How had I not tested on Linux before

lib3270j/src/main/java/org/lib3270j/input/InputProcessor.java

@@ -152,6 +152,7 @@ public class InputProcessor {
         }
         screen.setCursorAddress(baddr);
         screen.markAllChanged();
+        screen.updateDisplaySnapshot();
     }
 
     /**
@@ -206,6 +207,7 @@ public class InputProcessor {
             int nextRowAddr = ((row + 1) % screen.getRows()) * cols;
             screen.setCursorAddress(nextRowAddr);
             screen.markAllChanged();
+            screen.updateDisplaySnapshot();
             setKeyboardLocked(false);
             return;
         }
@@ -309,6 +311,7 @@ public class InputProcessor {
         addr -= screen.getCols();
         if (addr < 0) addr += screen.getRows() * screen.getCols();
         screen.setCursorAddress(addr);
+        screen.updateDisplaySnapshot();
     }
 
     public void cursorDown() {
@@ -316,18 +319,21 @@ public class InputProcessor {
         addr += screen.getCols();
         if (addr >= screen.getRows() * screen.getCols()) addr -= screen.getRows() * screen.getCols();
         screen.setCursorAddress(addr);
+        screen.updateDisplaySnapshot();
     }
 
     public void cursorLeft() {
         int addr = screen.getCursorAddress();
         addr = screen.decrementAddress(addr);
         screen.setCursorAddress(addr);
+        screen.updateDisplaySnapshot();
     }
 
     public void cursorRight() {
         int addr = screen.getCursorAddress();
         addr = screen.incrementAddress(addr);
         screen.setCursorAddress(addr);
+        screen.updateDisplaySnapshot();
     }
 
     public void cursorHome() {
@@ -336,11 +342,13 @@ public class InputProcessor {
         } else {
             screen.setCursorAddress(0);
         }
+        screen.updateDisplaySnapshot();
     }
 
     public void tab() {
         int addr = screen.findNextUnprotected(screen.getCursorAddress());
         screen.setCursorAddress(addr);
+        screen.updateDisplaySnapshot();
     }
 
     public int getLastAid() { return lastAid; }
@@ -348,6 +356,7 @@ public class InputProcessor {
 
     public void setCursorAddress(int baddr) {
         screen.setCursorAddress(baddr);
+        screen.updateDisplaySnapshot();
     }
 
     public void backTab() {
@@ -361,6 +370,7 @@ public class InputProcessor {
             if (screen.getCell(addr).isFieldAttribute()) {
                 if (!faIsProtected(screen.getCell(addr).fa & 0xFF)) {
                     screen.setCursorAddress(screen.incrementAddress(addr));
+                    screen.updateDisplaySnapshot();
                     return;
                 }
             }
@@ -377,6 +387,7 @@ public class InputProcessor {
                 ea.ucs4 = 0;
             }
             screen.markAllChanged();
+            screen.updateDisplaySnapshot();
             return;
         }
         int addr = screen.getCursorAddress();
@@ -398,6 +409,7 @@ public class InputProcessor {
             screen.getCell(faAddr).fa = (byte) (screen.getCell(faAddr).fa | FA_MODIFY);
         }
         screen.markAllChanged();
+        screen.updateDisplaySnapshot();
     }
 
     public void deleteChar() {
@@ -426,6 +438,7 @@ public class InputProcessor {
             screen.getCell(faAddr).fa = (byte) (screen.getCell(faAddr).fa | FA_MODIFY);
         }
         screen.markAllChanged();
+        screen.updateDisplaySnapshot();
     }
 
     public void backspace() {
@@ -439,6 +452,7 @@ public class InputProcessor {
         if (keyboardLocked) return;
         screen.eraseAllUnprotected();
         screen.markAllChanged();
+        screen.updateDisplaySnapshot();
     }
 
     /** Move cursor to first unprotected field on next line (Newline key in 3270). */
@@ -455,6 +469,7 @@ public class InputProcessor {
         }
         screen.setCursorAddress(target);
         screen.markAllChanged();
+        screen.updateDisplaySnapshot();
     }
 
     /** Insert Duplicate (DUP) code and advance to next field. */
@@ -472,6 +487,8 @@ public class InputProcessor {
             screen.getCell(faAddr).fa = (byte) (screen.getCell(faAddr).fa | FA_MODIFY);
         }
         tab();
+        screen.markAllChanged();
+        screen.updateDisplaySnapshot();
     }
 
