fix: preserve scroll position when terminal shrinks

lib/Emulation.cpp

@@ -320,6 +320,7 @@ void Emulation::showBulk()
 
     _currentScreen->resetScrolledLines();
     _currentScreen->resetDroppedLines();
+    _currentScreen->resetResizePushedLines();
 }
 
 void Emulation::bufferedUpdate()

lib/Screen.cpp

@@ -70,6 +70,7 @@ Character Screen::defaultChar = Character(' ',
     screenLines(new ImageLine[lines+1] ),
     _scrolledLines(0),
     _droppedLines(0),
+    _resizePushedLines(0),
     history(new HistoryScrollNone()),
     cuX(0), cuY(0),
     currentRendition(0),
@@ -349,6 +350,7 @@ void Screen::resizeImage(int new_lines, int new_columns)
         for (int i = 0; i < cuY-(new_lines-1); i++)
         {
             addHistLine(); scrollUp(0,1);
+            ++_resizePushedLines;
         }
     }
 
@@ -884,6 +886,14 @@ void Screen::resetScrolledLines()
 {
     _scrolledLines = 0;
 }
+int Screen::resizePushedLines() const
+{
+    return _resizePushedLines;
+}
+void Screen::resetResizePushedLines()
+{
+    _resizePushedLines = 0;
+}
 
 void Screen::scrollUp(int n)
 {

lib/Screen.h

@@ -555,6 +555,9 @@ class Screen
      */
     void resetDroppedLines();
 
+    int resizePushedLines() const;
+    void resetResizePushedLines();
+
     /**
       * Fills the buffer @p dest with @p count instances of the default (ie. blank)
       * Character style.
@@ -647,6 +650,7 @@ class Screen
     QRect _lastScrolledRegion;
 
     int _droppedLines;
+    int _resizePushedLines;
 
     QVarLengthArray<LineProperty,64> lineProperties;
 

lib/ScreenWindow.cpp

@@ -282,6 +282,12 @@ void ScreenWindow::notifyOutputChanged()
         _currentLine = qMax(0,_currentLine -
                               _screen->droppedLines());
 
+        // When the terminal shrinks, resizeImage() pushes excess screen
+        // lines into history to keep the cursor in view.  Advance
+        // _currentLine by the same amount so the viewport stays
+        // bottom-anchored instead of jumping towards the top.
+        _currentLine += _screen->resizePushedLines();
+
         // ensure that the screen window's current position does
         // not go beyond the bottom of the screen
         _currentLine = qMin( _currentLine , _screen->getHistLines() );