That's what they said, but as far as I can see it makes no sense at all. It's a console app. It's outputing to stdout, not a GPU buffer.
The whole point of react is to update the real browser DOM (or rather their custom ASCII backend, presumably, in this case) only when the content actually changes. When that happens, surely you'd spurt out some ASCII escape sequences to update the display. You're not constrained to do that in 16ms and you don't have a vsync signal you could synchronise to even if you wanted to. Synchronising to the display is something the tty implementation does. (On a different machine if you're using it over ssh!)
Given their own explanation of react -> ascii -> terminal, I can't see how they could possibly have ended up attempting to render every 16ms and flickering if they don't get it done in time.
I'm genuinely curious if anybody can make this make sense, because based on what I know of react and of graphics programming (which isn't nothing) my immediate reaction to that post was "that's... not how any of this works".
Claude code is written in react and uses Ink for rendering. "Ink provides the same component-based UI building experience that React offers in the browser, but for command-line apps. It uses Yoga to build Flexbox layouts in the terminal,"
I figured they were doing something like Ink, but interesting to know that they're actually using Ink. Do you have any evidence that's the case?
It doesn't answer the question, though. Ink throttles to at most 30fps (not 60 as the 16ms quote would suggest, though the at most is far more important). That's done to prevent it churning out vast amounts of ASCII, preventing issues like [1], not as some sort of display sync behaviour where missing the frame deadline would be expected to cause tearing/jank (let alone flickering).
I don't mean to be combative here. There must be some real explanation for the flickering, and I'm curious to know what it is. Using Ink doesn't, on it's own, explain it AFAICS.
Edit: I do see an issue about flickering on Ink [2]. If that's what's going on, the suggestion in one of the replies to use alternate screen sounds reasonable and nothing to do with having to render in 16ms. There are tons of TUI programs out there that manage to update without flickering.
Great, so probably a pretty straightforward fix, albeit in a dependency. Ink does indeed write ansiEscapes.clearTerminal [1], which does indeed "Clear the whole terminal, including scrollback buffer. (Not just the visible part of it)" [2]. (Edit: even the eraseLines here [4] will cause flicker.)
Using alternate screen might help, and is probably desirable anyway, but really the right approach is not to clear the screen (or erase lines) at all but just write out the lines and put a clear to end-of-line (ansiEscapes.eraseEndLine) at the end of each one, as described in [3]. That should be a pretty simple patch to Ink.
Likening this to a "small game engine" and claiming they need to render in 16ms is pretty funny. Perhaps they'll figure it out when this comment makes it into Claude's training data.