     /** Insert Field Mark (FM) code. */
@@ -495,6 +512,7 @@ public class InputProcessor {
         }
         screen.setCursorAddress(baddr);
         screen.markAllChanged();
+        screen.updateDisplaySnapshot();
     }
 
     /** Attention key (sends Telnet IP). */
@@ -571,6 +589,7 @@ public class InputProcessor {
                 screen.getCell(i).ucs4 = 0;
             }
             screen.markAllChanged();
+            screen.updateDisplaySnapshot();
             return size;
         }
 
@@ -608,6 +627,7 @@ public class InputProcessor {
             screen.getCell(faAddr).fa = (byte) (screen.getCell(faAddr).fa | FA_MODIFY);
         }
         screen.markAllChanged();
+        screen.updateDisplaySnapshot();
         return fieldLen;
     }
 

lib3270j/src/main/java/org/lib3270j/screen/ScreenBuffer.java

@@ -60,6 +60,7 @@ public class ScreenBuffer {
         defaultFA.ic = 1;
 
         allocateBuffers();
+        updateDisplaySnapshot();
     }
 
     private void allocateBuffers() {
@@ -139,7 +140,7 @@ public class ScreenBuffer {
     public boolean isScreenAlt() { return screenAlt; }
 
     /** Update alternate dimensions from BIND image. Re-allocates buffers if needed. */
-    public void setAlternateDimensions(int newAltRows, int newAltCols) {
+    public synchronized void setAlternateDimensions(int newAltRows, int newAltCols) {
         if (newAltRows == altRows && newAltCols == altCols) return;
         this.altRows = newAltRows;
         this.altCols = newAltCols;
@@ -149,11 +150,15 @@ public class ScreenBuffer {
             this.maxCols = Math.max(maxCols, newAltCols);
             allocateBuffers();
         }
+        updateDisplaySnapshot();
     }
 
     // ========== Cursor ==========
     public int getCursorAddress()                  { return cursorAddress; }
-    public void setCursorAddress(int addr)         { this.cursorAddress = addr; }
+    public synchronized void setCursorAddress(int addr) {
+        this.cursorAddress = addr;
+        this.displayCursorAddress = addr;
+    }
     public int getCursorRow()                      { return cursorAddress / cols; }
     public int getCursorCol()                      { return cursorAddress % cols; }
 
@@ -168,20 +173,22 @@ public class ScreenBuffer {
     /**
      * Perform an erase, optionally using the alternate screen size.
      */
-    public void erase(boolean alt) {
+    public synchronized void erase(boolean alt) {
         clear();
         int newRows = alt ? altRows : defRows;
         int newCols = alt ? altCols : defCols;
         if (alt == screenAlt && rows == newRows && cols == newCols) {
+            updateDisplaySnapshot();
             return;
         }
         rows = newRows;
         cols = newCols;
         screenAlt = alt;
+        updateDisplaySnapshot();
     }
 
     /** Clear the entire buffer. */
-    public void clear() {
+    public synchronized void clear() {
         for (ExtendedAttribute ea : buffer) {
             ea.clear();
         }
@@ -196,12 +203,13 @@ public class ScreenBuffer {
         defaultCs = 0x00;
         defaultIc = 0x00;
         replyMode = SF_SRM_FIELD;
+        updateDisplaySnapshot();
     }
 
     /**
      * Erase all unprotected fields.
      */
-    public void eraseAllUnprotected() {
+    public synchronized void eraseAllUnprotected() {
         int size = rows * cols;
         boolean inUnprotected = false;
 
@@ -229,6 +237,7 @@ public class ScreenBuffer {
         // Move cursor to first unprotected field
         cursorAddress = findNextUnprotected(0);
         screenChanged = true;
+        updateDisplaySnapshot();
     }
 
     // ========== Field attribute navigation ==========
@@ -322,7 +331,7 @@ public class ScreenBuffer {
 
