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%.

1 files changed, 3 insertions, 4 deletions

diff --git a/helix-term/src/ui/editor.rs b/helix-term/src/ui/editor.rs
index 31a9bfc8..2b9de5d6 100644
--- a/helix-term/src/ui/editor.rs
+++ b/helix-term/src/ui/editor.rs
@@ -183,6 +183,7 @@ impl EditorView {
                     .highlight_iter(text.slice(..), Some(range), None)
                     .map(|event| event.unwrap())
                     .map(move |event| match event {
+                        // TODO: use byte slices directly
                         // convert byte offsets to char offset
                         HighlightEvent::Source { start, end } => {
                             let start =
@@ -317,6 +318,8 @@ impl EditorView {
         theme: &Theme,
         highlights: H,
     ) {
+        // It's slightly more efficient to produce a full RopeSlice from the Rope, then slice that a bunch
+        // of times than it is to always call Rope::slice/get_slice (it will internally always hit RSEnum::Light).
         let text = doc.text().slice(..);
 
         let mut spans = Vec::new();
@@ -327,10 +330,6 @@ impl EditorView {
 
         let text_style = theme.get("ui.text");
 
-        // It's slightly more efficient to produce a full RopeSlice from the Rope, then slice that a bunch
-        // of times than it is to always call Rope::slice/get_slice (it will internally always hit RSEnum::Light).
-        let text = text.slice(..);
-
         'outer: for event in highlights {
             match event {
                 HighlightEvent::HighlightStart(span) => {