Added: Add `SCROLL` extra key to toggle auto scrolling of terminal to bottom on terminal text updates and termux activity return

The toggle will apply to each terminal session separately.

Closes #2535

app/src/main/java/com/termux/app/terminal/io/TermuxTerminalExtraKeys.java

@@ -96,6 +96,10 @@ public class TermuxTerminalExtraKeys extends TerminalExtraKeys {
         } else if ("PASTE".equals(key)) {
             if(mTermuxTerminalSessionActivityClient != null)
                 mTermuxTerminalSessionActivityClient.onPasteTextFromClipboard(null);
+        }  else if ("SCROLL".equals(key)) {
+            TerminalView terminalView = mTermuxTerminalViewClient.getActivity().getTerminalView();
+            if (terminalView != null && terminalView.mEmulator != null)
+                terminalView.mEmulator.toggleAutoScrollDisabled();
         } else {
             super.onTerminalExtraKeyButtonClick(view, key, ctrlDown, altDown, shiftDown, fnDown);
         }

terminal-emulator/src/main/java/com/termux/terminal/TerminalEmulator.java

@@ -252,6 +252,9 @@ public final class TerminalEmulator {
      */
     private int mScrollCounter = 0;
 
+    /** If automatic scrolling of terminal is disabled */
+    private boolean mAutoScrollDisabled;
+
     private byte mUtf8ToFollow, mUtf8Index;
     private final byte[] mUtf8InputBuffer = new byte[4];
     private int mLastEmittedCodePoint = -1;
@@ -2412,6 +2415,15 @@ public final class TerminalEmulator {
         mScrollCounter = 0;
     }
 
+    public boolean isAutoScrollDisabled() {
+        return mAutoScrollDisabled;
+    }
+
+    public void toggleAutoScrollDisabled() {
+        mAutoScrollDisabled = !mAutoScrollDisabled;
+    }
+
+
     /** Reset terminal state so user can interact with it regardless of present state. */
     public void reset() {
         setCursorStyle();

terminal-view/src/main/java/com/termux/view/TerminalView.java

@@ -409,19 +409,29 @@ public final class TerminalView extends View {
     }
 
     public void onScreenUpdated() {
+        onScreenUpdated(false);
+    }
+
+    public void onScreenUpdated(boolean skipScrolling) {
         if (mEmulator == null) return;
 
         int rowsInHistory = mEmulator.getScreen().getActiveTranscriptRows();
         if (mTopRow < -rowsInHistory) mTopRow = -rowsInHistory;
 
-        boolean skipScrolling = false;
+        if (isSelectingText() || mEmulator.isAutoScrollDisabled()) {
-        if (isSelectingText()) {
+
             // Do not scroll when selecting text.
             int rowShift = mEmulator.getScrollCounter();
             if (-mTopRow + rowShift > rowsInHistory) {
                 // .. unless we're hitting the end of history transcript, in which
                 // case we abort text selection and scroll to end.
-                stopTextSelectionMode();
+                if (isSelectingText())
+                    stopTextSelectionMode();
+
+                if (mEmulator.isAutoScrollDisabled()) {
+                    mTopRow = -rowsInHistory;
+                    skipScrolling = true;
+                }
             } else {
                 skipScrolling = true;
                 mTopRow -= rowShift;

termux-shared/src/main/java/com/termux/shared/termux/extrakeys/ExtraKeysConstants.java

@@ -90,6 +90,7 @@ public class ExtraKeysConstants {
             put("DRAWER", "☰"); // U+2630 ☰ TRIGRAM FOR HEAVEN not well known but easy to understand
             put("KEYBOARD", "⌨"); // U+2328 ⌨ KEYBOARD not well known but easy to understand
             put("PASTE", "⎘"); // U+2398
+            put("SCROLL", "⇳"); // U+21F3
         }};
 
         public static final ExtraKeyDisplayMap LESS_KNOWN_CHARACTERS_DISPLAY = new ExtraKeyDisplayMap() {{