     // ========== Setters for model reconfiguration ==========
 
-    public void setDimensions(int maxRows, int maxCols, int defRows, int defCols,
+    public synchronized void setDimensions(int maxRows, int maxCols, int defRows, int defCols,
                                int altRows, int altCols) {
         this.maxRows = maxRows;
         this.maxCols = maxCols;
@@ -333,6 +342,7 @@ public class ScreenBuffer {
         this.rows = defRows;
         this.cols = defCols;
         allocateBuffers();
+        updateDisplaySnapshot();
     }
 
     public void translateToUnicode() {

lib3270j/src/test/java/org/lib3270j/input/InputProcessorTest.java

@@ -44,10 +44,91 @@ public class InputProcessorTest {
 
         assertEquals('A', screen.getCell(1).ucs4);
         assertEquals('B', screen.getCell(2).ucs4);
+        assertEquals('A', screen.getDisplayCell(1).ucs4);
+        assertEquals('B', screen.getDisplayCell(2).ucs4);
 
         input.eraseInput();
 
         assertEquals(0, screen.getCell(1).ec);
         assertEquals(0, screen.getCell(2).ec);
+        assertEquals(0, screen.getDisplayCell(1).ec);
+        assertEquals(0, screen.getDisplayCell(2).ec);
+    }
+
+    @Test
+    public void testTypeCharacterUpdatesDisplaySnapshot() {
+        InputProcessor input = new InputProcessor(screen, translator, null);
+        screen.erase(false);
+        screen.setCellFA(0, (byte) FA_PRINTABLE); // Unprotected field starting at 1
+        screen.setCursorAddress(1);
+        screen.updateDisplaySnapshot(); // Initial snapshot
+
+        // Type "logon"
+        input.typeCharacter('l');
+        input.typeCharacter('o');
+        input.typeCharacter('g');
+        input.typeCharacter('o');
+        input.typeCharacter('n');
+
+        // Verify underlying buffer
+        assertEquals('l', screen.getCell(1).ucs4);
+        assertEquals('o', screen.getCell(2).ucs4);
+        assertEquals('g', screen.getCell(3).ucs4);
+        assertEquals('o', screen.getCell(4).ucs4);
+        assertEquals('n', screen.getCell(5).ucs4);
+
+        // Verify display snapshot (what TerminalPanel renders)
+        assertEquals('l', screen.getDisplayCell(1).ucs4);
+        assertEquals('o', screen.getDisplayCell(2).ucs4);
+        assertEquals('g', screen.getDisplayCell(3).ucs4);
+        assertEquals('o', screen.getDisplayCell(4).ucs4);
+        assertEquals('n', screen.getDisplayCell(5).ucs4);
+        assertEquals(6, screen.getDisplayCursorAddress());
+        assertEquals(6, screen.getCursorAddress());
+    }
+
+    @Test
+    public void testCursorMovementUpdatesDisplayCursorAddress() {
+        InputProcessor input = new InputProcessor(screen, translator, null);
+        screen.erase(false);
+        screen.setCursorAddress(10);
+        assertEquals(10, screen.getDisplayCursorAddress());
+
+        input.cursorRight();
+        assertEquals(11, screen.getDisplayCursorAddress());
+
+        input.cursorLeft();
+        assertEquals(10, screen.getDisplayCursorAddress());
+
+        screen.setCursorAddress(45);
+        assertEquals(45, screen.getDisplayCursorAddress());
+    }
+
+    @Test
+    public void testDeleteAndEraseEofUpdateDisplaySnapshot() {
+        InputProcessor input = new InputProcessor(screen, translator, null);
+        screen.erase(false);
+        screen.setCellFA(0, (byte) FA_PRINTABLE);
+        screen.setCellFA(10, (byte) (FA_PRINTABLE | FA_PROTECT));
+        screen.setCursorAddress(1);
+
+        input.typeCharacter('A');
+        input.typeCharacter('B');
+        input.typeCharacter('C');
+        assertEquals('A', screen.getDisplayCell(1).ucs4);
+        assertEquals('B', screen.getDisplayCell(2).ucs4);
+        assertEquals('C', screen.getDisplayCell(3).ucs4);
+
+        // Backspace over 'C'
+        input.backspace();
+        assertEquals(3, screen.getCursorAddress());
+        assertEquals(3, screen.getDisplayCursorAddress());
+        assertEquals(0, screen.getDisplayCell(3).ucs4);
+
+        // Erase EOF from position 2 ('B')
+        screen.setCursorAddress(2);
+        input.eraseEof();
+        assertEquals(0, screen.getDisplayCell(2).ucs4);
+        assertEquals('A', screen.getDisplayCell(1).ucs4);
     }
 }