Support buffers with scrollback of 0, force alt as 0

Fixes #802

src/Buffer.test.ts

@@ -20,7 +20,7 @@ describe('Buffer', () => {
     terminal.cols = INIT_COLS;
     terminal.rows = INIT_ROWS;
     terminal.options.scrollback = 1000;
-    buffer = new Buffer(terminal);
+    buffer = new Buffer(terminal, false);
   });
 
   describe('constructor', () => {
@@ -145,4 +145,20 @@ describe('Buffer', () => {
       });
     });
   });
+
+  describe('alt buffer', () => {
+    it('should always have a scrollback of 0', () => {
+      assert.equal(terminal.options.scrollback, 1000);
+      // Test size on initialization
+      buffer = new Buffer(terminal, true);
+      buffer.fillViewportRows();
+      assert.equal(buffer.lines.maxLength, INIT_ROWS);
+      // Test size on buffer increase
+      buffer.resize(INIT_COLS, INIT_ROWS * 2);
+      assert.equal(buffer.lines.maxLength, INIT_ROWS * 2);
+      // Test size on buffer decrease
+      buffer.resize(INIT_COLS, INIT_ROWS / 2);
+      assert.equal(buffer.lines.maxLength, INIT_ROWS / 2);
+    });
+  });
 });

src/Buffer.ts

@@ -28,14 +28,12 @@ export class Buffer implements IBuffer {
 
   /**
    * Create a new Buffer.
-   * @param {Terminal} _terminal - The terminal the Buffer will belong to
-   * @param {number} ydisp - The scroll position of the Buffer in the viewport
-   * @param {number} ybase - The scroll position of the y cursor (ybase + y = the y position within the Buffer)
-   * @param {number} y - The cursor's y position after ybase
-   * @param {number} x - The cursor's x position after ybase
+   * @param _terminal The terminal the Buffer will belong to.
+   * @param _isAltBuffer Whether the buffer is the alt buffer.
    */
   constructor(
-    private _terminal: ITerminal
+    private _terminal: ITerminal,
+    private _isAltBuffer: boolean
   ) {
     this.clear();
   }
@@ -44,6 +42,20 @@ export class Buffer implements IBuffer {
     return this._lines;
   }
 
+  /**
+   * Gets the correct buffer length based on the rows provided, the terminal's
+   * scrollback and whether this is an alt buffer.
+   * @param rows The terminal rows to use in the calculation.
+   */
+  private _getCorrectBufferLength(rows: number): number {
+    // The alt buffer should never have scrollback.
+    // See http://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-The-Alternate-Screen-Buffer
+    if (this._isAltBuffer) {
+      return rows;
+    }
+    return rows + this._terminal.options.scrollback;
+  }
+
   /**
    * Fills the buffer's viewport with blank lines.
    */
@@ -67,7 +79,7 @@ export class Buffer implements IBuffer {
     this.scrollBottom = 0;
     this.scrollTop = 0;
     this.tabs = {};
-    this._lines = new CircularList<LineData>(this._terminal.rows + this._terminal.options.scrollback);
+    this._lines = new CircularList<LineData>(this._getCorrectBufferLength(this._terminal.rows));
     this.scrollBottom = this._terminal.rows - 1;
   }
 
@@ -82,6 +94,13 @@ export class Buffer implements IBuffer {
       return;
     }
 
+    // Increase max length if needed before adjustments to allow space to fill
+    // as required.
+    const newMaxLength = this._getCorrectBufferLength(newRows);
+    if (newMaxLength > this._lines.maxLength) {
+      this._lines.maxLength = newMaxLength;
+    }
+
     // Deal with columns increasing (we don't do anything when columns reduce)
     if (this._terminal.cols < newCols) {
       const ch: CharData = [this._terminal.defAttr, ' ', 1]; // does xterm use the default attr?
@@ -131,6 +150,19 @@ export class Buffer implements IBuffer {
       }
     }
 
+    // Reduce max length if needed after adjustments, this is done after as it
+    // would otherwise cut data from the bottom of the buffer.
+    if (newMaxLength < this._lines.maxLength) {
+      // Trim from the top of the buffer and adjust ybase and ydisp.
+      // const amountToTrim = this._lines.length - newMaxLength;
+      // if (amountToTrim > 0) {
+      //   this._lines.trimStart(amountToTrim);
+      //   this.ybase = Math.max(this.ybase - amountToTrim, 0);
+      //   this.ydisp = Math.max(this.ydisp - amountToTrim, 0);
+      // }
+      this._lines.maxLength = newMaxLength;
+    }
+
     // Make sure that the cursor stays on screen
     if (this.y >= newRows) {
       this.y = newRows - 1;

src/BufferSet.ts

@@ -21,9 +21,9 @@ export class BufferSet extends EventEmitter implements IBufferSet {
    */
   constructor(private _terminal: ITerminal) {
     super();
-    this._normal = new Buffer(this._terminal);
+    this._normal = new Buffer(this._terminal, false);
     this._normal.fillViewportRows();
-    this._alt = new Buffer(this._terminal);
+    this._alt = new Buffer(this._terminal, true);
     this._activeBuffer = this._normal;
   }
 
