also add a rows_diff method

4 files changed, 109 insertions, 19 deletions

diff --git a/src/grid.rs b/src/grid.rs
index 075e604..fa6b4b9 100644
--- a/src/grid.rs
+++ b/src/grid.rs
@@ -177,7 +177,7 @@ impl Grid {
         for (idx, (row, prev_row)) in self.rows().zip(prev.rows()).enumerate()
         {
             let (mut new_contents, new_attrs, new_col) =
-                row.contents_diff(prev_row, prev_attrs);
+                row.contents_diff(prev_row, 0, self.size.cols, prev_attrs);
             if !new_contents.is_empty() {
                 contents.extend(format!("\x1b[{};1H", idx + 1).as_bytes());
                 final_row = idx.try_into().unwrap();
diff --git a/src/row.rs b/src/row.rs
index fb31594..7b2ab99 100644
--- a/src/row.rs
+++ b/src/row.rs
@@ -126,14 +126,21 @@ impl Row {
     pub fn contents_diff(
         &self,
         prev: &Self,
+        start: u16,
+        width: u16,
         attrs: crate::attrs::Attrs,
     ) -> (Vec<u8>, crate::attrs::Attrs, u16) {
         let mut skip = 0;
         let mut contents = vec![];
         let mut prev_attrs = attrs;
         let mut final_col = 0;
-        for (idx, (cell, prev_cell)) in
-            self.cells().zip(prev.cells()).enumerate()
+
+        for (idx, (cell, prev_cell)) in self
+            .cells()
+            .zip(prev.cells())
+            .skip(start as usize)
+            .take(width as usize)
+            .enumerate()
         {
             if cell == prev_cell {
                 skip += 1;
diff --git a/src/screen.rs b/src/screen.rs
index 6aa80ba..873eeb3 100644
--- a/src/screen.rs
+++ b/src/screen.rs
@@ -211,6 +211,33 @@ impl Screen {
         grid_contents
     }
 
+    /// Returns a sequence of terminal byte streams sufficient to turn the
+    /// subset of each row from `prev` (as described by `start` and `width`)
+    /// into the corresponding row subset in `self`.
+    ///
+    /// You must handle the initial row positioning yourself - each row diff
+    /// expects to start out positioned at the start of that row. Internal
+    /// terminal modes (such as application keypad mode or alternate screen
+    /// mode) will not be included here.
+    pub fn rows_diff<'a>(
+        &'a self,
+        prev: &'a Self,
+        start: u16,
+        width: u16,
+    ) -> impl Iterator<Item = Vec<u8>> + 'a {
+        self.grid().rows().zip(prev.grid().rows()).map(
+            move |(row, prev_row)| {
+                let (contents, ..) = row.contents_diff(
+                    prev_row,
+                    start,
+                    width,
+                    crate::attrs::Attrs::default(),
+                );
+                contents
+            },
+        )
+    }
+
     /// Returns the `Cell` object at the given location in the terminal, if it
     /// exists.
     pub fn cell(&self, row: u16, col: u16) -> Option<&crate::cell::Cell> {
diff --git a/tests/window_contents.rs b/tests/window_contents.rs
index 1d351cb..07a656d 100644
--- a/tests/window_contents.rs
+++ b/tests/window_contents.rs
@@ -72,8 +72,9 @@ fn empty_cells() {
 #[test]
 fn rows() {
     let mut parser = vt100::Parser::new(24, 80);
+    let screen1 = parser.screen().clone();
     assert_eq!(
-        parser.screen().rows(0, 80).collect::<Vec<String>>(),
+        screen1.rows(0, 80).collect::<Vec<String>>(),
         vec![
             String::new(),
             String::new(),
@@ -102,10 +103,7 @@ fn rows() {
         ]
     );
     assert_eq!(
-        parser
-            .screen()
-            .rows_formatted(0, 80)
-            .collect::<Vec<Vec<u8>>>(),
+        screen1.rows_formatted(0, 80).collect::<Vec<Vec<u8>>>(),
         vec![
             vec![],
             vec![],
@@ -134,7 +132,7 @@ fn rows() {
         ]
     );
     assert_eq!(
-        parser.screen().rows(5, 15).collect::<Vec<String>>(),
+        screen1.rows(5, 15).collect::<Vec<String>>(),
         vec![
             String::new(),
             String::new(),
@@ -163,10 +161,7 @@ fn rows() {
         ]
     );
     assert_eq!(
-        parser
-            .screen()
-            .rows_formatted(5, 15)
-            .collect::<Vec<Vec<u8>>>(),
+        screen1.rows_formatted(5, 15).collect::<Vec<Vec<u8>>>(),
         vec![
             vec![],
             vec![],
@@ -197,8 +192,9 @@ fn rows() {
 
     parser
         .process(b"\x1b[31mfoo\x1b[10;10H\x1b[32mbar\x1b[20;20H\x1b[33mbaz");
+    let screen2 = parser.screen().clone();
     assert_eq!(
-        parser.screen().rows(0, 80).collect::<Vec<String>>(),
+        screen2.rows(0, 80).collect::<Vec<String>>(),
         vec![
             "foo".to_string(),
             String::new(),
@@ -227,8 +223,7 @@ fn rows() {
         ]
     );
     assert_eq!(
-        parser
-            .screen()
+        screen2
             .rows_formatted(0, 80)
             .collect::<Vec<Vec<u8>>>(),
         vec![
@@ -259,7 +254,7 @@ fn rows() {
         ]
     );
     assert_eq!(
-        parser.screen().rows(5, 15).collect::<Vec<String>>(),
+        screen2.rows(5, 15).collect::<Vec<String>>(),
         vec![
             String::new(),
             String::new(),
@@ -288,8 +283,7 @@ fn rows() {
         ]
     );
     assert_eq!(
-        parser
-            .screen()
+        screen2
             .rows_formatted(5, 15)
             .collect::<Vec<Vec<u8>>>(),
         vec![
@@ -319,6 +313,68 @@ fn rows() {
             vec![],
         ]
     );
+
+    assert_eq!(
+        screen2.rows_diff(&screen1, 0, 80).collect::<Vec<Vec<u8>>>(),
+        vec![
+            b"\x1b[31mfoo".to_vec(),
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            b"\x1b[9C\x1b[32mbar".to_vec(),
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            b"\x1b[19C\x1b[33mbaz".to_vec(),
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+        ]
+    );
+
+    parser.process(b"\x1b[10;11Ho");
+    let screen3 = parser.screen().clone();
+    assert_eq!(
+        screen3.rows_diff(&screen2, 0, 80).collect::<Vec<Vec<u8>>>(),
+        vec![
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            b"\x1b[10C\x1b[33mo".to_vec(),
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+            vec![],
+        ]
+    );
 }
 
 #[test]