer at position (x,y)
 // no word wrap is applied at all. If the string does not fit, it will be truncated
 func (b *Buffer) WriteString(str string, x, y int) {
-	for dx, r := range str {
-		if x+dx >= b.width {
+	dx := x
+	for _, r := range str {
+		if dx >= b.width {
 			return
 		}
-		b.Set(x+dx, y, r)
+		b.Set(dx, y, r)
+		dx++
 	}
 }