[johncolanduoni]

A lot of these don’t happen on scroll and hover under normal circumstances. For example smooth scrolling on touchscreens is implemented by only re-running the compositor on each frame, and using the existing GPU-resident bitmap of the text being scrolled. That’s why non-passive onscroll callbacks make scrolling suck, especially on mobile.

[immibis]

What's not stated, is that we used to re-render the text at the bottom each time you scrolled up, and could still do it pretty fast (not quite in 16.67 milliseconds but we could have if computers had been today's speed), and in the meantime, we seem to have forgotten how to do that. Although we also have more pixels now, which probably changes things.

[toast0]

> we used to re-render the text at the bottom each time you scrolled up, and could still do it pretty fast

If you go back far enough, the IBM graphics cards used a text mode where text was accelerated by the graphics card, software would write a attribute byte and a data byte and the card had a bitmapped font to render text. VGA text mode at least could use hardware windowing so scrolling could also be accelerated; not every system used it, but you can set the start address and a line number where it returns to the start of the data area. That makes it easy to scroll without having to rewrite the screen buffer all at once. (If you set the stride to something that evenly divides the screen buffer and is at least as wide as your lines, it makes things even easier)