Clear alt buffer with erase attributes upon entering

src/Buffer.ts

@@ -114,11 +114,14 @@ export class Buffer implements IBuffer {
   /**
    * Fills the buffer's viewport with blank lines.
    */
-  public fillViewportRows(): void {
+  public fillViewportRows(fillAttr?: number): void {
     if (this.lines.length === 0) {
+      if (fillAttr === undefined) {
+        fillAttr = DEFAULT_ATTR;
+      }
       let i = this._terminal.rows;
       while (i--) {
-        this.lines.push(this.getBlankLine(DEFAULT_ATTR));
+        this.lines.push(this.getBlankLine(fillAttr));
       }
     }
   }

src/BufferSet.ts

@@ -77,13 +77,13 @@ export class BufferSet extends EventEmitter implements IBufferSet {
   /**
    * Sets the alt Buffer of the BufferSet as its currently active Buffer
    */
-  public activateAltBuffer(): void {
+  public activateAltBuffer(fillAttr?: number): void {
     if (this._activeBuffer === this._alt) {
       return;
     }
     // 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._alt.fillViewportRows(fillAttr);
     this._alt.x = this._normal.x;
     this._alt.y = this._normal.y;
     this._activeBuffer = this._alt;

src/InputHandler.test.ts

@@ -561,5 +561,10 @@ describe('InputHandler', () => {
       // Text color of 'TEST' should be red
       expect((term.buffer.lines.get(1).get(0)[CHAR_DATA_ATTR_INDEX] >> 9) & 0x1ff).to.equal(1);
     });
+    it('should handle DECSET/DECRST 1049 - clears alt buffer with erase attributes', () => {
+      handler.parse('\x1b[42m\x1b[?1049h');
+      // Buffer should be filled with green background
+      expect(term.buffer.lines.get(20).get(10)[CHAR_DATA_ATTR_INDEX] & 0x1ff).to.equal(2);
+    });
   });
 });

src/InputHandler.ts

@@ -1339,7 +1339,7 @@ export class InputHandler extends Disposable implements IInputHandler {
           // FALL-THROUGH
         case 47: // alt screen buffer
         case 1047: // alt screen buffer
-          this._terminal.buffers.activateAltBuffer();
+          this._terminal.buffers.activateAltBuffer(this._terminal.eraseAttr());
           this._terminal.refresh(0, this._terminal.rows - 1);
           if (this._terminal.viewport) {
             this._terminal.viewport.syncScrollArea();

src/Types.ts

@@ -306,7 +306,7 @@ export interface IBufferSet extends IEventEmitter {
   active: IBuffer;
 
   activateNormalBuffer(): void;
-  activateAltBuffer(): void;
+  activateAltBuffer(fillAttr?: number): void;
 }
 
 export interface ISelectionManager {