Add support for ESC[#X to VT100

This escape sequence can be generated when using Powershell on
Windows (and possibly other places too) to erase number of
characters.

Change-Id: I32405f51a3f91fd8653d44f2676a5c85b696ef99

Author: coehlrich

terminal/plugins/org.eclipse.tm.terminal.control/src/org/eclipse/tm/internal/terminal/emulator/IVT100EmulatorBackend.java

@@ -227,4 +227,11 @@ public interface IVT100EmulatorBackend {
 	 * scroll region.
 	 */
 	void processReverseLineFeed();
+
+	/**
+	 * Replaces characters from the cursor position with space characters.
+	 *
+	 * @param n  number of characters to replace
+	 */
+	void eraseCharacters(int n);
 }

terminal/plugins/org.eclipse.tm.terminal.control/src/org/eclipse/tm/internal/terminal/emulator/VT100BackendTraceDecorator.java

@@ -211,4 +211,9 @@ public void processReverseLineFeed() {
 		fBackend.processReverseLineFeed();
 	}
 
+	@Override
+	public void eraseCharacters(int n) {
+		fWriter.println("eraseCharacters(" + n + ")"); //$NON-NLS-1$ //$NON-NLS-2$
+		fBackend.eraseCharacters(n);
+	}
 }

terminal/plugins/org.eclipse.tm.terminal.control/src/org/eclipse/tm/internal/terminal/emulator/VT100Emulator.java

@@ -617,8 +617,7 @@ private void processAnsiCommandCharacter(char ansiCommandCharacter) {
 
 		case 'X':
 			// Erase character.
-			// Emacs, vi, and GNU readline don't seem to use this command, so we ignore
-			// it for now.
+			processAnsiCommand_X();
 			break;
 
 		case 'Z':
@@ -1238,6 +1237,13 @@ private void processAnsiCommand_T() {
 		text.scrollDown(getAnsiParameter(0));
 	}
 
+	/**
+	 * Erases n characters from cursor (default = 1 character)
+	 */
+	private void processAnsiCommand_X() {
+		text.eraseCharacters(getAnsiParameter(0));
+	}
+
 	private void processDecPrivateCommand_h() {
 		int param = getAnsiParameter(0);
 		switch (param) {

terminal/plugins/org.eclipse.tm.terminal.control/src/org/eclipse/tm/internal/terminal/emulator/VT100EmulatorBackend.java

@@ -490,4 +490,15 @@ public void scrollDown(int n) {
 			fTerminal.scroll(line, nLines, n);
 		}
 	}
+
+	@Override
+	public void eraseCharacters(int n) {
+		synchronized (fTerminal) {
+			int line = toAbsoluteLine(fCursorLine);
+			int end = Math.min(fCursorColumn + n, fColumns);
+			for (int col = fCursorColumn; col < end; col++) {
+				fTerminal.setChar(line, col, '\000', null);
+			}
+		}
+	}
 }