fix RI at the top of the screen

3 files changed, 16 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index aecda1b..b428575 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@
 * Clearing cells now correctly sets the cell background color.
 * Fixed a couple bugs in wide character handling in `contents_formatted` and
   `contents_diff`.
+* Fixed RI when the cursor is at the top of the screen (fixes scrolling up in
+  `less`, for instance).
 
 ## [0.3.1] - 2019-11-06
 
diff --git a/src/grid.rs b/src/grid.rs
index ad2fa22..3c262fe 100644
--- a/src/grid.rs
+++ b/src/grid.rs
@@ -337,9 +337,16 @@ impl Grid {
     }
 
     pub fn row_dec_scroll(&mut self, count: u16) {
+        // need to account for clamping by both row_clamp_top and by
+        // saturating_sub
+        let extra_lines = if count > self.pos.row {
+            count - self.pos.row
+        } else {
+            0
+        };
         self.pos.row = self.pos.row.saturating_sub(count);
         let lines = self.row_clamp_top(true);
-        self.scroll_down(lines);
+        self.scroll_down(lines + extra_lines);
     }
 
     pub fn row_set(&mut self, i: u16) {
diff --git a/tests/escape.rs b/tests/escape.rs
index 0ad92ed..88c926a 100644
--- a/tests/escape.rs
+++ b/tests/escape.rs
@@ -15,6 +15,12 @@ fn ri() {
     let mut parser = vt100::Parser::new(24, 80);
     parser.process(b"foo\nbar\x1bMbaz");
     assert_eq!(parser.screen().contents(), "foo   baz\n   bar");
+
+    parser.process(b"\x1bc1\r\n2\r\n3\r\n4\r\n5\r\n6\r\n7\r\n8\r\n9\r\n10\r\n11\r\n12\r\n13\r\n14\r\n15\r\n16\r\n17\r\n18\r\n19\r\n20\r\n21\r\n22\r\n23\r\n24");
+    assert_eq!(parser.screen().contents(), "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n21\n22\n23\n24");
+
+    parser.process(b"\x1b[H\x1bM");
+    assert_eq!(parser.screen().contents(), "\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n21\n22\n23");
 }
 
 #[test]