Improve scrolling perforamnce (#54)

- Truncate text instead of using the native paragraph "scroll"

Author: dantleech

src/view/context.rs

@@ -57,7 +57,6 @@ impl View for ContextComponent {
             },
             None => return,
         };
-        let mut lines: Vec<Line> = vec![];
         let layout = Layout::default()
             .constraints([Constraint::Length(
                 if app.session_view.context_filter.show { 3 } else { 0 }
@@ -77,17 +76,22 @@ impl View for ContextComponent {
         }
 
         let mut filter_path = app.session_view.context_filter.segments().clone();
+
+        let mut lines: Vec<Line> = vec![];
+        let truncate_from = app.session_view.context_scroll.0 as u32;
         draw_properties(
             &app.theme(),
             &context.properties,
             &mut lines,
             0,
             &mut filter_path,
+            &truncate_from,
+            &mut 0
         );
 
 
         frame.render_widget(
-            Paragraph::new(lines).scroll(app.session_view.context_scroll),
+            Paragraph::new(lines.clone()),
             areas[1],
         );
     }

src/view/properties.rs

@@ -1,3 +1,4 @@
+
 use crate::dbgp::client::Property;
 use crate::dbgp::client::PropertyType;
 use crate::theme::Scheme;
@@ -10,6 +11,8 @@ pub fn draw_properties(
     lines: &mut Vec<Line>,
     level: usize,
     filter_path: &mut Vec<&str>,
+    truncate_until: &u32,
+    line_no: &mut u32,
 ) {
     let filter = filter_path.pop();
 
@@ -43,11 +46,18 @@ pub fn draw_properties(
             spans.push(Span::raw(delimiters.0).style(theme.syntax_brace));
         }
 
-        lines.push(Line::from(spans));
+        // only "render" lines that we need to
+        if *line_no >= *truncate_until {
+            lines.push(Line::from(spans));
+        }
+        *line_no += 1;
 
         if !property.children.is_empty() {
-            draw_properties(theme, &property.children, lines, level + 1, filter_path);
-            lines.push(Line::from(vec![Span::raw(delimiters.1)]).style(theme.syntax_brace));
+            draw_properties(theme, &property.children, lines, level + 1, filter_path, truncate_until,  line_no);
+            if *line_no >= *truncate_until {
+                lines.push(Line::from(vec![Span::raw(delimiters.1)]).style(theme.syntax_brace));
+            }
+            *line_no += 1;
         }
     }
 }
@@ -85,6 +95,8 @@ mod test {
             &mut lines,
             0,
             &mut Vec::new(),
+            &0,
+            &mut 0,
         );
         assert_eq!(0, lines.len());
         Ok(())
@@ -109,6 +121,8 @@ mod test {
             &mut lines,
             0,
             &mut Vec::new(),
+            &0,
+            &mut 0,
         );
         assert_eq!(vec![
             "foo string = \"\"{",
@@ -148,6 +162,8 @@ mod test {
             &mut lines,
             0,
             filter,
+            &0,
+            &mut 0,
         );
 
         assert_eq!(vec![

src/view/source.rs

@@ -51,8 +51,16 @@ impl View for SourceComponent {
             .analyzed_files
             .get(&stack.source.filename.to_string());
 
-        for (line_no, line) in stack.source.source.lines().enumerate() {
-            let is_current_line = stack.source.line_no == line_no as u32 + 1;
+
+        // trunacte the hidden lines
+        let truncate_until = app.session_view.source_scroll.0 as u32 + 1;
+
+        for (line_offset, line) in stack.source.source.lines().enumerate() {
+            let line_no = line_offset + 1;
+            if (line_no as u32) < truncate_until {
+                continue
+            }
+            let is_current_line = stack.source.line_no == line_no as u32;
 
             lines.push(Line::from(vec![
                 Span::styled(format!("{:<6}", line_no), app.theme().source_line_no),
@@ -68,7 +76,7 @@ impl View for SourceComponent {
 
             if is_current_line {
                 if let Some(analysis) = analysis {
-                    for (_, var) in analysis.row(line_no) {
+                    for (_, var) in analysis.row(line_offset) {
                         let property = stack.get_property(var.name.as_str());
                         if property.is_none() {
                             continue;
@@ -82,7 +90,7 @@ impl View for SourceComponent {
                     if labels.len() > 1 {
                         labels.pop();
                         annotations.push((
-                            line_no + 1,
+                            line_offset,
                             line.len() + 8,
                             Line::from(labels).style(app.theme().source_annotation),
                         ));
@@ -92,15 +100,15 @@ impl View for SourceComponent {
         }
 
         frame.render_widget(
-            Paragraph::new(lines.clone()).scroll(app.session_view.source_scroll),
+            Paragraph::new(lines.clone()),
             rows[0],
         );
 
-        for (line_no, line_length, line) in annotations {
+        for (line_offset, line_length, line) in annotations {
             let x_offset =  rows[0].x + (line_length as u16).saturating_sub(app.session_view.source_scroll.1);
             let area = Rect {
                 x: x_offset,
-                y: (line_no as u32).saturating_sub(app.session_view.source_scroll.0 as u32) as u16 + 1,
+                y: rows[0].y + ((line_offset as u32).saturating_sub(app.session_view.source_scroll.0 as u32) as u16),
                 width: rows[0].width.saturating_sub(x_offset),
                 height: 1,
             };