public void scrollViewportDown(boolean intoScrollBack) {
		if (scrollStart == scrollEnd) {
			return;
		}
		VtLine temp;
		if (intoScrollBack && scrollStart == 0 && maxScrollBack > 0) {
			temp = scrollBack.size() >= maxScrollBack ? scrollBack.remove() : null;
			scrollBack.add(lines.remove(0));
		}
		else {
			temp = lines.remove(scrollStart);
		}

		if (temp == null) {
			temp = new VtLine(cols);
		}
		else {
			temp.reset(cols);
		}
		lines.add(scrollEnd - 1, temp); // Account for removed line
	}
Scroll the viewport down a line

<p>
The lines are shifted upward. The line at the top of the viewport is removed, and a blank
line is inserted at the bottom of the viewport. If the viewport includes the display's top
line and intoScrollBack is specified, the line is shifted into the scroll-back buffer.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/terminal/vt/VtBuffer.java