minor refactor

Author: ccbrown

packages/iocraft/src/canvas.rs

@@ -9,7 +9,7 @@ use std::{
 };
 use unicode_width::UnicodeWidthChar;
 
-#[derive(Clone)]
+#[derive(Clone, Debug, PartialEq)]
 struct Character {
     value: char,
     style: CanvasTextStyle,
@@ -28,7 +28,7 @@ pub struct CanvasTextStyle {
     pub underline: bool,
 }
 
-#[derive(Clone, Default)]
+#[derive(Clone, Default, PartialEq)]
 struct Cell {
     background_color: Option<Color>,
     character: Option<Character>,
@@ -43,6 +43,7 @@ impl Cell {
 /// Canvas is a low-level abstraction for rendering output. Most users of the library will not need
 /// to use it directly. However, it is used by low level component implementations and can be used
 /// to store and copy their output.
+#[derive(Clone, PartialEq)]
 pub struct Canvas {
     width: usize,
     cells: Vec<Vec<Cell>>,

packages/iocraft/src/render.rs

@@ -354,18 +354,19 @@ impl<'a> Tree<'a> {
         W: Write,
     {
         let mut terminal = Terminal::new()?;
-        let mut lines_to_rewind_to_clear = 0;
+        let mut prev_canvas: Option<Canvas> = None;
         loop {
             let width = terminal.width().ok().map(|w| w as usize);
             execute!(w, terminal::BeginSynchronizedUpdate,)?;
+            let lines_to_rewind_to_clear = prev_canvas.as_ref().map_or(0, |c| c.height());
             let output = self.render(width, Some(&mut terminal), lines_to_rewind_to_clear);
-            if !output.did_clear_terminal_output && lines_to_rewind_to_clear > 0 {
-                terminal.rewind_lines(lines_to_rewind_to_clear as _)?;
+            if output.did_clear_terminal_output || prev_canvas.as_ref() != Some(&output.canvas) {
+                if !output.did_clear_terminal_output {
+                    terminal.rewind_lines(lines_to_rewind_to_clear as _)?;
+                }
+                output.canvas.write_ansi(&mut w)?;
             }
-            // TODO: if we wanted to be efficient and the terminal wasn't cleared, we could
-            // only write the diff
-            output.canvas.write_ansi(&mut w)?;
-            lines_to_rewind_to_clear = output.canvas.height();
+            prev_canvas = Some(output.canvas);
             execute!(w, terminal::EndSynchronizedUpdate)?;
             if self.system_context.should_exit() || terminal.received_ctrl_c() {
                 break;

packages/iocraft/src/terminal.rs

@@ -181,7 +181,11 @@ impl Terminal {
     }
 
     pub fn rewind_lines(&mut self, lines: u16) -> io::Result<()> {
-        self.inner.rewind_lines(lines)
+        if lines > 0 {
+            self.inner.rewind_lines(lines)
+        } else {
+            Ok(())
+        }
     }
 
     pub fn received_ctrl_c(&self) -> bool {