Optimize rendering by using Ropey::byte_slice

This avoids costly conversions via byte_to_char (which are then
reversed back into bytes internally in Ropey).

Reduces time spent in slice/byte_to_char from ~24% to ~5%.

2 files changed, 3 insertions, 10 deletions

diff --git a/helix-core/src/graphemes.rs b/helix-core/src/graphemes.rs
index aa898684..c0c61775 100644
--- a/helix-core/src/graphemes.rs
+++ b/helix-core/src/graphemes.rs
@@ -333,10 +333,7 @@ impl<'a> Iterator for RopeGraphemes<'a> {
         }
 
         if a < self.cur_chunk_start {
-            let a_char = self.text.byte_to_char(a);
-            let b_char = self.text.byte_to_char(b);
-
-            Some(self.text.slice(a_char..b_char))
+            Some(self.text.byte_slice(a..b))
         } else {
             let a2 = a - self.cur_chunk_start;
             let b2 = b - self.cur_chunk_start;
diff --git a/helix-core/src/syntax.rs b/helix-core/src/syntax.rs
index 3fc91efc..f76683b9 100644
--- a/helix-core/src/syntax.rs
+++ b/helix-core/src/syntax.rs
@@ -576,9 +576,7 @@ pub struct Syntax {
 }
 
 fn byte_range_to_str(range: std::ops::Range<usize>, source: RopeSlice) -> Cow<str> {
-    let start_char = source.byte_to_char(range.start);
-    let end_char = source.byte_to_char(range.end);
-    Cow::from(source.slice(start_char..end_char))
+    Cow::from(source.byte_slice(range))
 }
 
 impl Syntax {
@@ -1197,9 +1195,7 @@ impl<'a> TextProvider<'a> for RopeProvider<'a> {
     type I = ChunksBytes<'a>;
 
     fn text(&mut self, node: Node) -> Self::I {
-        let start_char = self.0.byte_to_char(node.start_byte());
-        let end_char = self.0.byte_to_char(node.end_byte());
-        let fragment = self.0.slice(start_char..end_char);
+        let fragment = self.0.byte_slice(node.start_byte()..node.end_byte());
         ChunksBytes {
             chunks: fragment.chunks(),
         }