Fix scrolling backwards in tmux

2 files changed, 14 insertions, 8 deletions

diff --git a/src/grid/mod.rs b/src/grid/mod.rs
index 1cb0876e..ca43471d 100644
--- a/src/grid/mod.rs
+++ b/src/grid/mod.rs
@@ -157,6 +157,10 @@ impl<T: Copy + Clone> Grid<T> {
         self.scroll_limit = min(self.scroll_limit + count, self.raw.len() - *self.lines);
     }
 
+    fn decrease_scroll_limit(&mut self, count: usize) {
+        self.scroll_limit = self.scroll_limit.saturating_sub(count);
+    }
+
     /// Add lines to the visible area
     ///
     /// The behavior in Terminal.app and iTerm.app is to keep the cursor at the
@@ -236,17 +240,16 @@ impl<T: Copy + Clone> Grid<T> {
             // active, the bottom lines are restored in the next step.
             self.raw.rotate_up(*positions);
 
+            self.decrease_scroll_limit(*positions);
+
             // Now, restore any scroll region lines
             let lines = self.lines;
             for i in IndexRange(region.end .. lines) {
-                // First do the swap
-                // TODO there is a bug here causing a panic.
-                // TODO math
                 self.raw.swap_lines(i, i + positions);
             }
 
             // Finally, reset recycled lines
-            for i in 0..*positions {
+            for i in IndexRange(Line(0)..positions) {
                 self.raw[i].reset(&self.template_row);
             }
         } else {
diff --git a/src/grid/storage.rs b/src/grid/storage.rs
index 0ca2f525..1588b006 100644
--- a/src/grid/storage.rs
+++ b/src/grid/storage.rs
@@ -62,6 +62,10 @@ impl<T> Storage<T> {
         (requested + self.zero) % self.len()
     }
 
+    fn compute_line_index(&self, requested: Line) -> usize {
+        ((self.len() + self.zero + *self.visible_lines) - *requested) % self.len()
+    }
+
     pub fn swap(&mut self, a: usize, b: usize) {
         let a = self.compute_index(a);
         let b = self.compute_index(b);
@@ -69,10 +73,9 @@ impl<T> Storage<T> {
     }
 
     pub fn swap_lines(&mut self, a: Line, b: Line) {
-        println!("visible: {}, a: {}, b: {}", self.visible_lines, a, b);
-        let a = self.visible_lines - a;
-        let b = self.visible_lines - b;
-        self.swap(*a, *b);
+        let a = self.compute_line_index(a);
+        let b = self.compute_line_index(b);
+        self.inner.swap(a, b);
     }
 
     pub fn iter_mut(&mut self) -> IterMut<T> {