From 67f8919630be6be1e1af8a298d6c74e0a984314b Mon Sep 17 00:00:00 2001
From: Joscha <joscha@plugh.de>
Date: Sat, 21 May 2022 23:38:37 +0200
Subject: [PATCH] Only draw differences from previous frame

---
 src/buffer.rs   | 18 ++++++++----------
 src/terminal.rs |  5 ++++-
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/src/buffer.rs b/src/buffer.rs
index d8c169c..5b9092e 100644
--- a/src/buffer.rs
+++ b/src/buffer.rs
@@ -30,7 +30,7 @@ impl Pos {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Cell {
     pub content: Box<str>,
     pub style: ContentStyle,
@@ -67,6 +67,12 @@ impl Buffer {
         y * width + x
     }
 
+    pub(crate) fn at(&self, x: u16, y: u16) -> &Cell {
+        assert!(x < self.size.width);
+        assert!(y < self.size.height);
+        &self.data[self.index(x, y)]
+    }
+
     pub fn size(&self) -> Size {
         self.size
     }
@@ -143,14 +149,6 @@ pub struct Cells<'a> {
     y: u16,
 }
 
-impl<'a> Cells<'a> {
-    fn at(&self, x: u16, y: u16) -> &'a Cell {
-        assert!(x < self.buffer.size.width);
-        assert!(y < self.buffer.size.height);
-        &self.buffer.data[self.buffer.index(x, y)]
-    }
-}
-
 impl<'a> Iterator for Cells<'a> {
     type Item = (u16, u16, &'a Cell);
 
@@ -160,7 +158,7 @@ impl<'a> Iterator for Cells<'a> {
         }
 
         let (x, y) = (self.x, self.y);
-        let cell = self.at(self.x, self.y);
+        let cell = self.buffer.at(self.x, self.y);
         assert!(cell.offset == 0);
 
         self.x += cell.width as u16;
diff --git a/src/terminal.rs b/src/terminal.rs
index 2101e8b..b0055e6 100644
--- a/src/terminal.rs
+++ b/src/terminal.rs
@@ -98,8 +98,11 @@ impl Terminal {
     }
 
     fn draw_differences(&mut self) -> io::Result<()> {
-        // TODO Only draw the differences
         for (x, y, cell) in self.frame.buffer.cells() {
+            if self.prev_frame_buffer.at(x, y) == cell {
+                continue;
+            }
+
             let content = StyledContent::new(cell.style, &cell.content as &str);
             self.out
                 .queue(MoveTo(x, y))?