perf(previews): avoid unnecessary preview content copy (#507)

television/channels/entry.rs

@@ -2,12 +2,6 @@ use std::hash::{Hash, Hasher};
 
 use devicons::FileIcon;
 
-// NOTE: having an enum for entry types would be nice since it would allow
-// having a nicer implementation for transitions between channels. This would
-// permit implementing `From<EntryType>` for channels which would make the
-// channel convertible from any other that yields `EntryType`.
-// This needs pondering since it does bring another level of abstraction and
-// adds a layer of complexity.
 #[derive(Clone, Debug, Eq)]
 pub struct Entry {
     /// The name of the entry.

television/previewer/state.rs

@@ -9,6 +9,8 @@ pub struct PreviewState {
 }
 
 const PREVIEW_MIN_SCROLL_LINES: u16 = 3;
+pub const ANSI_BEFORE_CONTEXT_SIZE: u16 = 10;
+const ANSI_CONTEXT_SIZE: usize = 500;
 
 impl PreviewState {
     pub fn new(
@@ -55,4 +57,28 @@ impl PreviewState {
             self.target_line = target_line;
         }
     }
+
+    pub fn for_render_context(&self) -> Self {
+        let skipped_lines =
+            self.scroll.saturating_sub(ANSI_BEFORE_CONTEXT_SIZE);
+        let cropped_content = self
+            .preview
+            .content
+            .lines()
+            .skip(skipped_lines as usize)
+            .take(ANSI_CONTEXT_SIZE)
+            .collect::<Vec<_>>()
+            .join("\n");
+        PreviewState::new(
+            self.enabled,
+            Preview::new(
+                &self.preview.title,
+                cropped_content,
+                self.preview.icon,
+                self.preview.total_lines,
+            ),
+            skipped_lines,
+            self.target_line,
+        )
+    }
 }

television/screen/preview.rs

@@ -32,21 +32,13 @@ pub fn draw_preview_content_block(
         use_nerd_font_icons,
     )?;
     // render the preview content
-    let rp = build_preview_paragraph(
-        &preview_state.preview.content,
-        preview_state.target_line,
-        preview_state.scroll,
-    );
+    let rp = build_preview_paragraph(&preview_state.preview.content);
     f.render_widget(rp, inner);
 
     Ok(())
 }
 
-pub fn build_preview_paragraph(
-    preview_content: &str,
-    #[allow(unused_variables)] target_line: Option<u16>,
-    preview_scroll: u16,
-) -> Paragraph<'_> {
+pub fn build_preview_paragraph(content: &str) -> Paragraph<'_> {
     let preview_block =
         Block::default().style(Style::default()).padding(Padding {
             top: 0,
@@ -55,42 +47,14 @@ pub fn build_preview_paragraph(
             left: 1,
         });
 
-    build_ansi_text_paragraph(preview_content, preview_block, preview_scroll)
+    build_ansi_text_paragraph(content, preview_block)
 }
 
-const ANSI_BEFORE_CONTEXT_SIZE: u16 = 10;
-const ANSI_CONTEXT_SIZE: usize = 150;
-
 fn build_ansi_text_paragraph<'a>(
     text: &'a str,
     preview_block: Block<'a>,
-    preview_scroll: u16,
 ) -> Paragraph<'a> {
-    let lines = text.lines();
-    let skip =
-        preview_scroll.saturating_sub(ANSI_BEFORE_CONTEXT_SIZE) as usize;
-    let context = lines
-        .skip(skip)
-        .take(ANSI_CONTEXT_SIZE)
-        .collect::<Vec<_>>()
-        .join("\n");
-
-    let mut text = "\n".repeat(skip);
-    text.push_str(
-        &replace_non_printable(
-            context.as_bytes(),
-            &ReplaceNonPrintableConfig {
-                replace_line_feed: false,
-                replace_control_characters: false,
-                ..Default::default()
-            },
-        )
-        .0,
-    );
-
-    Paragraph::new(text.into_text().unwrap())
-        .block(preview_block)
-        .scroll((preview_scroll, 0))
+    Paragraph::new(text.into_text().unwrap()).block(preview_block)
 }
 
 pub fn build_meta_preview_paragraph<'a>(

television/television.rs

@@ -187,9 +187,7 @@ impl Television {
             self.rc_picker.clone(),
             channel_state,
             self.spinner,
-            // PERF: we shouldn't need to clone the whole preview here but only
-            // what's in range of the preview window
-            self.preview_state.clone(),
+            self.preview_state.for_render_context(),
         );
 
         Ctx::new(
@@ -197,7 +195,6 @@ impl Television {
             self.config.clone(),
             self.colorscheme.clone(),
             self.app_metadata.clone(),
-            // now timestamp
             std::time::Instant::now(),
             self.ui_state.layout,
         )