From 9e5293a08e111c6965af7ab2551513511f42dc56 Mon Sep 17 00:00:00 2001
From: Fredrik Fornwall <fredrik@fornwall.net>
Date: Sat, 28 Oct 2017 10:54:47 +0200
Subject: [PATCH] Do not scroll when below bottom margin

---
 .../com/termux/terminal/TerminalEmulator.java  | 18 +++++++++++++-----
 .../com/termux/terminal/ScrollRegionTest.java  |  9 +++++++++
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/terminal-emulator/src/main/java/com/termux/terminal/TerminalEmulator.java b/terminal-emulator/src/main/java/com/termux/terminal/TerminalEmulator.java
index 10c7321d..9b947c34 100644
--- a/terminal-emulator/src/main/java/com/termux/terminal/TerminalEmulator.java
+++ b/terminal-emulator/src/main/java/com/termux/terminal/TerminalEmulator.java
@@ -1192,12 +1192,20 @@ public final class TerminalEmulator {
     }
 
     private void doLinefeed() {
+        boolean belowScrollingRegion = mCursorRow >= mBottomMargin;
         int newCursorRow = mCursorRow + 1;
-        if (newCursorRow >= mBottomMargin) {
-            scrollDownOneLine();
-            newCursorRow = mBottomMargin - 1;
+        if (belowScrollingRegion) {
+            // Move down (but not scroll) as long as we are above the last row.
+            if (mCursorRow != mRows - 1) {
+                setCursorRow(newCursorRow);
+            }
+        } else {
+            if (newCursorRow == mBottomMargin) {
+                scrollDownOneLine();
+                newCursorRow = mBottomMargin - 1;
+            }
+            setCursorRow(newCursorRow);
         }
-        setCursorRow(newCursorRow);
     }
 
     private void continueSequence(int state) {
@@ -1571,7 +1579,7 @@ public final class TerminalEmulator {
                 break;
             case 'r': // "CSI${top};${bottom}r" - set top and bottom Margins (DECSTBM).
             {
-                // http://www.vt100.net/docs/vt510-rm/DECSTBM
+                // https://vt100.net/docs/vt510-rm/DECSTBM.html
                 // The top margin defaults to 1, the bottom margin defaults to mRows.
                 // The escape sequence numbers top 1..23, but we number top 0..22.
                 // The escape sequence numbers bottom 2..24, and so do we (because we use a zero based numbering
diff --git a/terminal-emulator/src/test/java/com/termux/terminal/ScrollRegionTest.java b/terminal-emulator/src/test/java/com/termux/terminal/ScrollRegionTest.java
index b7e258a5..260a481a 100644
--- a/terminal-emulator/src/test/java/com/termux/terminal/ScrollRegionTest.java
+++ b/terminal-emulator/src/test/java/com/termux/terminal/ScrollRegionTest.java
@@ -98,4 +98,13 @@ public class ScrollRegionTest extends TerminalTestCase {
 		withTerminalSized(2, 5).enterString("1\r\n2\r\n3\r\n4\r\n5").assertLinesAre("1 ", "2 ", "3 ", "4 ", "5 ");
 		enterString("\033[3r").enterString("\033[2T").assertLinesAre("1 ", "2 ", "  ", "  ", "3 ");
 	}
+
+	public void testScrollDownBelowScrollRegion() {
+		withTerminalSized(2, 5).enterString("1\r\n2\r\n3\r\n4\r\n5").assertLinesAre("1 ", "2 ", "3 ", "4 ", "5 ");
+		enterString("\033[1;3r"); // DECSTBM margins.
+		enterString("\033[4;1H"); // Place cursor just below bottom margin.
+		enterString("QQ\r\nRR\r\n\r\n\r\nYY");
+		assertLinesAre("1 ", "2 ", "3 ", "QQ", "YY");
+	}
+
 }