Support callback on scrollLines

[unional]

I tried to implement cursor based navigation.

When trying to handle CursorUp at the top of the buffer when there are scroll (i.e. buffer.active.viewportY and buffer.active.baseY > 0), I tried to do:

xterm.scrollLines(-1)
xterm.write('\x1B[A') // cursorUp

But that doesn't work probably becuase buffer.active.Y is already 0.

Or maybe scrollLines() didn't update the buffer.active.viewportY/baseY (I saw that they remain unchanged after the scroll happens.

[Tyriar]

scrollLines should update synchronously:

xterm.js/src/common/services/BufferService.ts

Lines 128 to 150 in f6c4aee

	public scrollLines(disp: number, suppressScrollEvent?: boolean, source?: ScrollSource): void {
	const buffer = this.buffer;
	if (disp < 0) {
	if (buffer.ydisp === 0) {
	return;
	}
	this.isUserScrolling = true;
	} else if (disp + buffer.ydisp >= buffer.ybase) {
	this.isUserScrolling = false;
	}
	const oldYdisp = buffer.ydisp;
	buffer.ydisp = Math.max(Math.min(buffer.ydisp + disp, buffer.ybase), 0);
	// No change occurred, don't trigger scroll/refresh
	if (oldYdisp === buffer.ydisp) {
	return;
	}
	if (!suppressScrollEvent) {
	this._onScroll.fire(buffer.ydisp);
	}
	}

It will update viewportY, not baseY. It might be doing something different from what you want, it seems to work as expected for me?

[unional]

My case seems to be an edge case. When the buffer.active.y is 0.

i.e. at the top of the viewport.

I tried doing the same thing when y is not 0 and it is working correctly.