@@ -71,22 +71,10 @@ export class BufferSet extends EventEmitter implements IBufferSet {
     // Since the alt buffer is always cleared when the normal buffer is
     // activated, we want to fill it when switching to it.
     this._alt.fillViewportRows();
-
     this._activeBuffer = this._alt;
     this.emit('activate', this._alt);
   }
 
-  /**
-   * Refreshes the max length of the buffer set, this should be called whenever
-   * terminal rows or scrollback changes.
-   * @param rows The number of terminal rows.
-   */
-  public refreshMaxLength(rows: number): void {
-    this._normal.lines.maxLength = rows + this._terminal.options.scrollback;
-    // TODO: The alt buffer should never have scrollback, see https://github.com/sourcelair/xterm.js/issues/802
-    this._alt.lines.maxLength = rows + this._terminal.options.scrollback;
-  }
-
   /**
    * Resizes both normal and alt buffers, adjusting their data accordingly.
    * @param newCols The new number of columns.
@@ -95,6 +83,5 @@ export class BufferSet extends EventEmitter implements IBufferSet {
   public resize(newCols: number, newRows: number): void {
     this._normal.resize(newCols, newRows);
     this._alt.resize(newCols, newRows);
-    this.refreshMaxLength(newRows);
   }
 }

src/InputHandler.ts

@@ -442,23 +442,13 @@ export class InputHandler implements IInputHandler {
     }
     let row: number = this._terminal.buffer.y + this._terminal.buffer.ybase;
 
-    let j: number;
-    j = this._terminal.rows - 1 - this._terminal.buffer.scrollBottom;
-    j = this._terminal.rows - 1 + this._terminal.buffer.ybase - j + 1;
-
+    let scrollBottomRowsOffset = this._terminal.rows - 1 - this._terminal.buffer.scrollBottom;
+    let scrollBottomAbsolute = this._terminal.rows - 1 + this._terminal.buffer.ybase - scrollBottomRowsOffset + 1;
     while (param--) {
-      if (this._terminal.buffer.lines.length === this._terminal.buffer.lines.maxLength) {
-        // Trim the start of lines to make room for the new line
-        this._terminal.buffer.lines.trimStart(1);
-        this._terminal.buffer.ybase--;
-        this._terminal.buffer.ydisp--;
-        row--;
-        j--;
-      }
       // test: echo -e '\e[44m\e[1L\e[0m'
       // blankLine(true) - xterm/linux behavior
+      this._terminal.buffer.lines.splice(scrollBottomAbsolute - 1, 1);
       this._terminal.buffer.lines.splice(row, 0, this._terminal.blankLine(true));
-      this._terminal.buffer.lines.splice(j, 1);
     }
 
     // this.maxRange();
@@ -480,18 +470,11 @@ export class InputHandler implements IInputHandler {
     let j: number;
     j = this._terminal.rows - 1 - this._terminal.buffer.scrollBottom;
     j = this._terminal.rows - 1 + this._terminal.buffer.ybase - j;
-
     while (param--) {
-      if (this._terminal.buffer.lines.length === this._terminal.buffer.lines.maxLength) {
-        // Trim the start of lines to make room for the new line
-        this._terminal.buffer.lines.trimStart(1);
-        this._terminal.buffer.ybase -= 1;
-        this._terminal.buffer.ydisp -= 1;
-      }
       // test: echo -e '\e[44m\e[1M\e[0m'
       // blankLine(true) - xterm/linux behavior
-      this._terminal.buffer.lines.splice(j + 1, 0, this._terminal.blankLine(true));
-      this._terminal.buffer.lines.splice(row, 1);
+      this._terminal.buffer.lines.splice(row - 1, 1);
+      this._terminal.buffer.lines.splice(j, 0, this._terminal.blankLine(true));
     }
 
     // this.maxRange();

src/Terminal.ts

@@ -464,7 +464,7 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
         this.element.classList.toggle(`xterm-cursor-style-bar`, value === 'bar');
         break;
       case 'scrollback':
-        this.buffers.refreshMaxLength(this.rows);
+        this.buffers.resize(this.cols, this.rows);
         this.viewport.syncScrollArea();
         break;
       case 'tabStopWidth': this.setupStops(); break;
@@ -1177,17 +1177,16 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
     let row;
 
     // Make room for the new row in lines
-    if (this.buffer.lines.length === this.buffer.lines.maxLength) {
+    const bufferNeedsTrimming = this.buffer.lines.length === this.buffer.lines.maxLength;
+    if (bufferNeedsTrimming) {
       this.buffer.lines.trimStart(1);
       this.buffer.ybase--;
-      if (this.buffer.ydisp !== 0) {
-        this.buffer.ydisp--;
-      }
+      this.buffer.ydisp = Math.max(this.buffer.ydisp - 1, 0);
     }
 
     this.buffer.ybase++;
 
-    // TODO: Why is this done twice?
+    // Scroll the viewport down to the bottom if the user is not scrolling
     if (!this.userScrolling) {
       this.buffer.ydisp = this.buffer.ybase;
     }